620 lines
18 KiB
XML
620 lines
18 KiB
XML
<chapter id="example-mappings">
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<title>Example: Various Mappings</title>
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<para>
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This chapters shows off some more complex association mappings.
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</para>
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<sect1 id="example-mappings-emp">
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<title>Employer/Employee</title>
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<para>
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The following model of the relationship between <literal>Employer</literal> and
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<literal>Employee</literal> uses an actual entity class (<literal>Employment</literal>)
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to represent the association. This is done because there might be more than one
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period of employment for the same two parties. Components are used to model monetary
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values and employee names.
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</para>
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<mediaobject>
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<imageobject role="fo">
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<imagedata fileref="images/EmployerEmployee.gif" format="GIF" align="center"/>
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</imageobject>
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<imageobject role="html">
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<imagedata fileref="../shared/images/EmployerEmployee.gif" format="GIF" align="center"/>
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</imageobject>
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</mediaobject>
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<para>
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Heres a possible mapping document:
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</para>
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<programlisting><![CDATA[<hibernate-mapping>
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<class name="Employer" table="employers">
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<id name="id">
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<generator class="sequence">
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<param name="sequence">employer_id_seq</param>
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</generator>
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</id>
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<property name="name"/>
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</class>
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<class name="Employment" table="employment_periods">
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<id name="id">
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<generator class="sequence">
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<param name="sequence">employment_id_seq</param>
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</generator>
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</id>
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<property name="startDate" column="start_date"/>
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<property name="endDate" column="end_date"/>
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<component name="hourlyRate" class="MonetaryAmount">
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<property name="amount">
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<column name="hourly_rate" sql-type="NUMERIC(12, 2)"/>
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</property>
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<property name="currency" length="12"/>
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</component>
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<many-to-one name="employer" column="employer_id" not-null="true"/>
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<many-to-one name="employee" column="employee_id" not-null="true"/>
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</class>
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<class name="Employee" table="employees">
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<id name="id">
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<generator class="sequence">
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<param name="sequence">employee_id_seq</param>
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</generator>
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</id>
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<property name="taxfileNumber"/>
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<component name="name" class="Name">
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<property name="firstName"/>
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<property name="initial"/>
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<property name="lastName"/>
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</component>
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</class>
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</hibernate-mapping>]]></programlisting>
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<para>
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And heres the table schema generated by <literal>SchemaExport</literal>.
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</para>
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<programlisting><![CDATA[create table employers (
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id BIGINT not null,
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name VARCHAR(255),
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primary key (id)
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)
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create table employment_periods (
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id BIGINT not null,
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hourly_rate NUMERIC(12, 2),
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currency VARCHAR(12),
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employee_id BIGINT not null,
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employer_id BIGINT not null,
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end_date TIMESTAMP,
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start_date TIMESTAMP,
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primary key (id)
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)
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create table employees (
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id BIGINT not null,
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firstName VARCHAR(255),
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initial CHAR(1),
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lastName VARCHAR(255),
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taxfileNumber VARCHAR(255),
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primary key (id)
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)
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alter table employment_periods
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add constraint employment_periodsFK0 foreign key (employer_id) references employers
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alter table employment_periods
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add constraint employment_periodsFK1 foreign key (employee_id) references employees
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create sequence employee_id_seq
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create sequence employment_id_seq
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create sequence employer_id_seq]]></programlisting>
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</sect1>
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<sect1 id="example-mappings-authorwork">
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<title>Author/Work</title>
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<para>
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Consider the following model of the relationships between <literal>Work</literal>,
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<literal>Author</literal> and <literal>Person</literal>. We represent the relationship
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between <literal>Work</literal> and <literal>Author</literal> as a many-to-many
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association. We choose to represent the relationship between <literal>Author</literal>
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and <literal>Person</literal> as one-to-one association. Another possibility would be to
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have <literal>Author</literal> extend <literal>Person</literal>.
