Chapter 6. Persistence
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## Chapter 6. Persistence

### Note

OpenJPA also includes the `OpenJPAPersistence` helper class to provide additional utility methods.

Within a container, you will typically use injection to access an `EntityManagerFactory`. Applications operating outside of a container, however, can use the `Persistence` class to obtain `EntityManagerFactory` objects in a vendor-neutral fashion.

    public static EntityManagerFactory createEntityManagerFactory(String name);
    public static EntityManagerFactory createEntityManagerFactory(String name, Map props);
    public static PersistenceUtil getPersistenceUtil();

Each `createEntityManagerFactory` method searches the system for an `EntityManagerFactory` definition with the given name. Use `null` for an unnamed factory. The optional map contains vendor-specific property settings used to further configure the factory.

`persistence.xml` files define `EntityManagerFactories`. The `createEntityManagerFactory` methods search for `persistence.xml` files within the `META-INF` directory of any `CLASSPATH` element. For example, if your `CLASSPATH` contains the `conf` directory, you could place an `EntityManagerFactory` definition in `conf/META-INF/persistence.xml`.

The `getPersistenceUtil` method returns a PersistenceUtil interface that can be used to determine whether an entity or attribute of an entity is loaded.

    PersistenceUtil pUtil = Persistence.getPersistenceUtil();

    if (!pUtil.isLoaded(myEntity)) {
        loadEntity(myEntity);
    }

## 1. persistence.xml

With the introduction of JPA 2.0, there are two versions of the `persistence.xml`. The most current revision of the 2.0 persistence schema is presented below. Version 1.0 of the persistence schema can be found at http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd.

    <?xml version="1.0" encoding="UTF-8"?>
        <!-- persistence.xml schema -->
    <xsd:schema targetNamespace="http://java.sun.com/xml/ns/persistence"
        xmlns:xsd="http://www.w3.org/2001/XMLSchema"
        xmlns:persistence="http://java.sun.com/xml/ns/persistence"
        elementFormDefault="qualified" attributeFormDefault="unqualified"
        version="2.0">

        <xsd:annotation>
            <xsd:documentation>
                @(#)persistence_2_0.xsd 1.0 October 1 2009
            </xsd:documentation>
        </xsd:annotation>

        <xsd:annotation>
            <xsd:documentation>

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              The contents of this file are subject to the terms of either the
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              option applies only if the new code is made subject to such
              option by the copyright holder.

            </xsd:documentation>
        </xsd:annotation>

        <xsd:annotation>
            <xsd:documentation>
            <![CDATA[
                This is the XML Schema for the persistence configuration file.
                The file must be named "META-INF/persistence.xml" in the
                persistence archive.
                Persistence configuration files must indicate
                the persistence schema by using the persistence namespace:
                http://java.sun.com/xml/ns/persistence
                and indicate the version of the schema by
                using the version element as shown below:
                <persistence xmlns="http://java.sun.com/xml/ns/persistence"
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
                http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
                version="2.0">
                ...
                </persistence>
            ]]>
            </xsd:documentation>
        </xsd:annotation>

