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EclipseLink/DesignDocs/328404

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Revision as of 14:36, 22 October 2010 by Andrei.ilitchev.oracle.com (Talk | contribs) (Config files)

Design Specification: Support SessionBroker in JPA

ER 328404

Document History

2010/10/22 Andrei Ilitchev Initial Version

Project overview

The goal is to allow for different classes contained in a single persistence context to be mapped to different databases.

em.persist(new A(..));
em.persist(new Z(..));
// insert A into db1; insert Z into db2:
// the two different data bases possibly from different vendors
em.flush();

Concepts

  • Currently each persistence unit has a single ServerSession.
    • ServerSession typically connected to a single data base.
      • Even though ServerSession may use connection pools that connected to different data bases these databases always should share the same database platform.
        • That means it's impossible to use ServerSession to map different classes to different types of data bases (say, Oracle and MySQL).
  • Eclipselink core defines SessionBroker class that aggregates several ServerSessions.
    • SessionBroker maps each class to a single ServerSession.
    • Each ServerSession connected to a different data base.
      • These ServerSessions are not required to share the same database platform.
      • Therefore different classes mapped to different data bases, too.
  • This feature is going to define persistence unit that has a SessionBroker instead of ServerSession.
    • Let's call Container persistence unit (or SessionBroker persistence unit).

Requirements

  • SessionBroker persistence unit must be defined in persistence.xml (as any other persistence unit).
  • The two main use cases:
    • Unify multiple persistence units (with independent from each other object models).
      • User starts with several independent persistence units, creates a new SessionBroker persistent unit that aggregates ServerSessions defined in the original persistence units.
      • The original persistence units remain unchanged, could still be used individually.
      • Limitation: the original persistence units and the SessionBroker persistent unit should be all defined in a single jar file.
    • Split single persistent unit.
      • User starts with a single persistence unit, alters it to become SessionBroker persistence unit.

Design Constraints

Design / Functionality

  • ServerSessions that are aggregated by a SessionBroker persistence unit are "invisible" outside of it:
    • don't have EntityManagerFactories associated with them;
    • EntityManagerSetupImpl used for their creation are not kept;
    • these sessions are not stored in SessionManager.

Testing

API

GUI

Config files

  • Proposed configuration of SessionBroker persistence unit is done entirely through Persistence Unit properties.
    • Properties extension usage and naming patterns.
// Property with set values
eclipselink.define.my-set-property.value1 -> ""
eclipselink.define.my-set-property.value2 -> ""
...
eclipselink.define.my-set-property.valueN -> ""
 
// Converted to a Set:
my-set-property = {value1, value2, ..., valueN};
 
 
// Property with Map value
eclipselink.define.my-map-property.value1.key1 -> ""
eclipselink.define.my-map-property.value2.key2 -> ""
...
eclipselink.define.my-map-property.valueN.keyN -> ""
 
// Converted to a Map:
my-property = {key1 -> value1; key2 -> value2; ..., keyN -> valueN};
 
// Suggested naming convention:
// let's use "eclipselink.define" prefix for these "value-less" properties.


  • The two main use cases:
    • Unify multiple persistence units (with independent from each other object models).

There are two predefine independent persistence units: puABC (that maps classes A, B, C) and puXYZ (that maps classes X, Y, Z). None of A, B, C classes references any of X, Y, Z classes and vise verse. Below are several examples of persistence.xml for SessionBroker persistence unit.

<!--Scenario 1 - simply use puABC and puXYZ exactly as they were originally defined-->
-<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 persistence_1_0.xsd" version="1.0">
    <persistence-unit name="broker" transaction-type="RESOURCE_LOCAL">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <properties>
	    <!--Note that puABC must exist and be defined in the same jar file with this persistence.xml-->
	    <property name="eclipselink.define.add-contained-pu.puABC" value=""/>
	    <!--Note that puXYZ must exist and be defined in the same jar file with this persistence.xml-->
	    <property name="eclipselink.define.add-contained-pu.puXYZ" value=""/>
        </properties>
    </persistence-unit>
</persistence>

The result is SessionBroker persistence unit named "broker" that aggregates two ServerSessions - one maps classes A, B, C; another - X, Y, Z.

<!--Scenario 2 - override some of the properies of puABC and puXYZ -->
-<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 persistence_1_0.xsd" version="1.0">
    <!-- note that there is no need to pass transaction type down to contained sessions - that will be done automatically -->
    <persistence-unit name="broker" transaction-type="JPA">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <properties>
            <!-- note that there is no need to pass server platform down to contained sessions - that will be done automatically -->
            <property name="eclipselink.target-server" value="WebLogic_10"/>
 
	    <!--Note that puABC must exist and be defined in the same jar file with this persistence.xml-->
	    <property name="eclipselink.define.add-contained-pu.puABC" value=""/>
	    <property name="javax.persistence.jtaDataSource.puABC" value="ElOracleJTA"/>
	    <property name="javax.persistence.nonjtaDataSource.puABC" value="ElOracle"/>
            <!-- Switching to data sources from user/password - has to remove user name-->
	    <property name="javax.persistence.jdbc.user.puABC" value=""/>
 
	    <!--Note that puXYZ must exist and be defined in the same jar file with this persistence.xml-->
	    <property name="eclipselink.define.add-contained-pu.puXYZ" value=""/>
	    <property name="javax.persistence.jtaDataSource.puXYZ" value="ElMySQLJTA"/>
	    <property name="javax.persistence.nonjtaDataSource.puXYZ" value="ElMySQL"/>
            <!-- Switching to data sources from user/password - has to remove user name-->
	    <property name="javax.persistence.jdbc.user.puXYZ" value=""/>
        </properties>
    </persistence-unit>
</persistence>

The result is SessionBroker persistence unit named "broker" that aggregates two ServerSessions - one maps classes A, B, C; another - X, Y, Z. The original connection parameters in both member sessions were substituted with the ones provided in SessionBroker properties.