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</para>
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<mediaobject>
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<imageobject role="fo">
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<imagedata fileref="images/AuthorWork.gif" format="GIF" align="center"/>
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</imageobject>
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<imageobject role="html">
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<imagedata fileref="../shared/images/AuthorWork.gif" format="GIF" align="center"/>
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</imageobject>
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</mediaobject>
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<para>
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The following mapping document correctly represents these relationships:
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</para>
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<programlisting><![CDATA[<hibernate-mapping>
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<class name="Work" table="works" discriminator-value="W">
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<id name="id" column="id">
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<generator class="native"/>
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</id>
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<discriminator column="type" type="character"/>
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<property name="title"/>
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<set name="authors" table="author_work">
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<key column name="work_id"/>
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<many-to-many class="Author" column name="author_id"/>
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</set>
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<subclass name="Book" discriminator-value="B">
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<property name="text"/>
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</subclass>
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<subclass name="Song" discriminator-value="S">
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<property name="tempo"/>
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<property name="genre"/>
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</subclass>
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</class>
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<class name="Author" table="authors">
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<id name="id" column="id">
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<!-- The Author must have the same identifier as the Person -->
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<generator class="assigned"/>
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</id>
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<property name="alias"/>
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<one-to-one name="person" constrained="true"/>
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<set name="works" table="author_work" inverse="true">
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<key column="author_id"/>
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<many-to-many class="Work" column="work_id"/>
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</set>
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</class>
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<class name="Person" table="persons">
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<id name="id" column="id">
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<generator class="native"/>
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</id>
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<property name="name"/>
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</class>
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</hibernate-mapping>]]></programlisting>
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<para>
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There are four tables in this mapping. <literal>works</literal>,
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<literal>authors</literal> and <literal>persons</literal> hold work, author
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and person data respectively. <literal>author_work</literal> is an association
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table linking authors to works. Heres the table schema, as generated by
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<literal>SchemaExport</literal>.
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</para>
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<programlisting><![CDATA[create table works (
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id BIGINT not null generated by default as identity,
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tempo FLOAT,
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genre VARCHAR(255),
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text INTEGER,
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title VARCHAR(255),
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type CHAR(1) not null,
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primary key (id)
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)
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create table author_work (
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author_id BIGINT not null,
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work_id BIGINT not null,
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primary key (work_id, author_id)
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)
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create table authors (
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id BIGINT not null generated by default as identity,
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alias VARCHAR(255),
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primary key (id)
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)
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create table persons (
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id BIGINT not null generated by default as identity,
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name VARCHAR(255),
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primary key (id)
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)
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alter table authors
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add constraint authorsFK0 foreign key (id) references persons
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alter table author_work
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add constraint author_workFK0 foreign key (author_id) references authors
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alter table author_work
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add constraint author_workFK1 foreign key (work_id) references works]]></programlisting>
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</sect1>
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<sect1 id="example-mappings-customerorderproduct">
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<title>Customer/Order/Product</title>
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<para>
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Now consider a model of the relationships between <literal>Customer</literal>,
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<literal>Order</literal> and <literal>LineItem</literal> and <literal>Product</literal>.
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There is a one-to-many association between <literal>Customer</literal> and
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<literal>Order</literal>, but how should we represent <literal>Order</literal> /
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<literal>LineItem</literal> / <literal>Product</literal>? I've chosen to map
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<literal>LineItem</literal> as an association class representing the many-to-many
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association between <literal>Order</literal> and <literal>Product</literal>. In
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Hibernate, this is called a composite element.
