MyBatis-Plus联表查询(Mybatis-Plus-Join)

1. 简介

   支持连表查询的mybatis-plus,mybatis-plus风格的连表操作提供 wrapper.leftJoin() wrapper.rightJoin()等操作

2. pom.xml

   
       com.github.yulichang
       mybatis-plus-join-boot-starter
       1.4.4
   
   
   注意: mybatis plus version >= 3.3.0

3. 代码生成(MybatisX)

   参考：https://blog.csdn.net/tongxin_tongmeng/article/details/128627980

4. 引入方式

   1.将代码生成的mapper改为继承MPJBaseMapper (必选)
   
   2.将代码生成的service继承MPJBaseService (可选)
   
   3.将代码生成的serviceImpl继承MPJBaseServiceImpl (可选)
   
   注意：需要连接的表都进行代码生成和上述继承类变更。

5. 项目实战

   1.原始SQL
   SELECT
      bbb.symbol_id,
      aaa.intepn,
      aaa.componen_id,
      ccc.supppn,
      ddd.symbolinctimestamp
   FROM
      librarygraphic bbb
      LEFT JOIN componen aaa ON bbb.componen_id = aaa.componen_id
      LEFT JOIN supppart ccc ON aaa.componen_id = ccc.componen_id
      LEFT JOIN logicsymbol ddd ON bbb.symbol_id = ddd.symbol_id
   WHERE
      bbb.symbol_id IS NOT NULL
      AND aaa.intepn IS NOT NULL
      AND ddd.symbolinctimestamp IS NOT NULL
      AND aaa.grpname='Connector'
      AND aaa.latest = 1
   
   2.视图实体(封装查询结果)
   @Data
   public class LibrarygraphicBo {
   
       private String symbolId;
   
       private String intepn;
   
       private String componenId;
   
       private String supppn;
   
       private String symbolinctimestamp;
   
   }
   
   3.Mybatis-Plus-Join
   MPJLambdaWrapper wrapper = new MPJLambdaWrapper()
           .selectAs(Librarygraphic::getSymbolId, LibrarygraphicBo::getSymbolId)
           .selectAs(Componen::getIntepn, LibrarygraphicBo::getIntepn)
           .selectAs(Componen::getComponenId, LibrarygraphicBo::getComponenId)
           .selectAs(Supppart::getSupppn, LibrarygraphicBo::getSupppn)
           .selectAs(Logicsymbol::getSymbolinctimestamp, LibrarygraphicBo::getSymbolinctimestamp)
           .leftJoin(Componen.class, Componen::getComponenId, Librarygraphic::getComponenId)
           .leftJoin(Supppart.class, Supppart::getComponenId, Componen::getComponenId)
           .leftJoin(Logicsymbol.class, Logicsymbol::getSymbolId, Librarygraphic::getSymbolId)
           .isNotNull(Librarygraphic::getSymbolId)
           .isNotNull(Componen::getIntepn)
           .isNotNull(Logicsymbol::getSymbolinctimestamp)
           .eq(Componen::getGrpname, "Connector")
           .eq(Componen::getLatest, 1);
   
   List boList = librarygraphicMapper.selectJoinList(LibrarygraphicBo.class, wrapper);
   
   注意：最终查询结果封装到了LibrarygraphicBo类型的集合

6. 在线文档

   https://gitee.com/best_handsome/mybatis-plus-join