HHH-4936 - Document JPA criteria queries
git-svn-id: https://svn.jboss.org/repos/hibernate/core/trunk@18867 1b8cb986-b30d-0410-93ca-fae66ebed9b2
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Steve Ebersole
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<!ENTITY versionNumber "WORKING">
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<!ENTITY today "TODAY">
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<!ENTITY copyrightYear "2004">
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<!ENTITY copyrightHolder "Red Hat Middleware, LLC.">
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<!ENTITY copyrightHolder "Red Hat, Inc.">
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<!ENTITY semi ";">
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@ -26,218 +26,532 @@
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<chapter id="querycriteria">
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<title>Criteria Queries</title>
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<note>
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<para>
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This chapter elaborates on the material discussed in
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<citetitle pubwork="chapter">Chapter 6 Criteria API</citetitle>
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of<citation>JPA 2 Specification</citation>.
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</para>
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</note>
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<para>
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Criteria queries are a programmatic, type-safe way to express a query. They are type-safe
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in terms of using interfaces and classes to represent various structural parts of a query
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such as the query itself, or the select clause, or an order-by, etc. They can also be
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type-safe in terms of referencing attributes as we will see in a bit. Users of the older
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Hibernate
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<interfacename>org.hibernate.Criteria</interfacename>
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query API will recognize
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Hibernate <interfacename>org.hibernate.Criteria</interfacename> query API will recognize
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the general approach, though we believe the JPA API to be superior as it represents a clean
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look at the lessons learned from that API. There are essentially 2 phases to performing
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a criteria query:
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<orderedlist>
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<listitem>
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<para>
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<link linkend="querycriteria-building">Building the criteria instance</link>
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</para>
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</listitem>
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<listitem>
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<para>
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<link linkend="querycriteria-executing">Executing the criteria instance</link>
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</para>
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</listitem>
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</orderedlist>
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look at the lessons learned from that API.
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</para>
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<para>
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Criteria queries are essentially an object graph, where each part of the graph represents an increasing
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(as we navigate down this graph) more atomic part of query. The first step in performing a criteria query
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is building this graph. The <interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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interface is the first thing with which you need to become acquainted to begin using criteria queries. Its
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role is that of a factory for all the individual pieces of the criteria. You obtain a
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<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename> instance by calling the
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<methodname>getCriteriaBuilder</methodname> method of the
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<interfacename>javax.persistence.EntityManagerFactory</interfacename>
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</para>
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<section id="querycriteria-building">
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<title>Criteria query building</title>
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<programlisting>CriteriaBuilder builder = entityManagerFactory.getCriteriaBuilder();</programlisting>
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<para>
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The next step is to obtain a <interfacename>javax.persistence.criteria.CriteriaQuery</interfacename>.
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You do this by one of the 3 methods on <interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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for this puropse.
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</para>
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<programlisting><![CDATA[CriteriaQuery<T> createQuery(Class<T>)]]></programlisting>
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<programlisting><![CDATA[CriteriaQuery<Tuple> createTupleQuery()]]></programlisting>
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<programlisting><![CDATA[CriteriaQuery<Object> createQuery()]]></programlisting>
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<para>
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Each serves a different purpose depending on the expected type of the query results.
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</para>
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<note>
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<para>
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Criteria queries are essentially an object graph, where each part of the graph
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represents an increasing (as we navigate down this graph) more atomic part of
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query. The first step in performing a criteria query is building this graph.
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<citetitle pubwork="chapter">Chapter 6 Criteria API</citetitle> of the
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<citation><xref linkend="JPA2"/></citation> already contains a decent amount of reference material
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pertaining to the various parts of a criteria query. So rather than duplicate all that content here,
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lets instead look at some of the more widely (anticipated) usages of the API.
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</para>
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<section id="querycriteria-builder">
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<title>CriteriaBuilder</title>
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</note>
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<section id="querycriteria-typedquery">
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<title>Typed criteria queries</title>
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<programlisting><![CDATA[CriteriaQuery<T> createQuery(Class<T>)]]></programlisting>
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<para>
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The type of the criteria query (aka the <T>) indicates the expected types in the
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query result. This might be an entity, an Integer, or any other object.
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</para>
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<section id="querycriteria-typedquery-entity">
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<title>Selecting an entity</title>
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<para>
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The
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<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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interface is the
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first thing with which you need to become acquainted to begin using criteria queries. Its role
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is a factory for all the individual pieces of the criteria. You obtain a
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<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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instance by calling
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the
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<methodname>javax.persistence.EntityManagerFactory.getCriteriaBuilder</methodname>
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method:
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This the most used form of query in Hibernate Query Language (HQL) and Hibernate Criteria Queries.
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You have an entity and you want to select one or more of that entity based on some condition.
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</para>
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<programlisting>CriteriaBuilder builder = entityManagerFactory.getCriteriaBuilder();</programlisting>
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<example id="ex-criteria-typedquery-entity">
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<title>Selecting the root entity</title>
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<programlistingco role="JAVA">
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<areaspec>
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<areaset id="ex.criteria.typedquery.entity.1" coords="">
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<area id="ex.criteria.typedquery.entity.1.c1" coords='1'/>
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<area id="ex.criteria.typedquery.entity.1.c2" coords='6'/>
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</areaset>
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<area id="ex.criteria.typedquery.entity.2" coords="3" />
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<area id="ex.criteria.typedquery.entity.3" coords="4" />
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</areaspec>
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<programlisting><![CDATA[CriteriaQuery<Person> criteria = builder.createQuery( Person.class );
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Root<Person> personRoot = criteria.from( Person.class );
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criteria.select( personRoot );
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criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
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List<Person> people = em.createQuery( criteria ).getResultList();
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for ( Person person : people ) { ... }]]></programlisting>
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</programlistingco>
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<calloutlist>
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<callout arearefs="ex.criteria.typedquery.entity.1">
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<para>
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We use the form <emphasis>createQuery( Person.class )</emphasis>
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here because the expected returns are in fact Person entities as we see when we
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begin processing the results.
