MySQL Persistence.xml - SQL

If you are working with JPA (Java Persistence API) or Hibernate, then you are probably familiar with the persistence.xml file. This file is responsible for configuring the persistence unit for your application, specifying the database connection details, and providing other information for JPA/Hibernate to work properly.

In this article, we will focus on configuring the persistence.xml file for MySQL databases and SQL queries.

Setting Up the Persistence Unit

To start, we need to create a new persistence.xml file in our project's META-INF folder. The content of this file will vary depending on your application's requirements, but it should contain the following elements:

<?xml version="1.0" encoding="UTF-8"?>
<persistence 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_2.xsd"
             version="2.2">
 
    <persistence-unit name="my-persistence-unit" transaction-type="JTA">
        <jta-data-source>java:/mydatasource</jta-data-source>
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <class>com.example.User</class>
        <exclude-unlisted-classes>true</exclude-unlisted-classes>
        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL8Dialect"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/mydb"/>
            <property name="hibernate.connection.username" value="dbuser"/>
            <property name="hibernate.connection.password" value="dbpassword"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
 
</persistence>

The persistence-unit element defines the configuration of our persistence unit. In this example, we provide the name of the persistence unit, the transaction type, the data source, and the provider. We also specify the Hibernate dialect for MySQL, the connection details (URL, username, and password), and the hbm2ddl.auto property to update the database schema.

Using SQL Queries

Once we have configured our persistence.xml file, we can use SQL queries to interact with our MySQL database. Here's an example of how to execute a native SQL query using JPA:

@Entity
@NamedNativeQuery(
        name = "findAllUsers",
        query = "SELECT * FROM user",
        resultClass = User.class
)
public class User implements Serializable {
 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
 
    // constructors, getters and setters
 
}

In this example, we define a named native query called findAllUsers using the @NamedNativeQuery annotation. We specify the SQL query to execute and the result class to map the query results to.

We can then use this named query in our application code like this:

EntityManager em = /* obtain entity manager */;
List<User> users = em.createNamedQuery("findAllUsers", User.class).getResultList();

This will execute the SQL query and return a list of User objects.

Conclusion

Configuring the persistence.xml file for MySQL databases and using SQL queries can be a powerful combination for developing JPA/Hibernate applications. With this configuration, we can take full advantage of the power of MySQL and SQL while still using the simplicity of JPA/Hibernate.