一、接口继承

直接继承：JpaRepository<T,ID>

说明：

• T：表示实体类
• ID：对应实体类的id类型
• 功能：该接口含有多种对数据库的操作方法

package com.gg.mapper;
 
import com.gg.domain.Book;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Component;
 
/**
 * @Author: {LZG}
 * @ClassName: BookMapper
 * @Description: TODO
 * @Date: 2022/7/5 9:52
 **/
@Component
public interface BookMapper extends JpaRepository<Book,Integer> {
}

二、实现接口含有的方法

package com.gg.jpa01curd;
 
import com.gg.domain.Book;
import com.gg.mapper.BookMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.test.context.ContextConfiguration;
 
import java.util.List;
import java.util.Optional;
 
@SpringBootTest
class Jpa01CurdApplicationTests {
    @Autowired
    BookMapper bookMapper;
    //  保存
    @Test
    void contextLoads() {
//        Persistence.createEntityManagerFactory();
        List<Book> all = bookMapper.findAll();
        System.out.println(all);
    }
    @Test
    //  保存给定实体
    void test1(){
        Book book = new Book();
        book.setName("Jpa测试");
        bookMapper.save(book);
    }
 
    @Test
    //  根据id查询实体
    void test2(){
        Optional<Book> byId = bookMapper.findById(44);
        System.out.println(byId);
    }
    @Test
    //  查询所有实体
    void test3(){
        List<Book> all = bookMapper.findAll();
        System.out.println(all);
    }
 
    @Test
    //  返回实体个数
    void test4(){
        long count = bookMapper.count();
        System.out.println(count);
    }
 
    @Test
    //  删除给定实体
    void test5(){
        Book book = new Book();
        book.setName("Jpa测试");
        book.setId(44);
        bookMapper.delete(book);
    }
 
    @Test
    //  是否存在给定id实体
    void test6(){
        boolean b = bookMapper.existsById(43);
        System.out.println(b);
    }
 
    @Test
        //  分页查询
    void test7(){
        Page<Book> all = bookMapper.findAll(PageRequest.of(1, 5));
        System.out.println(all.getTotalElements());
        System.out.println(all.getTotalPages());
        System.out.println(all.getContent());
 
    }
 
 
}