hibernate-orm/reference/en/modules/query_sql.xml

<chapter id="querysql" revision="2">
    <title>Native SQL</title>

    <para>
        You may also express queries in the native SQL dialect of your database. This is useful if you
        want to utilize database specific features such as query hints or the <literal>CONNECT</literal> 
        keyword in Oracle. It also provides a clean migration path from a direct SQL/JDBC based 
        application to Hibernate.
    </para>

    <para>
        Hibernate3 allows you to specify handwritten SQL (including stored procedures) for 
        all create, update, delete, and load operations. 
    </para>

    <sect1 id="querysql-creating" revision="2">
        <title>Using a <literal>SQLQuery</literal></title>

        <para>
            Execution of native SQL queries is controlled via the <literal>SQLQuery</literal> interface, 
            which is obtained by calling <literal>Session.createSQLQuery()</literal>. In extremely
            simple cases, we can use the following form:
        </para>

        <programlisting><![CDATA[List cats = sess.createSQLQuery("select * from cats")
    .addEntity(Cat.class)
    .list();]]></programlisting>
    
        <para>
            This query specified:
        </para>

        <itemizedlist>
        <listitem>
        <para>
            the SQL query string
        </para>
        </listitem>
        <listitem>
        <para>
            the entity returned by the query
        </para>
        </listitem>
        </itemizedlist>

        <para>
            Here, the result set column names are assumed to be the same as the column names
            specified in the mapping document. This can be problematic for SQL queries which
            join multiple tables, since the same column names may appear in more than one
            table. The following form is not vulnerable to column name duplication:
        </para>

        <programlisting><![CDATA[List cats = sess.createSQLQuery("select {cat.*} from cats cat")
    .addEntity("cat", Cat.class)
    .list();]]></programlisting>

        <para>
            This query specified:
        </para>

        <itemizedlist>
        <listitem>
        <para>
            the SQL query string, with a placeholder for Hibernate to inject the column aliases
        </para>
        </listitem>
        <listitem>
        <para>
            the entity returned by the query, and its SQL table alias
        </para>
        </listitem>
        </itemizedlist>
    
        <para>
            The <literal>addEntity()</literal> method associates the SQL table alias with the returned 
            entity class, and determines the shape of the query result set.
        </para>
        
        <para>
            The <literal>addJoin()</literal> method may be used to load associations to other entities
            and collections.
        </para>
        
        <programlisting><![CDATA[List cats = sess.createSQLQuery(
        "select {cat.*}, {kitten.*} from cats cat, cats kitten where kitten.mother = cat.id"
    )
    .addEntity("cat", Cat.class)
    .addJoin("kitten", "cat.kittens")
    .list();]]></programlisting>
    
        <para>
            A native SQL query might return a simple scalar value or a combination of scalars and
            entities.
        </para>

        <programlisting><![CDATA[Double max = (Double) sess.createSQLQuery("select max(cat.weight) as maxWeight from cats cat")
        .addScalar("maxWeight", Hibernate.DOUBLE);
        .uniqueResult();]]></programlisting>


    </sect1>

    <sect1 id="querysql-aliasreferences">
        <title>Alias and property references</title>

        <para>
            The <literal>{cat.*}</literal> notation used above is a shorthand for "all properties". 
            Alternatively, you may list the columns explicity, but even this case we let Hibernate 
            inject the SQL column aliases for each property. The placeholder for a column alias is 
            just the property name qualified by the table alias. In the following example, we retrieve 
            <literal>Cat</literal>s from a different table (<literal>cat_log</literal>) to the one 
            declared in the mapping metadata. Notice that we may even use the property aliases in the 
            where clause if we like.
        </para>
        <para>
            The <literal>{}</literal>-syntax is <emphasis>not</emphasis> required for named queries. 
            See <xref linkend="querysql-namedqueries"/>
        </para>

        <programlisting><![CDATA[String sql = "select cat.originalId as {cat.id}, " +
    "cat.mateid as {cat.mate}, cat.sex as {cat.sex}, " +
    "cat.weight*10 as {cat.weight}, cat.name as {cat.name} " +
    "from cat_log cat where {cat.mate} = :catId"
    
List loggedCats = sess.createSQLQuery(sql)
    .addEntity("cat", Cat.class)
    .setLong("catId", catId)
    .list();]]></programlisting>

        <para>
            <emphasis>Note:</emphasis> if you list each property explicitly, you must include all
            properties of the class <emphasis>and its subclasses</emphasis>!
        </para>

