You can use OpenJPA with any third-party javax.sql.DataSource
. There are multiple ways of telling OpenJPA about a
DataSource:
Set the DataSource into the map passed to
Persistence.createEntityManagerFactory under the
openjpa.ConnectionFactory
key.
Bind the DataSource into JNDI, and then specify its
location in the jta-data-source or
non-jta-data-source element of the
JPA XML format (depending on
whether the DataSource is managed by JTA), or in the
openjpa.ConnectionFactoryName property.
Specify the full class name of the DataSource
implementation in the
openjpa.ConnectionDriverName property in place of a JDBC
driver. In this configuration OpenJPA will instantiate an instance of the named
class via reflection. It will then configure the DataSource
with the properties in the
openjpa.ConnectionProperties setting.
The features of OpenJPA's own DataSource can
also be used with third-party implementations. OpenJPA layers on top of the
third-party DataSource to provide the extra
functionality. To configure these features use the
openjpa.ConnectionFactoryProperties property described
in the previous section.
Example 4.2. Properties File for a Third-Party DataSource
<property name="openjpa.ConnectionDriverName" value="oracle.jdbc.pool.OracleDataSource"/>
<property name="openjpa.ConnectionProperties"
value="PortNumber=1521, ServerName=saturn, DatabaseName=solarsid, DriverType=thin"/>
<property name="openjpa.ConnectionFactoryProperties" value="QueryTimeout=5000"/>
Certain application servers automatically enlist their DataSource
s in global transactions. When this is the case, OpenJPA should not
attempt to commit the underlying connection, leaving JDBC transaction completion
to the application server. To notify OpenJPA that your third-party
DataSource is managed by the application server, use the
jta-data-source element of your
persistence.xml file or set the
openjpa.ConnectionFactoryMode property to
managed.
Note that OpenJPA can only use managed DataSources when
it is also integrating with the application server's managed transactions. Also
note that all XA DataSources are enlisted, and you must
set this property when using any XA DataSource.
When using a managed DataSource, you should also
configure a second unmanaged DataSource that OpenJPA can
use to perform tasks that are independent of the global transaction. The most
common of these tasks is updating the sequence table OpenJPA uses to generate
unique primary key values for your datastore identity objects. Configure the
second DataSource using the non-jta-data-source
persistence.xml element, or OpenJPA's various
"2" connection properties, such as openjpa.ConnectionFactory2Name
or openjpa.Connection2DriverName. These
properties are outlined in Chapter 2,
Configuration
.
Example 4.3. Managed DataSource Configuration
<!-- managed DataSource -->
<jta-data-source>java:/OracleXASource</jta-data-source>
<properties>
<!-- use OpenJPA's built-in DataSource for unmanaged connections -->
<property name="openjpa.Connection2UserName" value="scott"/>
<property name="openjpa.Connection2Password" value="tiger"/>
<property name="openjpa.Connection2URL" value="jdbc:oracle:thin:@CROM:1521:OpenJPADB"/>
<property name="openjpa.Connection2DriverName" value="oracle.jdbc.driver.OracleDriver"/>
</properties>
As mentioned above, the JTA and Non-JTA DataSources may be passed in as configuration properties
at EntityManagerFactory creation. Either the JPA standard properties (
javax.persistence.jtaDataSource, java.persistence.nonJtaDataSource)
or their OpenJPA specific equivalents (openjpa.ConnectionFactoryName,
openjpa.ConnectionFactory2Name) may be used. One usecase for this function is to
store production connection information in configuration files but override the value when testing.
Example 4.4.
Map<Object,Object> props = new HashMap<Object,Object>();
props.put("javax.persistence.jtaDataSource", "jdbc/myDataSource");
props.put("javax.persistence.nonJtaDataSource", "jdbc/myNonJTADataSource");
emf = Persistence.createEntityManagerFactory("example", props);
The JPA specification allows the DataSource (ConnectionFactory) to be specified on the EntityManagerFactory.OpenJPA extends this support and allows each EntityManager to override the DataSource from the EntityManagerFactory. It's expected that the EntityManagerFactory will also be configured with a valid jta / nonJta DataSource. The DataSource configured on the EntityManagerFactory will be used to obtain a DBDictionary and (rarely) to gather some information about the database in use (e.g. version, JDBC driver version).
If the EntityManagerFactory is not configured with a valid DataSource there are a few additional caveats.
The openjpa.DBDictionary property must be
used to ensure the correct DBDictionary is used.
OpenJPA will always attempt to obtain a datasource from JNDI based on the configuration for the EntityManagerFactory. When a JNDI name is specified on the EntityManager this lookup happens slightly earlier than normal. If the lookup fails the JNDI name provided at EntityManager creation will be set into the EntityManagerFactory's configuration and used in subsequent attempts.
In effect this option allows a single set of entity definitions to be shared between multiple database instances or schemas within an instance. This can be highly beneficial when there are a large number of entity definitions (e.g. > 200), or a large number of databases / schemas in use.
The same database type and version must be used by each EntityManager. OpenJPA will use the same DBDictionary for each EntityManager and will make no attempt to alter SQL syntax between EntityManager instances.
It is the application's responsibility to ensure that the schema is identical on each database.
The application may not specify schema names for individual entities.
The DataSource (ConnectionFactory) name may only be specified when the EntityManager is created. The datasource may not be switched while an EntityManager is in use.
The L2 cache (DataCache) should not be used if different DataSources are specified for each EntityManager
SynchronizeMappings should not be used with this feature.
Table and Sequence generators should not be used with this feature.
It is not required, but is recommended that the
openjpa.DBDictionary property be specified when
using this feature
If a JTA DataSource is not available when the EntityManager is created an
ArgumentException will be thrown.
The EntityManager will not fall back on the JTA DataSource defined in the
configuration.
The same logic applies if a Non-JTA DataSource is not available when the EntityManager is created. OpenJPA will not fall back to the configured non-JTA DataSource.