mybatis-plus多表联查join的实现
spring-java 人气:01、安装依赖
<dependency> <groupId>com.github.yulichang</groupId> <artifactId>mybatis-plus-join</artifactId> <version>1.2.4</version> </dependency>
2、定义三个基本实体类
2.1 User类
@Data public class User { //对应数据库的主键(uuid,自增id,雪花算法,redis,zookper) @TableId(type = IdType.AUTO) private Integer id; @NotNull(message = "名称xxx不能为空")//空校验 @NotBlank //不能为空字符串 @Size(min = 1,max = 5,message = "ssssss")//字符串长度校验 private String name; // @Min(value = 10,message = "最小值10") // @Max(value = 90,message = "最大值为99") @NotNull // @Max(value = 50,message = "超过最大值") // @Min(value = 10,message = "超过最小值") @Range(min=10,max = 99,message = "错误")//数字范围校验 private Integer age; @NotNull private String email; //逻辑删除字段 @TableLogic //逻辑删除注解 private Integer deleted; //字段添加填充内容 //策略 // @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss") @TableField(fill = FieldFill.INSERT) @DateTimeFormat(pattern = "yyyy-MM-dd") @JsonFormat(pattern = "yyyy-MM-dd", timezone = "GMT+8") private LocalDateTime createTime; //策略 // @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss") @JsonFormat(pattern = "yyyy-MM-dd", timezone = "GMT+8") @TableField(fill = FieldFill.INSERT_UPDATE) private LocalDateTime updateTime; @TableField(fill = FieldFill.INSERT) private Integer createBy; @TableField(fill = FieldFill.INSERT_UPDATE) private Integer updateBy; @Version//乐观锁注解 private Integer version; }
2.2 UserScore类
@Data public class UserScore { @TableId(type = IdType.AUTO) private long id; private String course; private String score; private Long userId; }
2.3 UserCourseTeacher类
@Data public class UserCourseTeacher { @TableId(type = IdType.AUTO) private Integer id; private Long teacher; private Long userCourseId; }
3、定义三个mapper
3.1 userMapper
@Repository @Mapper public interface UserMapper extends MPJBaseMapper<User> { }
3.2 UserScoreMapper
@Repository @Mapper public interface UserScoreMapper extends MPJBaseMapper<UserScore> { }
3.3 UserCourseTeacherMapper
@Mapper @Repository public interface UserCourseTeacherMapper extends MPJBaseMapper<UserCourseTeacher> { }
4、定义返回值dto
@Data public class UserTeacherDto extends User { private String course; private String score; private String teacher; }
5、开发业务层
例如对应的sql为
select a.*,b.score,b.course,c.teacher from user a left join user_score b on a.id=b.user_id left join user_course_teacher c on b.id=c.user_course_id
则代码为
public List<UserTeacherDto> GetAllUserTeacher(){ MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>() .selectAll(User.class) .select(UserScore::getScore,UserScore::getCourse) .select(UserCourseTeacher::getTeacher) .leftJoin(UserScore.class,UserScore::getUserId,User::getId) .leftJoin(UserCourseTeacher.class,UserCourseTeacher::getUserCourseId,UserScore::getId); List<UserTeacherDto> list=userMapper.selectJoinList(UserTeacherDto.class, mPJLambdaWrapper); return list; }
6、假如进行分页查询的话
@Override public Map<String,Object> GetUserDtoByPage(){ Map<String,Object> result=new HashMap<>(); MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>() .selectAll(User.class) .select(UserScore::getScore,UserScore::getCourse) .leftJoin(UserScore.class,UserScore::getUserId,User::getId); IPage<UserDto> UserDtoPage=userMapper.selectJoinPage( new Page<UserDto>(3,2), UserDto.class, mPJLambdaWrapper ); result.put("list",UserDtoPage.getRecords()); result.put("count",UserDtoPage.getTotal()); return result; }
7、注意:
- selectAll():查询指定实体类的全部字段
- select():查询指定的字段,支持可变长参数同时查询多个字段,但是在同一个select中只能查询相同表的字段,所以如果查询多张表的字段需要分开写
- selectAs():字段别名查询,用于数据库字段与接收结果的dto中属性名称不一致时转换
- leftJoin():左连接,其中第一个参数是参与联表的表对应的实体类,第二个参数是这张表联表的ON字段,第三个参数是参与联表的ON的另一个实体类属性
8、其他
MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>() .selectAll(User.class)
中的User可以理解为主表
leftJoin函数参数顺序依次为:子表的类型、子表的字段(实体类属性)、主表实体类的属性,就是用于on关联的
9、如果针对条件进行动态查询
@Override public List<UserTeacherDto> GetAllUserTeacher(Map<String,Long> params){ System.out.println("传递参数"); System.out.println(params.get("id")); MPJLambdaWrapper<User> mPJLambdaWrapper=new MPJLambdaWrapper<User>() .selectAll(User.class) .select(UserScore::getScore,UserScore::getCourse) .select(UserCourseTeacher::getTeacher) .leftJoin(UserScore.class,UserScore::getUserId,User::getId) .leftJoin(UserCourseTeacher.class,UserCourseTeacher::getUserCourseId,UserScore::getId); if(params.get("id")!=null && params.get("id").toString()!=""){ mPJLambdaWrapper.eq(UserScore::getId,params.get("id")); } List<UserTeacherDto> list=userMapper.selectJoinList(UserTeacherDto.class, mPJLambdaWrapper); return list; }
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