    </sect1>
    
    <sect1 id="querysql-namedqueries" revision="2">
        <title>Named SQL queries</title>

        <para>
            Named SQL queries may be defined in the mapping document and called in exactly the 
            same way as a named HQL query. In this case, we do <emphasis>not</emphasis> need 
            to call <literal>addEntity()</literal>.
        </para>

         <programlisting><![CDATA[<sql-query name="persons">
    <return alias="person" class="eg.Person"/>
    SELECT person.NAME AS {person.name},
           person.AGE AS {person.age},
           person.SEX AS {person.sex}
    FROM PERSON person 
    WHERE person.NAME LIKE :namePattern
</sql-query>]]></programlisting>

        <programlisting><![CDATA[List people = sess.getNamedQuery("persons")
    .setString("namePattern", namePattern)
    .setMaxResults(50)
    .list();]]></programlisting>

         <para>
             The <literal>&lt;return-join&gt;</literal> and <literal>&lt;load-collection&gt;</literal>
             elements are used to join associations and define queries which initialize collections,
             respectively.
         </para>
         
         <programlisting><![CDATA[<sql-query name="personsWith">
    <return alias="person" class="eg.Person"/>
    <return-join alias="address" property="person.mailingAddress"/>
    SELECT person.NAME AS {person.name},
           person.AGE AS {person.age},
           person.SEX AS {person.sex},
           adddress.STREET AS {address.street},
           adddress.CITY AS {address.city},
           adddress.STATE AS {address.state},
           adddress.ZIP AS {address.zip}
    FROM PERSON person 
    JOIN ADDRESS adddress
    	ON person.ID = address.PERSON_ID AND address.TYPE='MAILING'
    WHERE person.NAME LIKE :namePattern
</sql-query>]]></programlisting>

        <para>
            A named SQL query may return a scalar value. You must specfy the column alias
            and Hibernate type using the <literal>&lt;return-scalar&gt;</literal> element:
        </para>
        
        <programlisting><![CDATA[<sql-query name="mySqlQuery">
    <return-scalar column="name" type="string"/>
    <return-scalar column="age" type="long"/>
    SELECT p.NAME AS name,
           p.AGE AS age,
    FROM PERSON p WHERE p.NAME LIKE 'Hiber%'
</sql-query>]]></programlisting>

         <sect2 id="propertyresults">
             <title>Using return-property to explicitly specify column/alias names</title>
             
             <para>
                 With <literal>&lt;return-property&gt;</literal> you can explicitly tell Hibernate what column
                 aliases to use, instead of using the <literal>{}</literal>-syntax to let Hibernate inject its 
                 own aliases.                 
             </para>
             
            <programlisting><![CDATA[<sql-query name="mySqlQuery">
    <return alias="person" class="eg.Person">
        <return-property name="name" column="myName"/>
        <return-property name="age" column="myAge"/>
        <return-property name="sex" column="mySex"/>
    </return>
    SELECT person.NAME AS myName,
           person.AGE AS myAge,
           person.SEX AS mySex,
    FROM PERSON person WHERE person.NAME LIKE :name
</sql-query>
]]></programlisting>
             
             <para>
                 <literal>&lt;return-property&gt;</literal> also works with multiple columns. This solves a 
                 limitation with the <literal>{}</literal>-syntax which can not allow fine grained control 
                 of multi-column properties.
             </para>
             
             <programlisting><![CDATA[<sql-query name="organizationCurrentEmployments">
    <return alias="emp" class="Employment">            
        <return-property name="salary"> 
            <return-column name="VALUE"/>
            <return-column name="CURRENCY"/>            
        </return-property>
        <return-property name="endDate" column="myEndDate"/>
    </return>
        SELECT EMPLOYEE AS {emp.employee}, EMPLOYER AS {emp.employer}, 
        STARTDATE AS {emp.startDate}, ENDDATE AS {emp.endDate},
        REGIONCODE as {emp.regionCode}, EID AS {emp.id}, VALUE, CURRENCY
        FROM EMPLOYMENT
        WHERE EMPLOYER = :id AND ENDDATE IS NULL
        ORDER BY STARTDATE ASC
</sql-query>]]></programlisting>
             
            <para>
                Notice that in this example we used <literal>&lt;return-property&gt;</literal> in combination
                with the <literal>{}</literal>-syntax for injection. Allowing users to choose 
                how they want to refer column and properties.
            </para>

