Mybatis-plus之QueryWrapper、QueryChainWrapper、LambdaQueryWrapper以及LambdaQueryChainWrapper用法

前言：以前都是使用QueryWrapper的情況多一點，其余三種也沒怎么涉及。最近是因為優化一個項目，所以才突然想起。
首先准備一個對應的實體類：

@Data
@TableName("house")
public class HouseEntity {
    @TableId(type = IdType.AUTO)
    private Integer houseId;
    private String houseOwner;
    private String houseArea;
}

分別測試使用代碼測試，都以查詢所有的數據為目的。都注入

@Autowired
private HouseMapper houseMapper;

1. QueryWrapper

@Test
public void test1() {
List<HouseEntity> list=houseMapper.selectList(new QueryWrapper<HouseEntity>()
                .orderByDesc("house_area"));
        System.out.println("QueryWrapper:"+list);
    }

執行結果：QueryWrapper:[HouseEntity(houseId=2, houseOwner=LS, houseArea=72), HouseEntity(houseId=1, houseOwner=ZS, houseArea=70)]

2. QueryChainWrapper

@Test
public void test() {
List<HouseEntity> list2=new QueryChainWrapper<>(houseMapper)
                .orderByDesc("house_area").list();
        System.out.println("QueryChainWrapper:"+list);
    }

執行結果：QueryChainWrapper:[HouseEntity(houseId=2, houseOwner=LS, houseArea=72), HouseEntity(houseId=1, houseOwner=ZS, houseArea=70)]

3. LambdaQueryWrapper

@Test
public void test3() {
List<HouseEntity> list=houseMapper.selectList(new LambdaQueryWrapper<HouseEntity>()
                .orderByDesc(HouseEntity::getHouseArea));
       System.out.println("LambdaQueryWrapper:"+list);
    }

執行結果：LambdaQueryWrapper:[HouseEntity(houseId=2, houseOwner=LS, houseArea=72), HouseEntity(houseId=1, houseOwner=ZS, houseArea=70)]

4. LambdaQueryChainWrapper

@Test
public void test3() {
List<HouseEntity> list = new LambdaQueryChainWrapper<>(houseMapper)
                .orderByDesc(HouseEntity::getHouseArea).list();
        System.out.println("LambdaQueryChainWrapper:"+list);
  }
執行結果：LambdaQueryChainWrapper:[HouseEntity(houseId=2, houseOwner=LS, houseArea=72), HouseEntity(houseId=1, houseOwner=ZS, houseArea=70)]

總結：

1. QueryWrapper、QueryChainWrapper只能都只能指定需要的數據庫列名
2. LambdaQueryWrapper、LambdaQueryChainWrapper可以通過獲取Lambda數據庫列名
3. QueryWrapper 、LambdaQueryWrapper不能使用鏈式查詢的方式，必須借助BaseMapper來執行
4. QueryChainWrapper、LambdaQueryChainWrapper可以使用鏈式查詢的方式，如list(),one()