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</para>
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<mediaobject>
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<imageobject role="fo">
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<imagedata fileref="images/CustomerOrderProduct.gif" format="GIF" align="center"/>
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</imageobject>
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<imageobject role="html">
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<imagedata fileref="../shared/images/CustomerOrderProduct.gif" format="GIF" align="center"/>
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</imageobject>
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</mediaobject>
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<para>
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The mapping document:
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</para>
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<programlisting><![CDATA[<hibernate-mapping>
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<class name="Customer" table="customers">
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<id name="id">
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<generator class="native"/>
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</id>
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<property name="name"/>
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<set name="orders" inverse="true">
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<key column="customer_id"/>
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<one-to-many class="Order"/>
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</set>
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</class>
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<class name="Order" table="orders">
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<id name="id">
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<generator class="native"/>
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</id>
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<property name="date"/>
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<many-to-one name="customer" column="customer_id"/>
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<list name="lineItems" table="line_items">
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<key column="order_id"/>
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<list-index column="line_number"/>
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<composite-element class="LineItem">
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<property name="quantity"/>
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<many-to-one name="product" column="product_id"/>
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</composite-element>
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</list>
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</class>
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<class name="Product" table="products">
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<id name="id">
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<generator class="native"/>
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</id>
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<property name="serialNumber"/>
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</class>
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</hibernate-mapping>]]></programlisting>
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<para>
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<literal>customers</literal>, <literal>orders</literal>, <literal>line_items</literal> and
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<literal>products</literal> hold customer, order, order line item and product data
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respectively. <literal>line_items</literal> also acts as an association table linking
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orders with products.
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</para>
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<programlisting><![CDATA[create table customers (
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id BIGINT not null generated by default as identity,
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name VARCHAR(255),
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primary key (id)
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)
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create table orders (
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id BIGINT not null generated by default as identity,
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customer_id BIGINT,
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date TIMESTAMP,
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primary key (id)
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)
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create table line_items (
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line_number INTEGER not null,
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order_id BIGINT not null,
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product_id BIGINT,
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quantity INTEGER,
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primary key (order_id, line_number)
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)
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create table products (
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id BIGINT not null generated by default as identity,
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serialNumber VARCHAR(255),
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primary key (id)
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)
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alter table orders
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add constraint ordersFK0 foreign key (customer_id) references customers
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alter table line_items
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add constraint line_itemsFK0 foreign key (product_id) references products
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alter table line_items
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add constraint line_itemsFK1 foreign key (order_id) references orders]]></programlisting>
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</sect1>
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<sect1 id="misc">
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<title>Miscellaneous example mappings</title>
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<para>
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These examples are all taken from the Hibernate test suite. You
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will find many other useful example mappings there. Have a look at the
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<literal>src</literal> folder of the Hibernate distribution.
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</para>
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<para>TODO: put words around this stuff</para>
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<sect2 id="example-mappings-typed-onetone">
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<title>"Typed" one-to-one association</title>
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<programlisting><![CDATA[<class name="Person">
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<id name="name"/>
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<one-to-one name="address"
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cascade="all">
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<formula>name</formula>
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<formula>'HOME'</formula>
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</one-to-one>
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<one-to-one name="mailingAddress"
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cascade="all">
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<formula>name</formula>
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<formula>'MAILING'</formula>
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</one-to-one>
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</class>
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<class name="Address" batch-size="2"
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check="addressType in ('MAILING', 'HOME', 'BUSINESS')">
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<composite-id>
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<key-many-to-one name="person"
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column="personName"/>
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<key-property name="type"
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column="addressType"/>
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</composite-id>
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<property name="street" type="text"/>
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<property name="state"/>
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<property name="zip"/>
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</class>]]></programlisting>
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</sect2>
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<sect2 id="example-mappings-composite-key">
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<title>Composite key example</title>
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<programlisting><![CDATA[<class name="Customer">
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<id name="customerId"
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length="10">
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<generator class="assigned"/>
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</id>
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<property name="name" not-null="true" length="100"/>
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<property name="address" not-null="true" length="200"/>
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<list name="orders"
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inverse="true"
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cascade="save-update">
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<key column="customerId"/>
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<index column="orderNumber"/>
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<one-to-many class="Order"/>
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</list>
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</class>