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</para>
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</callout>
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<callout arearefs="ex.criteria.typedquery.entity.2">
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<para>
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<emphasis>personCriteria.select( personRoot )</emphasis> here is completely
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unneeded in this specific case because of the fact that <emphasis>personRoot</emphasis>
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will be the implied selection since we have only a single root. It was done here only
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for completeness of an example
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</para>
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</callout>
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<callout arearefs="ex.criteria.typedquery.entity.3">
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<para>
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<emphasis>Person_.eyeColor</emphasis> is an example of the static form of metamodel
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reference. We will use that form exclusively in this chapter.
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See (todo link to metamodel section once written).
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</para>
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</callout>
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</calloutlist>
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</example>
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</section>
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<section id="querycriteria-criteria">
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<title>CriteriaQuery creation</title>
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<section id="querycriteria-typedquery-expression">
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<title>Selecting a value</title>
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<para>
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Once you have the
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<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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reference
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you can begin building the pieces of the criteria query. First, you will need a
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<interfacename>javax.persistence.criteria.CriteriaQuery</interfacename>
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instance.
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<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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defines 3 methods
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for obtaining a
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<interfacename>javax.persistence.criteria.CriteriaQuery</interfacename>
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instance:
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The simplest form of selecting a value is selecting a particular attribute from an entity. But
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this might also be an aggregation, a mathematical operation, etc.
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</para>
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<itemizedlist>
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<listitem>
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<programlisting><![CDATA[CriteriaQuery<T> createQuery(Class<T>)]]></programlisting>
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</listitem>
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<listitem>
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<programlisting><![CDATA[CriteriaQuery<Tuple> createTupleQuery()]]></programlisting>
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</listitem>
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<listitem>
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<programlisting><![CDATA[CriteriaQuery<Object> createQuery()]]></programlisting>
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</listitem>
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</itemizedlist>
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<para>
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Each serves a different purpose depending on the expected type of the query results. The type
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is "carried forward" to the
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<interfacename>javax.persistence.TypedQuery</interfacename>
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we
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create from this
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<interfacename>javax.persistence.criteria.CriteriaQuery</interfacename>
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as
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we will see later in<xref linkend="querycriteria-executing"/>later.
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</para>
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<section id="querycriteria-criteria-typed">
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<title>Typed CriteriaQuery</title>
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<programlisting>
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<![CDATA[CriteriaQuery<Person> personCriteria = builder.createQuery(Person.class);]]></programlisting>
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<para>
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Basically this is saying to create a criteria where the results of this query will be of type
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Person. Person might be an entity or it might not. The type could even be simple types like
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<classname>java.lang.Integer</classname>,<classname>java.lang.String</classname>, etc. We
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will discuss this topic in more detail in
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<xref linkend="querycriteria-selection"/>
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</para>
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</section>
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<section id="querycriteria-criteria-tuple">
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<title>Tuple CriteriaQuery</title>
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<programlisting>
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<![CDATA[CriteriaQuery<Tuple> personCriteria = builder.createTupleQuery();]]></programlisting>
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<programlisting>
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<![CDATA[CriteriaQuery<Tuple> personCriteria = builder.createQuery(Tuple.class);]]></programlisting>
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<para>
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These two forms are exactly the same. Both say to create a criteria where the results of this
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query will be of type<interfacename>javax.persistence.Tuple</interfacename>. The term tuple is
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taken from mathematics, but its intent here is simply to mean a plurality; namely we are saying
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that each query result will actually be multiple values, a projection. The
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<interfacename>javax.persistence.Tuple</interfacename>
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instance gives us typed access to these
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multiple result values after the query has been executed. We will discuss accessing the query
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results via a
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<interfacename>javax.persistence.Tuple</interfacename>
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in
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<xref linkend="querycriteria-executing"/>.
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</para>
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</section>
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<section id="querycriteria-criteria-untyped">
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<title>Untyped CriteriaQuery</title>
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<programlisting>
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<![CDATA[CriteriaQuery<Object> personCriteria = builder.createQuery();]]></programlisting>
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<programlisting>
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<![CDATA[CriteriaQuery<Object> personCriteria = builder.createQuery(Object.class);]]></programlisting>
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<para>
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These two forms are exactly the same. Both say to create a criteria where the results of this
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query could be anything. Not generally recommended as you obviously lose the type safety.
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</para>
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</section>
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<example id="ex-criteria-typedquery-attribute">
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<title>Selecting an attribute</title>
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<programlistingco role="JAVA">
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<areaspec>
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<areaset id="ex.criteria.typedquery.attr.1" coords="">
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<area id="ex.criteria.typedquery.attr.1.c1" coords='1'/>
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<area id="ex.criteria.typedquery.attr.1.c2" coords='5'/>
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</areaset>
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<area id="ex.criteria.typedquery.attr.2" coords="3" />
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</areaspec>
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<programlisting><![CDATA[CriteriaQuery<Integer> criteria = builder.createQuery( Integer.class );
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Root<Person> personRoot = criteria.from( Person.class );
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criteria.select( personRoot.get( Person_.age ) );
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criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
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List<Integer> ages = em.createQuery( criteria ).getResultList();
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for ( Integer age : ages ) { ... } ]]></programlisting>
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</programlistingco>
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<calloutlist>
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<callout arearefs="ex.criteria.typedquery.attr.1">
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<para>
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Notice again the typing of the query based on the anticipated result type(s). Here
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we are specifying <classname>java.lang.Integer</classname> as the type of the
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<emphasis>Person#age</emphasis> attribute is <classname>java.lang.Integer</classname>.
