Java Persistence API (JPA) is a Java specification for accessing, persisting, and managing data between Java objects and relational databases. It provides a standard set of annotations and interfaces for mapping Java classes to database tables, defining relationships between tables, and performing CRUD (Create, Read, Update, Delete) operations.
JPA is a part of the Java Enterprise Edition (JavaEE) platform and it is based on the Java Persistence Object-Relational Mapping (ORM) framework. It provides a common way to access relational databases in Java, regardless of the underlying database management system (DBMS).
Getting Started with JPA
To use JPA, you need to have a basic understanding of databases and SQL. Then, you need to include the JPA implementation library, such as Hibernate or EclipseLink, in your project classpath.
Here's a simple example to illustrate how to use JPA in Java:
In the above example, we define a User class that represents a row in the users table. The @Entity annotation tells JPA that this class is an entity and should be persisted to a database. The @Table annotation specifies the name of the table in the database.
The id field is annotated with @Id to indicate that it is the primary key for the table. The @GeneratedValue annotation specifies that the value of the id field should be generated by the database when a new row is inserted.
The name and age fields are annotated with @Column to specify the names of the corresponding columns in the users table.
With the entity class defined, we can use JPA to perform CRUD operations on the users table. For example, to insert a new row into the users table, we can use the following code:
In this example, we create a new User object and set its name and age fields. Then, we obtain an EntityManager object, which is the main interface for interacting with the JPA persistence context.
Next, we begin a transaction and call the persist method on the EntityManager to persist the User object to the database. Finally, we commit the transaction to save the changes to the database.
JPA Queries
JPA provides several ways to query the database, including:
JPQL (Java Persistence Query Language): A high-level, object-oriented query language that is similar to SQL.
Criteria API: A programmatic, type-safe API for building and executing queries.
Native SQL: A low-level, SQL-based API for
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