    • Split single persistent unit.

There is a single predefined persistence unit: puABCXYZ (that maps classes A, B, C, X, Y, Z). There could be any sorts of references between the classes. Below is example that contains persistence.xml of the original persistence unit and for SessionBroker persistence unit.

<!--Original persistence unit -->
-<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 persistence_1_0.xsd" version="1.0">
    <persistence-unit name="puABCXYZ" transaction-type="RESOURCE_LOCAL">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
	    <property name="javax.persistence.jdbc.user" value="MyUser"/>
	    <property name="javax.persistence.jdbc.password" value="MyPassword"/>
            <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@qaott11.ca.oracle.com:1521:toplink"/>
        </properties>
    </persistence-unit>
</persistence>
<!--SessionBroker persistence unit -->
-<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 persistence_1_0.xsd" version="1.0">
    <persistence-unit name="puABCXYZ" transaction-type="RESOURCE_LOCAL">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
	    <property name="javax.persistence.jdbc.user" value="MyUser"/>
	    <property name="javax.persistence.jdbc.password" value="MyPassword"/>
            <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@qaott11.ca.oracle.com:1521:toplink"/>
 
	    <!--Note that puXYZ does not exist - it's used as an alias for the new ServerSession to be created-->
            <property name="eclipselink.define.split-contained-pu.puXYZ" value=""/>
            <!--either provide full class name-->
	    <property name="eclipselink.define.split-contained-pu-class.package.X" value=""/>
	    <property name="eclipselink.define.split-contained-pu-class.package.Y" value=""/>
            <!--or entity name-->
	    <property name="eclipselink.define.split-contained-pu-class.Z" value=""/>
	    <property name="javax.persistence.jdbc.user.puXYZ" value="MyUser2"/>
	    <property name="javax.persistence.jdbc.password.puXYZ" value="MyPassword2"/>
            <property name="javax.persistence.jdbc.driver.puXYZ" value="com.mysql.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url.puXYZ" value="jdbc:mysql://qaott51.ca.oracle.com:3306/MyUser2"/>
        </properties>
    </persistence-unit>
</persistence>

The result is SessionBroker persistence unit that aggregates two ServerSessions - one maps classes A, B, C; another - X, Y, Z. The ServerSession that maps classes X, Y, Z is created using all the properties defined in the persistence unit, overriding with the values designated to puXYZ. For all the remaining classes (in this case A, B, C) the ServerSession is created with all the original properties.

  • Mix the two main use cases.

Let's create a SessionBroker persistence unit from original puABC, by splitting class C and adding puXYZ. Below is example that contains persistence.xml of the original persistence unit and for SessionBroker persistence unit.

<!--Original persistence unit -->
-<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 persistence_1_0.xsd" version="1.0">
    <persistence-unit name="puABC" transaction-type="RESOURCE_LOCAL">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <class>A</class>
        <class>B</class>
        <class>C</class>
        <properties>
	    <property name="javax.persistence.jdbc.user" value="MyUser"/>
	    <property name="javax.persistence.jdbc.password" value="MyPassword"/>
            <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@qaott11.ca.oracle.com:1521:toplink"/>
        </properties>
    </persistence-unit>
</persistence>
<!--SessionBroker persistence unit -->
-<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 persistence_1_0.xsd" version="1.0">
    <persistence-unit name="puABCXYZ" transaction-type="RESOURCE_LOCAL">
        <provider>
            org.eclipse.persistence.jpa.PersistenceProvider
        </provider>
        <class>A</class>
        <class>B</class>
        <class>C</class>
        <properties>
	    <property name="javax.persistence.jdbc.user" value="MyUser"/>
	    <property name="javax.persistence.jdbc.password" value="MyPassword"/>
            <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@qaott11.ca.oracle.com:1521:toplink"/>
 
	    <!--Note that puC does not exist - it's used as an alias for the new ServerSession to be created-->
            <property name="eclipselink.define.split-contained-pu.puC" value=""/>
            <!--either provide full class name or entity name-->
	    <property name="eclipselink.define.split-contained-pu-class.C" value=""/>
	    <property name="javax.persistence.jdbc.user.puC" value="MyUser2"/>
	    <property name="javax.persistence.jdbc.password.puC" value="MyPassword2"/>
            <property name="javax.persistence.jdbc.driver.puC" value="com.mysql.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url.puC" value="jdbc:mysql://qaott51.ca.oracle.com:3306/MyUser2"/>
 
	    <!--Note that puXYZ must exist and be defined in the same jar file with this persistence.xml-->
	    <property name="eclipselink.define.add-contained-pu.puXYZ" value=""/>
        </properties>
    </persistence-unit>
</persistence>

The result is SessionBroker persistence unit that aggregates three ServerSessions - one maps classes A, B; another - C; yet another - X, Y, Z. The ServerSession that maps classes X, Y, Z is created using puXYZ. The ServerSession that maps class C is created using all the properties defined in the persistence unit, overriding with the values designated to puC. For all the remaining classes (in this case A and B) the ServerSession is created with all the original properties.

Documentation

Open Issues

This section lists the open issues that are still pending that must be decided prior to fully implementing this project's requirements.

Issue # Owner Description / Notes

Decisions

This section lists decisions made. These are intended to document the resolution of open issues or constraints added to the project that are important.

Issue # Description / Notes Decision

Future Considerations

During the research for this project the following items were identified as out of scope but are captured here as potential future enhancements. If agreed upon during the review process these should be logged in the bug system.

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