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</para>
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</callout>
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<callout arearefs="ex.criteria.typedquery.attr.2">
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<para>
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We need to bind the fact that we are interested in the age associated with the
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<emphasis>personRoot</emphasis>. We might have multiple references to the Person
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entity in the query so we need to identify (aka qualify) which
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<emphasis>Person#age</emphasis> we mean.
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</para>
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</callout>
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</calloutlist>
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</example>
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<example id="ex-criteria-typedquery-expression">
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<title>Selecting an expression</title>
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<programlistingco role="JAVA">
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<areaspec>
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<area id="ex.criteria.typedquery.expr.1" coords="3" />
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</areaspec>
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<programlisting><![CDATA[CriteriaQuery<Integer> criteria = builder.createQuery( Integer.class );
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Root<Person> personRoot = criteria.from( Person.class );
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criteria.select( builder.max( personRoot.get( Person_.age ) ) );
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criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
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Integer maxAge = em.createQuery( criteria ).getSingleResult();]]></programlisting>
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</programlistingco>
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<calloutlist>
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<callout arearefs="ex.criteria.typedquery.expr.1">
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<para>
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Here we see <interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
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used to obtain a <emphasis>MAX</emphasis> expression. These expression building
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methods return <interfacename>javax.persistence.criteria.Expression</interfacename>
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instances typed according to various rules. The rule for a <emphasis>MAX</emphasis>
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expression is that the expression type is the same as that of the underlying attribute.
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</para>
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</callout>
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</calloutlist>
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</example>
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</section>
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<section id="querycriteria-from">
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<title>FROM clause</title>
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<blockquote>
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<attribution>
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<citation>
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<citation>JPA 2 Specification</citation>
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</citation>
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</attribution>
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<para>
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A CriteriaQuery object defines a query over one or more entity, embeddable, or basic abstract
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schema types. The root objects of the query are entities, from which the other types are reached
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by navigation.
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</para>
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</blockquote>
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<para>All the individual parts of the FROM clause (roots, joins, paths) implement the
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<interfacename>javax.persistence.criteria.From</interfacename>
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interface.
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<section id="querycriteria-typedquery-multiselect">
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<title>Selecting multiple values</title>
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<para>
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There are actually a few different ways to select multiple values using criteria queries. We will
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explore 2 options here, but an alternative recommended approach is to use tuples as
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described in <xref linkend="querycriteria-tuple"/>
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</para>
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<section id="querycriteria-from-root">
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<title>Roots</title>
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<para>Roots define the basis from which all joins, paths and attributes are available in the query. It
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is
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the root of the portion of your domain model you wish to query against. In a criteria query, a root
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is always an entity. Roots are defined and added to the criteria by the overloaded
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<methodname>from</methodname>
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methods on<interfacename>javax.persistence.criteria.CriteriaQuery</interfacename>:
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</para>
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<programlisting><![CDATA[<X> Root<X> from(Class<X>)]]></programlisting>
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<programlisting><![CDATA[<X> Root<X> from(EntityType<X>)]]></programlisting>
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<example id="ex-criteria-typedquery-array">
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<title>Selecting an array</title>
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<programlistingco role="JAVA">
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<areaspec>
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<areaset id="ex.criteria.typedquery.array.1" coords="">
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<area id="ex.criteria.typedquery.array.1.c1" coords='1'/>
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<area id="ex.criteria.typedquery.array.1.c2" coords='7'/>
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</areaset>
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<area id="ex.criteria.typedquery.array.2" coords="5" />
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</areaspec>
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<programlisting><![CDATA[CriteriaQuery<Object[]> criteria = builder.createQuery( Object[].class );
|
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Root<Person> personRoot = criteria.from( Person.class );
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Path<Long> idPath = personRoot.get( Person_.id );
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Path<Integer> agePath = personRoot.get( Person_.age );
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criteria.select( builder.array( idPath, agePath ) );
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criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
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List<Object[]> valueArray = em.createQuery( criteria ).getResultList();
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for ( Object[] values : valueArray ) {
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final Long id = (Long) values[0];
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final Integer age = (Integer) values[1];
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...
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}]]></programlisting>
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</programlistingco>
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<calloutlist>
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<callout arearefs="ex.criteria.typedquery.array.1">
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<para>
|
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Technically this is classified as a typed query, but as you can see in handling the
|
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results that is sort of misleading. Anyway, the expected result type here is an
|
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array.
