JPA 基础(一)

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一、什么是JPA

JPA全称Java Persistence API，是一组用于将数据存入数据库的类和方法的集合。

二、JPA的基本配置

1 jpa配置

<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

2 创建dto对象

package com.example.demo.dto;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Customer {
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;
    private String firstName;
    private String lastName;
    protected Customer() {}
    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
    @Override
    public String toString() {
        return String.format(
                "Customer[id=%d, firstName='%s', lastName='%s']",
                id, firstName, lastName);
    }
}

3 创建操作数据的Repository对象

package com.example.demo.repositories;
import com.example.demo.dto.Customer;
import org.springframework.data.jpa.repository.JpaRepository;
public interface CustomerRepository extends JpaRepository<Customer, Long>; {
}

三、JpaRepository

JpaRepository

PagingAndSortingRepository

CrudRepository

QueryByExampleExecutor

四、自定义的方法

1.一些基本的自定义方法样例

2.举个例子

在CustomerRepository接口中，有如下定义

/**
 * 根据lastName查询结果
 * @param lastName
 * @return
 */
List<Customer> findByLastName(String lastName);