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Access multiple Databases in JPA

According to JPA specification we can define multiple "persistence-unit" elements (i.e. like below) in persistence.xml file and can easily refer them inside Dao layers as this.

public class PolarDaoImpl {

    @PersistenceContext(unitName="PolarPU")
    protected EntityManager entityManager;

--
}


public class BearDaoImpl {

    @PersistenceContext(unitName="BearPU")
    protected EntityManager entityManager;

--
}




Checkout sample persistence.xml



<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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">
    <!-- Database 1 -->
    <persistence-unit name="PolarPU" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <non-jta-data-source/>
        <class>com.cisco.polar.entity.ManagedAcademy</class>
        <class>com.cisco.polar.entity.TeachAcademy</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <properties>
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/polar"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value=""/>
        </properties>
    </persistence-unit>
    <!-- Database 2 -->
    <persistence-unit name="BearPU" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <non-jta-data-source/>
        <class>com.cisco.polar.entity.AcademyReportDate</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <properties>
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/bear"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value=""/>
        </properties>
    </persistence-unit>
</persistence>

Comments

andy said…
You can only access databases of type RDBMS in that way with your current provider. You'd have to go to a more advanced provider if you wanted to access data in RDBMS, or XML, or Excel, or LDAP etc ... such as DataNucleus
December 16, 2010 at 9:01 AM
andy said…
You can only access databases of type RDBMS in that way with your current provider. You'd have to go to a more advanced provider if you wanted to access data in RDBMS, or XML, or Excel, or LDAP etc ... such as DataNucleus
December 16, 2010 at 9:02 AM
Anonymous said…
hi intesar
I am looking for some help on establishing a holiday rental portal using liferay. it is all setup and running. are you free to help with the project?

thanks

salim
January 29, 2011 at 4:37 AM
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