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</para>
|
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</callout>
|
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<callout arearefs="ex.criteria.typedquery.array.2">
|
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<para>
|
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Here we see the use of the <methodname>array</methodname> method of the
|
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<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename> which
|
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explicitly combines individual selections into a
|
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<interfacename>javax.persistence.criteria.CompoundSelection</interfacename>.
|
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</para>
|
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</callout>
|
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</calloutlist>
|
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</example>
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<example id="ex-criteria-typedquery-array2">
|
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<title>Selecting an array (2)</title>
|
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<programlistingco role="JAVA">
|
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<areaspec>
|
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<areaset id="ex.criteria.typedquery.array2.1" coords="">
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<area id="ex.criteria.typedquery.array2.1.c1" coords='1'/>
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<area id="ex.criteria.typedquery.array2.1.c2" coords='7'/>
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</areaset>
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<area id="ex.criteria.typedquery.array2.2" coords="5" />
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</areaspec>
|
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<programlisting><![CDATA[CriteriaQuery<Object[]> criteria = builder.createQuery( Object[].class );
|
||||
Root<Person> personRoot = criteria.from( Person.class );
|
||||
Path<Long> idPath = personRoot.get( Person_.id );
|
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Path<Integer> agePath = personRoot.get( Person_.age );
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criteria.multiselect( idPath, agePath );
|
||||
criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
|
||||
List<Object[]> valueArray = em.createQuery( criteria ).getResultList();
|
||||
for ( Object[] values : valueArray ) {
|
||||
final Long id = (Long) values[0];
|
||||
final Integer age = (Integer) values[1];
|
||||
...
|
||||
} ]]></programlisting>
|
||||
</programlistingco>
|
||||
<calloutlist>
|
||||
<callout arearefs="ex.criteria.typedquery.array2.1">
|
||||
<para>
|
||||
Just as we saw in <xref linkend="ex-criteria-typedquery-array"/> we have
|
||||
a "typed" criteria query returning an Object array.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.typedquery.array2.2">
|
||||
<para>
|
||||
This actually functions exactly the same as what we saw in
|
||||
<xref linkend="ex-criteria-typedquery-array"/>. The <methodname>multiselect</methodname>
|
||||
method behaves slightly differently based on the type given when the criteria query
|
||||
was first built, but in this case it says to select and return an
|
||||
<emphasis>Object[]</emphasis>.
|
||||
</para>
|
||||
</callout>
|
||||
</calloutlist>
|
||||
</example>
|
||||
</section>
|
||||
|
||||
<section id="querycriteria-typedquery-construct">
|
||||
<title>Selecting a wrapper</title>
|
||||
<para>
|
||||
Another alternative to <xref linkend="querycriteria-typedquery-multiselect"/> is to instead select
|
||||
an object that will "wrap" the multiple values. Going back to the example query there, rather than
|
||||
returning an array of <emphasis>[Person#id, Person#age]</emphasis> instead declare a class
|
||||
that holds these values and instead return that.
|
||||
</para>
|
||||
<example id="ex-criteria-typedquery-construct">
|
||||
<title>Selecting an wrapper</title>
|
||||
<programlistingco role="JAVA">
|
||||
<areaspec>
|
||||
<areaset id="ex.criteria.typedquery.construct.1" coords="" >
|
||||
<area id="ex.criteria.typedquery.construct.1.c1" coords="1" />
|
||||
<area id="ex.criteria.typedquery.construct.1.c2" coords="4" />
|
||||
</areaset>
|
||||
<areaset id="ex.criteria.typedquery.construct.2" coords="">
|
||||
<area id="ex.criteria.typedquery.construct.2.c1" coords='11'/>
|
||||
<area id="ex.criteria.typedquery.construct.2.c2" coords='21'/>
|
||||
</areaset>
|
||||
<areaset id="ex.criteria.typedquery.construct.3" coords="" >
|
||||
<area id="ex.criteria.typedquery.construct.3.c1" coords="13" />
|
||||
<area id="ex.criteria.typedquery.construct.3.c2" coords="14" />
|
||||
</areaset>
|
||||
</areaspec>
|
||||
<programlisting><![CDATA[public class PersonWrapper {
|
||||
private final Long id;
|
||||
private final Integer age;
|
||||
public PersonWrapper(Long id, Integer age) {
|
||||
this.id = id;
|
||||
this.age = age;
|
||||
}
|
||||
...
|
||||
}
|
||||
...
|
||||
CriteriaQuery<PersonWrapper> criteria = builder.createQuery( PersonWrapper.class );
|
||||
Root<Person> personRoot = criteria.from( Person.class );
|
||||
criteria.select(
|
||||
builder.construct(
|
||||
PersonWrapper.class,
|
||||
personRoot.get( Person_.id ),
|
||||
personRoot.get( Person_.age )
|
||||
)
|
||||
);
|
||||
criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
|
||||
List<PersonWrapper> people = em.createQuery( criteria ).getResultList();
|
||||
for ( PersonWrapper person : people ) { ... }]]></programlisting>
|
||||
</programlistingco>
|
||||
<calloutlist>
|
||||
<callout arearefs="ex.criteria.typedquery.construct.1">
|
||||
<para>
|
||||
First we see the simple definition of the wrapper object we will be using to
|
||||
wrap our result values. Specifically notice the constructor and its argument types.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.typedquery.construct.2">
|
||||
<para>
|
||||
Since we will be returning <emphasis>PersonWrapper</emphasis> objects, we
|
||||
use <emphasis>PersonWrapper</emphasis> as the type of our criteria query.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.typedquery.construct.3">
|
||||
<para>
|
||||
Here we see another new <interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
|
||||
method, <methodname>construct</methodname>, which is used to builder a wrapper
|
||||
expression. Basically for every row in the result we are saying we would like
|
||||
a <emphasis>PersonWrapper</emphasis> instantiated by the matching constructor. This
|
||||
wrapper expression is then passed as the select.
