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I need two or more than two connections in my web application using jpa

Alex Salauyou
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Rahul Singh
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  • are you talking about multiple data sources? Because DB connections and data sources are quite different terms. – Ish Oct 21 '15 at 11:09
  • two data sources like both will be a oracle database but the crdentials sid and all will be different for the two data sources – Rahul Singh Oct 21 '15 at 11:12

2 Answers2

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To use different data sources, add multiple persistence units (say, source-1 and source-2 in persistence.xml and create multiple EntityManagerFactoryes by name):

EntityManagerFactory emf1 = Persistence.createEntityManagerFactory("source-1");
EntityManagerFactory emf2 = Persistence.createEntityManagerFactory("source-2");

or, if you're working on Spring or Java EE application server, inject them by name also:

@PersistenceUnit(name = "source-1")
EntityManagerFactory emf1;

@PersistenceContext(unitName = "source-2") // as an option
EntityManager em2;

persistence.xml will thus look like the following:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">

    <persistence-unit name="source-1" transaction-type="RESOURCE_LOCAL">
        <properties>
            <!-- source-1 properties here -->
        </properties>
    </persistence-unit>

    <persistence-unit name="source-2" transaction-type="RESOURCE_LOCAL">
        <properties>
            <!-- source-2 properties here -->
        </properties>
    </persistence-unit>
</persistence>

Example of how to configure persistence unit, create EntityManager to manage entities and execute queries can be found here.

Alex Salauyou
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    Can you please share a example of such as i m new to this concept and not able to decide what to do – Rahul Singh Oct 21 '15 at 11:15
  • it is telling muliplt persistence unit defined only the first persistence unit will be identified – Rahul Singh Oct 21 '15 at 11:20
  • @RahulSingh Hibernate will define all persistence units listed in `persistence.xml`, tested many times. Please see this post: http://stackoverflow.com/questions/5356152/two-persistence-unit-in-one-persistence-xml – Alex Salauyou Oct 21 '15 at 11:25
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For single datasource jpa will use multiple connections internally.So you don't need to do anything.

Sainik Kumar Singhal
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  • The question is not about connections to the same database,but to multiple different DBs. Though, I understand that the wording in the question is confusing – OndroMih Oct 22 '15 at 16:23