Spring - JPA

Spring Data JPA focuses on using JPA to store data in a relational database. Its most compelling feature is the ability to create repository implementations automatically, at runtime, from a repository interface.

Spring Data JPA is a library / framework that adds an extra layer of abstraction on the top of our JPA provider.

Dependencies

• JDBC Driver
• Datasource (MySQL)
• JPA Provider (Hibernate)

Why use Spring Data JPA

它的核心价值是减少样板代码。很多常见的增删改查不需要手写大量 DAO 实现，只需要定义实体和 Repository 接口，就可以先把数据访问层搭起来。

Configuration

applicationContext.xml

Github spring-data-jpa-examples

• DataSource
• entityManagerFactory
• transactionManager
• hibernateProperties

CRUD Example

Create an interface that extends the CrudRepository interface

import org.springframework.data.repository.CrudRepository;
interface TodoRepository extends CrudRepository<TypeOfEntity, TypeOfEntityId> {
}

Create Query from Method Name

import org.springframework.data.jpa.repository.JpaRepository;

public interface PersonRepository extends JpaRepository<Person, Long> {

    /**
     * Finds persons by using the last name as a search criteria.
     * @param lastName
     * @return  A list of persons which last name is an exact match with the given last name.
     *          If no persons is found, this method returns an empty list.
     */
    public List<Person> findByLastName(String lastName);
}

Using Created Query Methods

@Service
public class someServices() {
     @Resource
     private PersonRepository personRepository;
     public List<Person> search(String searchTerm) {
        return personRepository.findAll(lastNameIsLike(searchTerm));
    }
}

Spring Data JPA, Hibernate

Spring Data JPA 通常运行在 Hibernate 这样的 JPA Provider 之上。可以把它理解成：

• JPA：一套规范
• Hibernate：常见实现
• Spring Data JPA：在实现之上再封装一层更方便的 Repository 模型

参考：https://baijiahao.baidu.com/s?id=1661937038552348304&wfr=spider&for=pc

Links

• Spring Data JPA Tutorial
• Spring Data JPA Reference
• Spring JPA Data + Hibernate + MySQL + Maven