<!--mybatis-plus起步依賴-->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.3.1</version>
</dependency>

public interface 原來的Mapper extends BaseMapper<這里填入這個mapper對應(yīng)的實體類> {

}

@TableName("這里填寫表名") // 指定數(shù)據(jù)庫表的對應(yīng)

@TableId(value = "這里填寫主鍵字段名",type = IdType.AUTO) // 指定主鍵的對應(yīng)

@TableField("這里填寫字段名") // 指定字段的對應(yīng)

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@TableName("table_name")
public class tableName implements Serializable {
    @TableId(value = "table_id",type = IdType.AUTO)
    private Long tableId;
    @TableField("table_field")
    private String tableField;
}

List<xx> xxList = xxMapper.selectList(new QueryWrapper<xx>());

UPDATE user SET balance = balance - 200 WHERE id in (1, 2, 4)

@Test
void testUpdateWrapper() {
    List<Long> ids = List.of(1L, 2L, 4L);
    // 1.生成SQL
    UpdateWrapper<User> wrapper = new UpdateWrapper<User>()
            .setSql("balance = balance - 200") // SET balance = balance - 200
            .in("id", ids); // WHERE id in (1, 2, 4)
        // 2.更新，注意第一個參數(shù)可以給null，也就是不填更新字段和數(shù)據(jù)，
    // 而是基于UpdateWrapper中的setSQL來更新
    userMapper.update(null, wrapper);
}

@Test
void testLambdaQueryWrapper() {
    // 1.構(gòu)建條件 WHERE username LIKE "%o%" AND balance >= 1000
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.lambda()
            .select(User::getId, User::getUsername, User::getInfo, User::getBalance)
            .like(User::getUsername, "o")
            .ge(User::getBalance, 1000);
    // 2.查詢
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

@Test
void testCustomWrapper() {
    // 1.準(zhǔn)備自定義查詢條件
    List<Long> ids = List.of(1L, 2L, 4L);
    QueryWrapper<User> wrapper = new QueryWrapper<User>().in("id", ids);
?
    // 2.調(diào)用mapper的自定義方法，直接傳遞Wrapper
    userMapper.deductBalanceByIds(200, wrapper);
}

package com.itheima.mp.mapper;
?
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.itheima.mp.domain.po.User;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Update;
import org.apache.ibatis.annotations.Param;
?
public interface UserMapper extends BaseMapper<User> {
    @Select("UPDATE user SET balance = balance - #{money} ${ew.customSqlSegment}")
    void deductBalanceByIds(@Param("money") int money, @Param("ew") QueryWrapper<User> wrapper);
}

<select id="queryUserByIdAndAddr" resultType="com.itheima.mp.domain.po.User">
      SELECT *
      FROM user u
      INNER JOIN address a ON u.id = a.user_id
      WHERE u.id
      <foreach collection="ids" separator="," item="id" open="IN (" close=")">
          #{id}
      </foreach>
      AND a.city = #{city}
  </select>

@Test
void testCustomJoinWrapper() {
    // 1.準(zhǔn)備自定義查詢條件
    QueryWrapper<User> wrapper = new QueryWrapper<User>()
            .in("u.id", List.of(1L, 2L, 4L))
            .eq("a.city", "北京");
?
    // 2.調(diào)用mapper的自定義方法
    List<User> users = userMapper.queryUserByWrapper(wrapper);
?
    users.forEach(System.out::println);
}

@Select("SELECT u.* FROM user u INNER JOIN address a ON u.id = a.user_id ${ew.customSqlSegment}")
List<User> queryUserByWrapper(@Param("ew")QueryWrapper<User> wrapper);

<select id="queryUserByIdAndAddr" resultType="com.itheima.mp.domain.po.User">
    SELECT * FROM user u INNER JOIN address a ON u.id = a.user_id ${ew.customSqlSegment}
</select>

public interface xxService extends IService<你的pojo> {
}

@Service
public class xxServiceImpl extends ServiceImpl<你的Mapper, 你的pojo> implements xxService {
}