MybatisPlus:中QueryWrapper＜＞().lambda使用(条件查询)

Posted 2021-08-17 最小的帆也能远航

MyBatis-Plus QueryWrapper及LambdaQueryWrapper的使用
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
// 查询操作
List<User > users = userMapper.selectList(new QueryWrapper<User>()
                                            .eq("user_name", id));

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

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

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

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