            <para>
                If your mapping has a discriminator you must use <literal>&lt;return-discriminator&gt;</literal> 
                to specify the discriminator column.
            </para>
         </sect2>
         
         <sect2 id="sp_query">
             <title>Using stored procedures for querying</title>
             
             <para>
                 Hibernate 3 introduces support for queries via stored procedures. The stored procedures must 
                 return a resultset as the first out-parameter to be able to work with Hibernate. An example 
                 of such a stored procedure in Oracle 9 and higher is as follows:
             </para>
                 
                 <programlisting><![CDATA[CREATE OR REPLACE FUNCTION selectAllEmployments 
    RETURN SYS_REFCURSOR 
AS 
    st_cursor SYS_REFCURSOR; 
BEGIN 
    OPEN st_cursor FOR 
 SELECT EMPLOYEE, EMPLOYER, 
 STARTDATE, ENDDATE, 
 REGIONCODE, EID, VALUE, CURRENCY 
 FROM EMPLOYMENT; 
      RETURN  st_cursor; 
 END;]]></programlisting>
                 
             <para>
                 To use this query in Hibernate you need to map it via a named query.
             </para>
                 
             <programlisting><![CDATA[<sql-query name="selectAllEmployees_SP" callable="true">
    <return alias="emp" class="Employment">
        <return-property name="employee" column="EMPLOYEE"/>
        <return-property name="employer" column="EMPLOYER"/>            
        <return-property name="startDate" column="STARTDATE"/>
        <return-property name="endDate" column="ENDDATE"/>            
        <return-property name="regionCode" column="REGIONCODE"/>            
        <return-property name="id" column="EID"/>                        
        <return-property name="salary"> 
            <return-column name="VALUE"/>
            <return-column name="CURRENCY"/>            
        </return-property>
    </return>
    { ? = call selectAllEmployments() }
</sql-query>]]></programlisting>
             
             <para>
               Notice stored procedures currently only return scalars and entities. 
               <literal>&lt;return-join&gt;</literal> and <literal>&lt;load-collection&gt;</literal> 
               are not supported.
             </para>
             
             <sect3 id="querysql-limits-storedprocedures">
               <title>Rules/limitations for using stored procedures</title>
               
               <para>
                   To use stored procedures with Hibernate the procedures have to follow some rules. 
                   If they do not follow those rules they are not usable with Hibernate. If you still 
                   want to use these procedures you have to execute them via <literal>session.connection()</literal>.
                   The rules are different for each database, since database vendors have different stored
                   procedure semantics/syntax.
               </para>

               <para>
                   Stored procedure queries can't be paged with <literal>setFirstResult()/setMaxResults()</literal>.
               </para>

                 <para>
                   For Oracle the following rules apply:
               </para>
               
               <itemizedlist spacing="compact">
               <listitem>
               <para>    
                   The procedure must return a result set. This is done by returning a 
                   <literal>SYS_REFCURSOR</literal> in Oracle 9 or 10. In Oracle you 
                   need to define a <literal>REF CURSOR</literal> type.
               </para>
               </listitem>    
               <listitem>
               <para>    
                   Recommended form is <literal>{ ? = call procName(&lt;parameters&gt;) }</literal> 
                   or <literal>{ ? = call procName }</literal> (this is more an Oracle rule than a 
                   Hibernate rule).
               </para>
               </listitem>    
              </itemizedlist>
                           
              <para>                   
                   For Sybase or MS SQL server the following rules apply:
               </para>
                   
               <itemizedlist spacing="compact">
               <listitem>
               <para>    
                   The procedure must return a result set. Note that since these servers can/will return multiple
                   result sets and update counts, Hibernate will iterate the results and take the first result that
                   is a result set as its return value. Everything else will be discarded.
               </para>
               </listitem>    
               <listitem>
               <para>    
                   If you can enable <literal>SET NOCOUNT ON</literal> in your procedure it will probably be
                   more efficient, but this is not a requirement.
               </para>
               </listitem>    
              </itemizedlist>
              </sect3>
         </sect2>

    </sect1>

    <sect1 id="querysql-cud">
        <title>Custom SQL for create, update and delete</title>

        <para>
            Hibernate3 can use custom SQL statements for create, update, and delete operations.
            The class and collection persisters in Hibernate already contain a set of configuration
            time generated strings (insertsql, deletesql, updatesql etc.). The mapping tags
            <literal>&lt;sql-insert&gt;</literal>, <literal>&lt;sql-delete&gt;</literal>, and
            <literal>&lt;sql-update&gt;</literal> override these strings:
        </para>