|
||||
</para>
|
||||
</callout>
|
||||
</calloutlist>
|
||||
</example>
|
||||
</section>
|
||||
|
||||
</section>
|
||||
|
||||
<section id="querycriteria-tuple">
|
||||
<title>Tuple criteria queries</title>
|
||||
<para>
|
||||
A better approach to <xref linkend="querycriteria-typedquery-multiselect"/> is to either use
|
||||
a wrapper (which we just saw in <xref linkend="querycriteria-typedquery-construct"/>) or using
|
||||
the <interfacename>javax.persistence.Tuple</interfacename> contract.
|
||||
</para>
|
||||
|
||||
<example id="ex-criteria-typedquery-tuple">
|
||||
<title>Selecting a tuple</title>
|
||||
<programlistingco role="JAVA">
|
||||
<areaspec>
|
||||
<areaset id="ex.criteria.typedquery.tuple.1" coords="">
|
||||
<area id="ex.criteria.typedquery.tuple.1.c1" coords='1'/>
|
||||
<area id="ex.criteria.typedquery.tuple.1.c2" coords='7'/>
|
||||
</areaset>
|
||||
<area id="ex.criteria.typedquery.tuple.2" coords="5" />
|
||||
<areaset id="ex.criteria.typedquery.tuple.3" coords="">
|
||||
<area id="ex.criteria.typedquery.tuple.3.c1" coords='9'/>
|
||||
<area id="ex.criteria.typedquery.tuple.3.c2" coords='10'/>
|
||||
</areaset>
|
||||
</areaspec>
|
||||
<programlisting><![CDATA[CriteriaQuery<Tuple> criteria = builder.createTupleQuery();
|
||||
Root<Person> personRoot = criteria.from( Person.class );
|
||||
Path<Long> idPath = personRoot.get( Person_.id );
|
||||
Path<Integer> agePath = personRoot.get( Person_.age );
|
||||
criteria.multiselect( idPath, agePath );
|
||||
criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), "brown" ) );
|
||||
List<Tuple> tuples = em.createQuery( criteria ).getResultList();
|
||||
for ( Tuple tuple : valueArray ) {
|
||||
assert tuple.get( 0 ) == tuple.get( idPath );
|
||||
assert tuple.get( 1 ) == tuple.get( agePath );
|
||||
...
|
||||
} ]]></programlisting>
|
||||
</programlistingco>
|
||||
<calloutlist>
|
||||
<callout arearefs="ex.criteria.typedquery.tuple.1">
|
||||
<para>
|
||||
Here we see the use of a new <interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
|
||||
<interfacename>javax.persistence.criteria.CriteriaQuery</interfacename> building method,
|
||||
<methodname>createTupleQuery</methodname>. This is exactly equivalent to calling
|
||||
<emphasis>builder.createQuery( Tuple.class )</emphasis>. It signifies that we want
|
||||
to access the results through the <interfacename>javax.persistence.Tuple</interfacename> contract.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.typedquery.tuple.2">
|
||||
<para>
|
||||
Again we see the use of the <methodname>multiselect</methodname> method, just like
|
||||
in <xref linkend="ex-criteria-typedquery-array2"/>. The difference here is that the
|
||||
type of the <interfacename>javax.persistence.criteria.CriteriaQuery</interfacename> was defined
|
||||
as <interfacename>javax.persistence.Tuple</interfacename> so the compound selections in
|
||||
this case are interpreted to be the tuple elements.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.typedquery.tuple.3">
|
||||
<para>
|
||||
Here we see <interfacename>javax.persistence.Tuple</interfacename> allowing different types of
|
||||
access to the results, which we will expand on next.
|
||||
</para>
|
||||
</callout>
|
||||
</calloutlist>
|
||||
</example>
|
||||
|
||||
<section id="querycriteria-tuple-access">
|
||||
<title>Accessing tuple elements</title>
|
||||
<para>
|
||||
The <interfacename>javax.persistence.Tuple</interfacename> contract provides 3 basic forms of
|
||||
access to the underlying elements:
|
||||
</para>
|
||||
<variablelist>
|
||||
<varlistentry>
|
||||
<term>typed</term>
|
||||
<listitem>
|
||||
<programlisting><![CDATA[<X> X get(TupleElement<X> tupleElement)]]></programlisting>
|
||||
<para>
|
||||
This allows typed access to the underlying tuple elements. We see this in
|
||||
<xref linkend="ex-criteria-typedquery-tuple"/> in the <emphasis>tuple.get( idPath )</emphasis>
|
||||
and <emphasis>tuple.get( agePath )</emphasis> calls. Just about everything is a
|
||||
<interfacename>javax.persistence.TupleElement</interfacename>.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
<varlistentry>
|
||||
<term>positional</term>
|
||||
<listitem>
|
||||
<programlisting><![CDATA[Object get(int i)]]></programlisting>
|
||||
<programlisting><![CDATA[<X> X get(int i, Class<X> type)]]></programlisting>
|
||||
<para>
|
||||
Very similar to what we saw in <xref linkend="ex-criteria-typedquery-array"/> and
|
||||
<xref linkend="ex-criteria-typedquery-array2"/> in terms of positional access. Only the
|
||||
second form here provides typing, because the user explicitly provides the typing
|
||||
on access. We see this in <xref linkend="ex-criteria-typedquery-tuple"/> in
|
||||
the <emphasis>tuple.get( 0 )</emphasis> and <emphasis>tuple.get( 1 )</emphasis> calls.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
<varlistentry>
|
||||
<term>aliased</term>
|
||||
<listitem>
|
||||
<programlisting><![CDATA[Object get(String alias)]]></programlisting>
|
||||
<programlisting><![CDATA[<X> X get(String alias, Class<X> type)]]></programlisting>
|
||||
<para>
|
||||
Again, only the second form here provides typing, because the user explicitly provides
|
||||
the typing on access. We have not seen an example of using this, but its trivial. We
|
||||
would simply, for example, have applies an alias to either of the paths like
|
||||
<emphasis>idPath.alias( "id" )</emphasis> and/or <emphasis>agePath.alias( "age" )</emphasis>
|
||||
and we could have accessed the individual tuple elements by those specified aliases.
