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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
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
Salim 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

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