Spring Data Jpa

Table of Contents

• Introduction
• Spring Data JPA
• JPA
• Hibernate Lifecycle
• Project DataBase Class Diagram
• Setup and Installation

Introduction

Comprehensive Guide to Spring Data JPA, JPA, and Hibernate.

Spring Data JPA

Spring Data JPA is part of the Spring Data family and provides a repository-based abstraction for data access. It makes it easy to implement JPA-based repositories with minimal code.

Key Features of Spring Data JPA

1. Repositories

   • Interface-based repository support with CRUD operations.
   • CrudRepository, JpaRepository, PagingAndSortingRepository.

2. Query Methods

   • Method naming conventions for query creation.
   • findBy, findAll, countBy, etc.

3. Custom Queries

   • Support for JPQL, native SQL, and query derivation from method names.

Example Repository

public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByLastName(String lastName);
}

JPA

Java Persistence API (JPA) is a specification for accessing, persisting, and managing data between Java objects/classes and a relational database. JPA is a standard specification, and it requires an implementation to work, such as Hibernate, EclipseLink, or OpenJPA.

JPA Annotations

• @Entity: Specifies that the class is an entity.
• @Table: Specifies the table in the database.
• @Id: Specifies the primary key.
• @GeneratedValue: Specifies the generation strategy for the primary key.
• @Column: Specifies the column in the table.

Hibernate Lifecycle

Hibernate is an ORM (Object-Relational Mapping) tool that simplifies the interaction between Java applications and relational databases. Understanding the Hibernate lifecycle is crucial for effectively using Hibernate in your project.

Hibernate Lifecycle States

1. Transient State

   • An object is in a transient state when it is instantiated using the new operator and is not associated with a Hibernate session.
   • It is not saved in the database and does not have a database identifier.

2. Persistent State

   • An object enters the persistent state when it is associated with a Hibernate session.
   • It is saved in the database, and any changes made to the object are synchronized with the database.
   • It can be achieved using methods like session.save(), session.persist(), or session.update().

3. Detached State

   • An object is in a detached state when the Hibernate session is closed, and the object is no longer associated with any session.
   • Changes made to a detached object are not automatically synchronized with the database.
   • You can reattach a detached object to a session using methods like session.merge() or session.update().

4. Removed State

   • An object is in the removed state when it is marked for deletion but the deletion is not yet reflected in the database.
   • This can be done using the session.delete() method.

Project DataBase Class Diagram

Setup and Installation

Provide instructions on how to set up and install your project. This can include:

• Prerequisites (e.g., JDK, Maven/Gradle)
• Cloning the repository
• Setting up the database
• Running the application.