|
||||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
</variablelist>
|
||||
</section>
|
||||
|
||||
</section>
|
||||
|
||||
|
||||
|
||||
<section id="querycriteria-from">
|
||||
<title>FROM clause</title>
|
||||
<blockquote>
|
||||
<attribution>
|
||||
<citation><xref linkend="JPA2"/></citation>
|
||||
</attribution>
|
||||
<para>
|
||||
A CriteriaQuery object defines a query over one or more entity, embeddable, or basic abstract
|
||||
schema types. The root objects of the query are entities, from which the other types are reached
|
||||
by navigation.
|
||||
</para>
|
||||
</blockquote>
|
||||
|
||||
<note>
|
||||
<para>
|
||||
All the individual parts of the FROM clause (roots, joins, paths) implement the
|
||||
<interfacename>javax.persistence.criteria.From</interfacename> interface.
|
||||
</para>
|
||||
</note>
|
||||
|
||||
<section id="querycriteria-from-root">
|
||||
<title>Roots</title>
|
||||
<para>
|
||||
Roots define the basis from which all joins, paths and attributes are available in the query. In
|
||||
a criteria query, a root is always an entity. Roots are defined and added to the criteria by
|
||||
the overloaded <methodname>from</methodname> methods on
|
||||
<interfacename>javax.persistence.criteria.CriteriaQuery</interfacename>:
|
||||
</para>
|
||||
<programlisting><![CDATA[<X> Root<X> from(Class<X>)]]></programlisting>
|
||||
<programlisting><![CDATA[<X> Root<X> from(EntityType<X>)]]></programlisting>
|
||||
<example>
|
||||
<title>Adding a root</title>
|
||||
<programlisting><![CDATA[CriteriaQuery<Person> personCriteria = builder.createQuery( Person.class );
|
||||
// create and add the root
|
||||
person.from( Person.class );
|
||||
...]]></programlisting>
|
||||
<para>Criteria queries may define multiple roots, the effect of which is to create a cartesean product
|
||||
between the newly added root and the others. Here is an example matching all single men and all
|
||||
single women:
|
||||
</para>
|
||||
<programlisting><![CDATA[CriteriaQuery query = builder.createQuery();
|
||||
</example>
|
||||
|
||||
<para>
|
||||
Criteria queries may define multiple roots, the effect of which is to create a
|
||||
<ulink url="http://en.wikipedia.org/wiki/Cartesian_product">cartesian product</ulink>
|
||||
between the newly added root and the others. Here is an example matching all single men and all
|
||||
single women:
|
||||
</para>
|
||||
<programlisting><![CDATA[CriteriaQuery query = builder.createQuery();
|
||||
Root<Person> men = query.from( Person.class );
|
||||
Root<Person> women = query.from( Person.class );
|
||||
Predicate menRestriction = builder.and(
|
||||
builder.equal(
|
||||
men.get( Person_.gender ),
|
||||
Gender.MALE
|
||||
),
|
||||
builder.equal(
|
||||
men.get( Person_.relationshipStatus ),
|
||||
RelationshipStatus.SINGLE
|
||||
)
|
||||
builder.equal( men.get( Person_.gender ), Gender.MALE ),
|
||||
builder.equal( men.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE )
|
||||
);
|
||||
Predicate womenRestriction = builder.and(
|
||||
builder.equal(
|
||||
women.get( Person_.gender ),
|
||||
Gender.FEMALE
|
||||
),
|
||||
builder.equal(
|
||||
women.get( Person_.relationshipStatus ),
|
||||
RelationshipStatus.SINGLE
|
||||
)
|
||||
builder.equal( women.get( Person_.gender ), Gender.FEMALE ),
|
||||
builder.equal( women.get( Person_.relationshipStatus ), RelationshipStatus.SINGLE )
|
||||
);
|
||||
query.where(
|
||||
builder.and( menRestriction, womenRestriction )
|
||||
);]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-from-join">
|
||||
<title>Joins</title>
|
||||
<para>Joins allow navigation from other
|
||||
<interfacename>javax.persistence.criteria.From</interfacename>
|
||||
to either association or embedded attributes. Joins are created by the numerous overloaded
|
||||
<methodname>join</methodname>
|
||||
methods of the
|
||||
<interfacename>javax.persistence.criteria.From</interfacename>
|
||||
interface:
|
||||
</para>
|
||||
query.where( builder.and( menRestriction, womenRestriction ) );]]></programlisting>
|
||||
</section>
|
||||
|
||||
<section id="querycriteria-from-join">
|
||||
<title>Joins</title>
|
||||
<para>Joins allow navigation from other
|
||||
<interfacename>javax.persistence.criteria.From</interfacename>
|
||||
to either association or embedded attributes. Joins are created by the numerous overloaded
|
||||
<methodname>join</methodname>
|
||||
methods of the
|
||||
<interfacename>javax.persistence.criteria.From</interfacename>
|
||||
interface:
|
||||
</para>
|
||||
<example id="criteria-join-singular">
|
||||
<title>Example with Embedded and ManyToOne</title>
|
||||
<programlisting><![CDATA[CriteriaQuery<Person> personCriteria = builder.createQuery( Person.class );
|
||||
Root<Person> personRoot = person.from( Person.class );
|
||||
// Person.address is an embedded attribute
|
||||
|
|
@ -245,128 +559,105 @@ Join<Person,Address> personAddress = personRoot.join( Person_.address );
|
|||
// Address.country is a ManyToOne
|
||||
Join<Address,Country> addressCountry = personAddress.join( Address_.country );
|
||||
...]]></programlisting>
|
||||
<para>An example with collection attributes:</para>
|
||||
</example>
|
||||
<example id="criteria-join-plural">
|
||||
<title>Example with Collections</title>
|
||||
<programlisting><![CDATA[CriteriaQuery<Person> personCriteria = builder.createQuery( Person.class );
|
||||
Root<Person> personRoot = person.from( Person.class );
|
||||
Join<Person,Order> orders = personRoot.join( Person_.orders );
|
||||
Join<Order,LineItem> orderLines = orders.join( Order_.lineItems );
|
||||
...]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-from-fetch">
|
||||
<title>Fetches</title>
|
||||
<para>todo</para>
|
||||
</section>
|
||||
</example>
|
||||
</section>
|
||||
|
||||
<section id="querycriteria-from-fetch">
|
||||
<title>Fetches</title>
|
||||
<para>
|
||||
Just like in HQL and EJB-QL, we can specify that associated data be fetched along with the owner.