        <programlisting><![CDATA[<class name="Person">
    <id name="id">
        <generator class="increment"/>
    </id>
    <property name="name" not-null="true"/>
    <sql-insert>INSERT INTO PERSON (NAME, ID) VALUES ( UPPER(?), ? )</sql-insert>
    <sql-update>UPDATE PERSON SET NAME=UPPER(?) WHERE ID=?</sql-update>
    <sql-delete>DELETE FROM PERSON WHERE ID=?</sql-delete>
</class>]]></programlisting>

        <para>
            The SQL is directly executed in your database, so you are free to use any dialect
            you like. This will of course reduce the portability of your mapping if you use database
            specific SQL.
        </para>

        <para>
            Stored procedures are supported if the <literal>callable</literal> attribute is set:
        </para>

    <programlisting><![CDATA[<class name="Person">
    <id name="id">
        <generator class="increment"/>
    </id>
    <property name="name" not-null="true"/>
    <sql-insert callable="true">{call createPerson (?, ?)}</sql-insert>
    <sql-delete callable="true">{? = call deletePerson (?)}</sql-delete>
    <sql-update callable="true">{? = call updatePerson (?, ?)}</sql-update>
</class>]]></programlisting>

        <para>
          The order of the positional parameters are currently vital, as they must be in 
          the same sequence as Hibernate expects them.
        </para>
        
        <para>
          You can see the expected order by enabling debug logging for the 
          <literal>org.hibernate.persister.entity</literal> level. With this level enabled 
          Hibernate will print out the static SQL that is used to create, update, delete etc. 
          entities. (To see the expected sequence, remember to not include your custom SQL in 
          the mapping files as that will override the Hibernate generated static sql.)
        </para>

        <para>
            The stored procedures are in most cases (read: better do it than not) required to
            return the number of rows inserted/updated/deleted, as Hibernate has some runtime
            checks for the success of the statement. Hibernate always registers the first statement
            parameter as a numeric output parameter for the CUD operations:
        </para>

        <programlisting><![CDATA[CREATE OR REPLACE FUNCTION updatePerson (uid IN NUMBER, uname IN VARCHAR2)
    RETURN NUMBER IS
BEGIN

    update PERSON
    set
        NAME = uname,
    where
        ID = uid;

    return SQL%ROWCOUNT;

END updatePerson;]]></programlisting>

        
    </sect1>

    <sect1 id="querysql-load">
        <title>Custom SQL for loading</title>

        <para>
            You may also declare your own SQL (or HQL) queries for entity loading:
        </para>

        <programlisting><![CDATA[<sql-query name="person">
    <return alias="pers" class="Person" lock-mode="upgrade"/>
    SELECT NAME AS {pers.name}, ID AS {pers.id} 
    FROM PERSON 
    WHERE ID=? 
    FOR UPDATE
</sql-query>]]></programlisting>

        <para>
            This is just a named query declaration, as discussed earlier. You may 
            reference this named query in a class mapping:
        </para>

        <programlisting><![CDATA[<class name="Person">
    <id name="id">
        <generator class="increment"/>
    </id>
    <property name="name" not-null="true"/>
    <loader query-ref="person"/>
</class>]]></programlisting>
    
        <para>
            This even works with stored procedures.
        </para>

        <para>
            You may even define a query for collection loading:
        </para>

<programlisting><![CDATA[<set name="employments" inverse="true">
    <key/>
    <one-to-many class="Employment"/>
    <loader query-ref="employments"/>
</set>]]></programlisting>
		
        <programlisting><![CDATA[<sql-query name="employments">
    <load-collection alias="emp" role="Person.employments"/>
    SELECT {emp.*}
    FROM EMPLOYMENT emp
    WHERE EMPLOYER = :id
    ORDER BY STARTDATE ASC, EMPLOYEE ASC
</sql-query>]]></programlisting>

        <para>
            You could even define an entity loader that loads a collection by
            join fetching:
        </para>

        <programlisting><![CDATA[<sql-query name="person">
    <return alias="pers" class="Person"/>
    <return-join alias="emp" property="pers.employments"/> 
    SELECT NAME AS {pers.*}, {emp.*}
    FROM PERSON pers
    LEFT OUTER JOIN EMPLOYMENT emp 
        ON pers.ID = emp.PERSON_ID
    WHERE ID=?
</sql-query>]]></programlisting>

    </sect1>

</chapter>