        <xsd:simpleType name="versionType">
            <xsd:restriction base="xsd:token">
                <xsd:pattern value="[0-9]+(\.[0-9]+)*" />
            </xsd:restriction>
        </xsd:simpleType>
        <!-- **************************************************** -->
        <xsd:element name="persistence">
            <xsd:complexType>
                <xsd:sequence>
                    <!-- **************************************************** -->
                    <xsd:element name="persistence-unit"
                        minOccurs="1" maxOccurs="unbounded">
                        <xsd:complexType>
                            <xsd:annotation>
                                <xsd:documentation>
                                    Configuration of a persistence unit.
                                </xsd:documentation>
                            </xsd:annotation>
                            <xsd:sequence>
                                <!-- **************************************************** -->
                                <xsd:element name="description"
                                    type="xsd:string" minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            Description of this persistence unit.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="provider"
                                    type="xsd:string" minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            Provider class that supplies EntityManagers for this
                                            persistence unit.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="jta-data-source"
                                    type="xsd:string" minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            The container-specific name of the JTA datasource to use.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="non-jta-data-source"
                                    type="xsd:string" minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            The container-specific name of a non-JTA datasource to use.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="mapping-file"
                                    type="xsd:string" minOccurs="0"
                                    maxOccurs="unbounded">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            File containing mapping information. Loaded as a resource
                                            by the persistence provider.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="jar-file"
                                    type="xsd:string" minOccurs="0"
                                    maxOccurs="unbounded">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            Jar file that is to be scanned for managed classes.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="class" type="xsd:string"
                                    minOccurs="0" maxOccurs="unbounded">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            Managed class to be included in the persistence unit and
                                            to scan for annotations. It should be annotated
                                            with either @Entity, @Embeddable or @MappedSuperclass.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="exclude-unlisted-classes"
                                    type="xsd:boolean" default="true"
                                    minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            When set to true then only listed classes and jars will
                                            be scanned for persistent classes, otherwise the
                                            enclosing jar or directory will also be scanned.
                                            Not applicable to Java SE persistence units.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="shared-cache-mode"
                                    type="persistence:persistence-unit-caching-type"
                                    minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            Defines whether caching is enabled for the
                                            persistence unit if caching is supported by the
                                            persistence provider. When set to ALL, all entities
                                            will be cached. When set to NONE, no entities will
                                            be cached. When set to ENABLE_SELECTIVE, only entities
                                            specified as cacheable will be cached. When set to
                                            DISABLE_SELECTIVE, entities specified as not cacheable
                                            will not be cached. When not specified or when set to
                                            UNSPECIFIED, provider defaults may apply.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="validation-mode"
                                    type="persistence:persistence-unit-validation-mode-type"
                                    minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            The validation mode to be used for the persistence unit.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                </xsd:element>
                                <!-- **************************************************** -->
                                <xsd:element name="properties"
                                    minOccurs="0">
                                    <xsd:annotation>
                                        <xsd:documentation>
                                            A list of standard and vendor-specific properties
                                            and hints.
                                        </xsd:documentation>
                                    </xsd:annotation>
                                    <xsd:complexType>
                                        <xsd:sequence>
                                            <xsd:element name="property"
                                                minOccurs="0" maxOccurs="unbounded">
                                                <xsd:annotation>
                                                    <xsd:documentation>
                                                        A name-value pair.
                                                    </xsd:documentation>
                                                </xsd:annotation>
                                                <xsd:complexType>
                                                    <xsd:attribute
                                                        name="name" type="xsd:string"
                                                        use="required" />
                                                    <xsd:attribute
                                                        name="value" type="xsd:string"
                                                        use="required" />
                                                </xsd:complexType>
                                            </xsd:element>
                                        </xsd:sequence>
                                    </xsd:complexType>
                                </xsd:element>
                            </xsd:sequence>
                            <!-- **************************************************** -->
                            <xsd:attribute name="name" type="xsd:string"
                                use="required">
                                <xsd:annotation>
                                    <xsd:documentation>
                                        Name used in code to reference this persistence unit.
                                    </xsd:documentation>
                                </xsd:annotation>
                            </xsd:attribute>
                            <!-- **************************************************** -->
                            <xsd:attribute name="transaction-type"
                                type="persistence:persistence-unit-transaction-type">
                                <xsd:annotation>
                                    <xsd:documentation>
                                        Type of transactions used by EntityManagers from this
                                        persistence unit.
                                    </xsd:documentation>
                                </xsd:annotation>
                            </xsd:attribute>
                        </xsd:complexType>
                    </xsd:element>
                </xsd:sequence>
                <xsd:attribute name="version" type="persistence:versionType"
                    fixed="2.0" use="required" />
            </xsd:complexType>
        </xsd:element>
        <!-- **************************************************** -->
        <xsd:simpleType name="persistence-unit-transaction-type">
            <xsd:annotation>
                <xsd:documentation>
                    public enum PersistenceUnitTransactionType {JTA, RESOURCE_LOCAL};
                </xsd:documentation>
            </xsd:annotation>
            <xsd:restriction base="xsd:token">
                <xsd:enumeration value="JTA" />
                <xsd:enumeration value="RESOURCE_LOCAL" />
            </xsd:restriction>
        </xsd:simpleType>
        <!-- **************************************************** -->
        <xsd:simpleType name="persistence-unit-caching-type">
            <xsd:annotation>
                <xsd:documentation>
                    public enum SharedCacheMode { ALL, NONE, ENABLE_SELECTIVE,
                    DISABLE_SELECTIVE, UNSPECIFIED};
                </xsd:documentation>
            </xsd:annotation>
            <xsd:restriction base="xsd:token">
                <xsd:enumeration value="ALL" />
                <xsd:enumeration value="NONE" />
                <xsd:enumeration value="ENABLE_SELECTIVE" />
                <xsd:enumeration value="DISABLE_SELECTIVE" />
                <xsd:enumeration value="UNSPECIFIED" />
            </xsd:restriction>
        </xsd:simpleType>
        <!-- **************************************************** -->
        <xsd:simpleType name="persistence-unit-validation-mode-type">
            <xsd:annotation>
                <xsd:documentation>
                    public enum ValidationMode { AUTO, CALLBACK, NONE};
                </xsd:documentation>
            </xsd:annotation>
            <xsd:restriction base="xsd:token">
                <xsd:enumeration value="AUTO" />
                <xsd:enumeration value="CALLBACK" />
                <xsd:enumeration value="NONE" />
            </xsd:restriction>
        </xsd:simpleType>
    </xsd:schema>