|
||||
Fetches are created by the numerous overloaded <methodname>fetch</methodname>
|
||||
methods of the <interfacename>javax.persistence.criteria.From</interfacename>
|
||||
interface:
|
||||
</para>
|
||||
<example id="criteria-fetch-singular">
|
||||
<title>Example with Embedded and ManyToOne</title>
|
||||
<programlisting><![CDATA[CriteriaQuery<Person> personCriteria = builder.createQuery( Person.class );
|
||||
Root<Person> personRoot = person.from( Person.class );
|
||||
// Person.address is an embedded attribute
|
||||
Join<Person,Address> personAddress = personRoot.fetch( Person_.address );
|
||||
// Address.country is a ManyToOne
|
||||
Join<Address,Country> addressCountry = personAddress.fetch( Address_.country );
|
||||
...]]></programlisting>
|
||||
</example>
|
||||
<note>
|
||||
<para>
|
||||
Technically speaking, embedded attributes are always fetched with their owner. However
|
||||
in order to define the fetching of <emphasis>Address#country</emphasis> we needed
|
||||
a <interfacename>javax.persistence.criteria.Fetch</interfacename> for its parent path.
|
||||
</para>
|
||||
</note>
|
||||
<example id="criteria-fetch-plural">
|
||||
<title>Example with Collections</title>
|
||||
<programlisting><![CDATA[CriteriaQuery<Person> personCriteria = builder.createQuery( Person.class );
|
||||
Root<Person> personRoot = person.from( Person.class );
|
||||
Join<Person,Order> orders = personRoot.fetch( Person_.orders );
|
||||
Join<Order,LineItem> orderLines = orders.fetch( Order_.lineItems );
|
||||
...]]></programlisting>
|
||||
</example>
|
||||
</section>
|
||||
|
||||
</section>
|
||||
|
||||
<section id="querycriteria-path">
|
||||
<title>Path expressions</title>
|
||||
<note>
|
||||
<para>
|
||||
Roots, joins and fetches are themselves paths as well
|
||||
Roots, joins and fetches are themselves paths as well.
|
||||
</para>
|
||||
</note>
|
||||
<para>todo</para>
|
||||
</section>
|
||||
<section id="querycriteria-selection">
|
||||
<title>Selections</title>
|
||||
<para>todo</para>
|
||||
</section>
|
||||
</section>
|
||||
<section id="querycriteria-executing">
|
||||
<title>Criteria query execution</title>
|
||||
<para>todo</para>
|
||||
</section>
|
||||
<section id="querycriteria-common">
|
||||
<title>Common use cases</title>
|
||||
<section id="querycriteria-common-selectroot">
|
||||
<title>Selecting the root entity</title>
|
||||
<programlisting><![CDATA[// get all people with brown eyes
|
||||
CriteriaQuery<Person> personCriteria = build.createQuery( Person.class );
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
// specifying select here is not strictly needed because 'personRoot'
|
||||
// will be the implied selection since we have only a single root;
|
||||
// but done here for explicitness
|
||||
personCriteria.select( personRoot );
|
||||
personCriteria.where( builder.equal( Person_.eyeColor, "brown" ) );
|
||||
List<Person> people = em.createQuery( personCriteria ).getResultList();]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-common-selectassociation">
|
||||
<title>Selecting an association</title>
|
||||
<programlisting><![CDATA[// get the gender of all people with brown eyes
|
||||
CriteriaQuery<Gender> personCriteria = build.createQuery( Gender.class );
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
// specifying select here is not strictly needed because 'personRoot'
|
||||
// will be the implied selection since we have only a single root;
|
||||
// but done here for explicitness
|
||||
personCriteria.select( personRoot );
|
||||
personCriteria.where( builder.equal( Person_.eyeColor, "brown" ) );
|
||||
List<Person> people = em.createQuery( personCriteria ).getResultList();]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-common-selectvalue">
|
||||
<title>Selecting a value</title>
|
||||
<programlisting><![CDATA[// get the height of all people with brown eyes
|
||||
CriteriaQuery<Integer> personCriteria = build.createQuery( Integer.class );
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
personCriteria.select( personRoot.get( Person.height ) );
|
||||
personCriteria.where( builder.equal( Person_.eyeColor, "brown" ) );
|
||||
List<Integer> heights = em.createQuery( personCriteria ).getResultList();]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-common-selectaggregation">
|
||||
<title>Selecting an aggregated value</title>
|
||||
<programlisting><![CDATA[// get the maximum height of all people with brown eyes
|
||||