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<class name="Order" table="CustomerOrder" lazy="true">
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<synchronize table="LineItem"/>
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<synchronize table="Product"/>
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<composite-id name="id"
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class="Order$Id">
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<key-property name="customerId" length="10"/>
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<key-property name="orderNumber"/>
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</composite-id>
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<property name="orderDate"
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type="calendar_date"
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not-null="true"/>
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<property name="total">
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<formula>
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( select sum(li.quantity*p.price)
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from LineItem li, Product p
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where li.productId = p.productId
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and li.customerId = customerId
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and li.orderNumber = orderNumber )
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</formula>
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</property>
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<many-to-one name="customer"
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column="customerId"
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insert="false"
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update="false"
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not-null="true"/>
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<bag name="lineItems"
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fetch="join"
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inverse="true"
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cascade="save-update">
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<key>
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<column name="customerId"/>
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<column name="orderNumber"/>
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</key>
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<one-to-many class="LineItem"/>
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</bag>
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</class>
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<class name="LineItem">
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<composite-id name="id"
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class="LineItem$Id">
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<key-property name="customerId" length="10"/>
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<key-property name="orderNumber"/>
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<key-property name="productId" length="10"/>
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</composite-id>
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<property name="quantity"/>
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<many-to-one name="order"
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insert="false"
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update="false"
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not-null="true">
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<column name="customerId"/>
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<column name="orderNumber"/>
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</many-to-one>
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<many-to-one name="product"
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insert="false"
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update="false"
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not-null="true"
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column="productId"/>
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</class>
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<class name="Product">
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<synchronize table="LineItem"/>
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<id name="productId"
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length="10">
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<generator class="assigned"/>
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</id>
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<property name="description"
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not-null="true"
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length="200"/>
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<property name="price" length="3"/>
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<property name="numberAvailable"/>
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<property name="numberOrdered">
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<formula>
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( select sum(li.quantity)
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from LineItem li
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where li.productId = productId )
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</formula>
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</property>
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</class>]]></programlisting>
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</sect2>
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<sect2 id="example-mappings-content-discrimination">
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<title>Content based discrimination</title>
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<programlisting><![CDATA[<class name="Person"
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discriminator-value="P">
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<id name="id"
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column="person_id"
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unsaved-value="0">
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<generator class="native"/>
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</id>
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<discriminator
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type="character">
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<formula>
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case
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when title is not null then 'E'
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when salesperson is not null then 'C'
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else 'P'
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end
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</formula>
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</discriminator>
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<property name="name"
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not-null="true"
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length="80"/>
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<property name="sex"
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not-null="true"
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update="false"/>
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<component name="address">
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<property name="address"/>
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<property name="zip"/>
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<property name="country"/>
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</component>
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<subclass name="Employee"
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discriminator-value="E">
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<property name="title"
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length="20"/>
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<property name="salary"/>
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<many-to-one name="manager"/>
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</subclass>
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<subclass name="Customer"
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discriminator-value="C">
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<property name="comments"/>
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<many-to-one name="salesperson"/>
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</subclass>
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</class>]]></programlisting>
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</sect2>
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<sect2 id="example-mappings-association-alternatekeys" >
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<title>Associations on alternate keys</title>
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<programlisting><![CDATA[<class name="Person">
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<id name="id">
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<generator class="hilo"/>
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</id>
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<property name="name" length="100"/>
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<one-to-one name="address"
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property-ref="person"
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cascade="all"
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fetch="join"/>
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|
<set name="accounts"
|
|
inverse="true">
|
|
<key column="userId"
|
|
property-ref="userId"/>
|
|
<one-to-many class="Account"/>
|
|
</set>
|
|
|
|
<property name="userId" length="8"/>
|
|
|
|
</class>
|
|
|
|
<class name="Address">
|
|
|
|
<id name="id">
|
|
<generator class="hilo"/>
|
|
</id>
|
|
|
|
<property name="address" length="300"/>
|
|
<property name="zip" length="5"/>
|
|
<property name="country" length="25"/>
|
|
<many-to-one name="person" unique="true" not-null="true"/>
|
|
|
|
</class>
|
|
|
|
<class name="Account">
|
|
<id name="accountId" length="32">
|
|
<generator class="uuid.hex"/>
|
|
</id>
|
|
|
|
<many-to-one name="user"
|
|
column="userId"
|
|
property-ref="userId"/>
|
|
|
|
<property name="type" not-null="true"/>
|
|
|
|
</class>]]></programlisting>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
</chapter>
|
|
|