MyBatis-Plus QueryWrapper及LambdaQueryWrapper的使用

 转载出处： https://blog.csdn.net/weixin_44684812/article/details/111151839

假如我们有一张user表，现需要通过user_name查出所有数据

@ApiModel(description = "用户实体")
public class User {

    /**
     * serialVersionUID
     */
    @ApiModelProperty(value = "主键")
    private Integer id;

    @ApiModelProperty(value = "用户名")
    private String username;

    @ApiModelProperty(value = "真实昵称")
    private String realname;

    @ApiModelProperty(value = "性别")
    private String sex;

    @ApiModelProperty(value = "工号")
    private String jobNum;

    @ApiModelProperty(value = "状态 0 启用 1 禁用")
    private Integer isDel;

    @ApiModelProperty(value = "部门")
    private Integer departmentId;

    private String departmentName;

    @ApiModelProperty(value = "密码")
    private String password;// 用户密码

    @ApiModelProperty(value = "手机")
    private String mobile;// 手机

    private Integer createUser;

    private Integer editUser;

    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    private Date gmtCreate;

    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
    private Date gmtUpdate;
    }

• QueryWrapper
  最基础的使用方式是这样

// 查询条件构造器
QueryWrapper<User > wrapper = new QueryWrapper<>();
wrapper.eq("user_name", id);
// 查询操作
List<User > users = userMapper.selectList(wrapper);

 

然后我们可以引入lambda，避免我们在代码中写类似的于user_name的硬编码

QueryWrapper wrapper = new QueryWrapper<>();
wrapper.lambda().eq(User::getuserName, userName);
List users= userMapper.selectList(wrapper);

 

• LambdaQueryWrapper
  为了简化lambda的使用，我们可以改写成LambdaQueryWrapper构造器，语法如下：

LambdaQueryWrapper<User> wrapper = new QueryWrapper<User>().lambda();
wrapper.eq(User::getuserName, userName);
List<User> users= userMapper.selectList(wrapper);

 

我们可以再次将QueryWrapper.lambda()简化，变成这个样子

LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
wrapper.eq(User::getuserName, userName);
List<User> bannerItems = userMapper.selectList(wrapper);

 

链式查询
MyBatis-Plus还提供了一种链式查询的方式，和上面的代码效果一样。
但是这种写法偏向于炫技，可读性没有上面的代码强，大家可以根据需要自行选择方式。

List<User> bannerItems = new LambdaQueryChainWrapper<>(bannerItemMapper)
                        .eq(User::getuserName, userName)
                        .list();

 

// 增加条件

int count = tcmcConfigTreeService.count(
                    new LambdaQueryWrapper<TcmcConfigTree>()
                            .eq(TcmcConfigTree::getNodeName, tcmcConfigTree.getNodeName()).ne(TcmcConfigTree::getId, tcmcConfigTree.getId())
                    
            );

LambdaQueryWrapper 条件删除

条件删除符合条件的全部删除

  LambdaQueryWrapper<USer> objectLambdaQueryChainWrapper = new LambdaQueryWrapper<>();
            objectLambdaQueryChainWrapper.eq(User::getDepartmentId, departmentId);
            cEquipmentMapper.delete(objectLambdaQueryChainWrapper);