CriteriaQuery<Integer> personCriteria = build.createQuery( Integer.class );
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
personCriteria.select( builder.max( personRoot.get( Person.height ) ) );
|
||||
personCriteria.where( builder.equal( Person_.eyeColor, "brown" ) );
|
||||
Integer maxHeight = em.createQuery( personCriteria ).getSingleResult();]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-common-selecttuple">
|
||||
<title>Selecting a tuple</title>
|
||||
<programlisting><![CDATA[// get the id, height and gender of all people with brown eyes
|
||||
CriteriaQuery<Tuple> personCriteria = build.createTupleQuery();
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
Path<Long> idPath = personRoot.get( Person_.id );
|
||||
idPath.setAlias( "id" );
|
||||
Path<Integer> heightPath = personRoot.get( Person_.height );
|
||||
Path<Gender> genderPath = personRoot.get( Person_.gender );
|
||||
personCriteria.multiselect( idPath, heightPath, genderPath );
|
||||
personCriteria.where( builder.equal( Person_.eyeColor, "brown" ) );
|
||||
List<Tuple> tuples = em.createQuery( personCriteria ).getResultList();
|
||||
for ( Tuple tuple : tuples ) {
|
||||
// the id value, for example, can be accessed by expression...
|
||||
handleId( tuple.get( idPath ) );
|
||||
// or by position...
|
||||
handleId( tuple.get( 0 ) );
|
||||
// or by the explicit alias we gave it...
|
||||
handleId( tuple.get( "id" ) );
|
||||
}]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-common-selectconstruct">
|
||||
<title>Selecting a constructed value</title>
|
||||
<programlisting><![CDATA[// get the id, height and gender of all people with brown eyes
|
||||
// like we did before, but this time wrap them in a "holder"
|
||||
CriteriaQuery<PersonHolder> personCriteria = build.createQuery( PersonHolder.class );
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
personCriteria.select(
|
||||
builder.construct(
|
||||
PersonHolder.class,
|
||||
personRoot.get( Person_.id ),
|
||||
personRoot.get( Person_.height ),
|
||||
personRoot.get( Person_.gender )
|
||||
)
|
||||
);
|
||||
List<PersonHolder> people = em.createQuery( personCriteria ).getResultList();]]></programlisting>
|
||||
</section>
|
||||
<section id="querycriteria-common-param">
|
||||
|
||||
|
||||
<section id="querycriteria-param">
|
||||
<title>Using parameters</title>
|
||||
<example id="ex-querycriteria-param" >
|
||||
<title>Using parameters</title>
|
||||
<programlisting><![CDATA[// get all people with brown eyes
|
||||
CriteriaQuery<Person> personCriteria = build.createQuery( Person.class );
|
||||
Root<Person> personRoot = personCriteria.from( Person.class );
|
||||
personCriteria.select( personRoot );
|
||||
<programlistingco>
|
||||
<areaspec>
|
||||
<area coords="4" id="ex.criteria.param.1"/>
|
||||
<area coords="5" id="ex.criteria.param.2"/>
|
||||
<area coords="7" id="ex.criteria.param.3"/>
|
||||
</areaspec>
|
||||
<programlisting><![CDATA[CriteriaQuery<Person> criteria = build.createQuery( Person.class );
|
||||
Root<Person> personRoot = criteria.from( Person.class );
|
||||
criteria.select( personRoot );
|
||||
ParameterExpression<String> eyeColorParam = builder.parameter( String.class );
|
||||
personCriteria.where( builder.equal( Person_.eyeColor, eyeColorParam ) );
|
||||
TypedQuery<Person> query = em.createQuery( personCriteria );
|
||||
criteria.where( builder.equal( personRoot.get( Person_.eyeColor ), eyeColorParam ) );
|
||||
TypedQuery<Person> query = em.createQuery( criteria );
|
||||
query.setParameter( eyeColorParam, "brown" );
|
||||
List<Person> people = query.getResultList();]]></programlisting>
|
||||
</section>
|
||||
<calloutlist>
|
||||
<callout arearefs="ex.criteria.param.1">
|
||||
<para>
|
||||
Use the <methodname>parameter</methodname> method of
|
||||
<interfacename>javax.persistence.criteria.CriteriaBuilder</interfacename>
|
||||
to obtain a parameter reference.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.param.2">
|
||||
<para>
|
||||
Use the parameter reference in the criteria query.
|
||||
</para>
|
||||
</callout>
|
||||
<callout arearefs="ex.criteria.param.3">
|
||||
<para>
|
||||
Use the parameter reference to bind the parameter value to the
|
||||
<interfacename>javax.persistence.TypedQuery</interfacename>
|
||||
</para>
|
||||
</callout>
|
||||
</calloutlist>
|
||||
</programlistingco>
|
||||
|
||||
</example>
|
||||
</section>
|
||||
|
||||
</chapter>
|
||||
|
|
|
|||
Loading…
Reference in New Issue