The root element of a `persistence.xml` file is `persistence`, which then contains one or more `persistence-unit` definitions. The root element should include the version attribute with the appropriate version, `1.0` for a version 1.0 file and `2.0` for a version 2.0 file. Each persistence unit describes the configuration for the entity managers created by the persistence unit's entity manager factory. The persistence unit can specify these elements and attributes.

- `name`: This is the name you pass to the `Persistence.createEntityManagerFactory` methods described above. The name attribute is required.

- `transaction-type`: Whether to use managed (`JTA`) or local (`RESOURCE_LOCAL`) transaction management.

- `provider`: If you are using a third-party JPA vendor, this element names its implementation of the `PersistenceProvider` bootstrapping interface.

  ### Note

  Set the `provider` to `org.apache.openjpa.persistence.PersistenceProviderImpl` to use OpenJPA.

- `jta-data-source`: The JNDI name of a JDBC `DataSource` that is automatically enlisted in JTA transactions. This may be an XA `DataSource`.

- `non-jta-data-source`: The JNDI name of a JDBC `DataSource` that is not enlisted in JTA transactions.

- `mapping-file`*: The resource names of XML mapping files for entities and embeddable classes. You can also specify mapping information in an `orm.xml` file in your `META-INF` directory. If present, the `orm.xml` mapping file will be read automatically.

- `jar-file`*: The names of jar files containing entities and embeddable classes. The implementation will scan the jar for annotated classes.

- `class`*: The class names of entities and embeddable classes.

- `properties`: This element contains nested `property` elements used to specify vendor-specific settings. Each `property` has a name attribute and a value attribute.

  ### Note

  The Reference Guide's Chapter 2, Configuration describes OpenJPA's configuration properties.

Here is a typical `persistence.xml` file for a non-EE environment:

Example 6.1. persistence.xml

    <?xml version="1.0"?>
    <persistence version="1.0">
      <persistence-unit name="openjpa">
        <provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
        <class>tutorial.Animal</class>
        <class>tutorial.Dog</class>
        <class>tutorial.Rabbit</class>
        <class>tutorial.Snake</class>
        <properties>
          <property name="openjpa.ConnectionURL" value="jdbc:hsqldb:tutorial_database"/>
          <property name="openjpa.ConnectionDriverName" value="org.hsqldb.jdbcDriver"/>
          <property name="openjpa.ConnectionUserName" value="sa"/>
          <property name="openjpa.ConnectionPassword" value=""/>
          <property name="openjpa.Log" value="DefaultLevel=WARN, Tool=INFO"/>
        </properties>
      </persistence-unit>
    </persistence>

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