MyBatis-plus中的 @TableField(exist = false)注解

应用场景：

当往实体类加入新属性，希望basemapper的基础查询可以忽略该属性

例子：

有实体类Permission

public class Permission implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId(value = "permission_id", type = IdType.ID_WORKER_STR)
    private String permissionId;
    private String permissionUrl;
    private String permissionCode;
    private String permissionDesc;
    private String permissionStatus;
    private String parentId;
}

一一映射数据库中的字段

当往实体类中添加数据库中没有的属性时

public class Permission implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId(value = "permission_id", type = IdType.ID_WORKER_STR)
    private String permissionId;
    private String permissionUrl;
    private String permissionCode;
    private String permissionDesc;
    private String permissionStatus;
    private String parentId;

    //额外添加的两个字段
    private List<Permission> children;
    private Integer level;
}

使用basemapper查询

List<Permission> permissionList = baseMapper.selectList(wrapper);

报错,因为数据库中没有多出来的这两个字段，sql语句语句中可以看到多出来了children，与level字段，由于数据库中没有这两个字段，所以报错。

Error querying database.  Cause: java.sql.SQLSyntaxErrorException: Unknown column 'children' in 'field list'
The error may exist in xyz/lande/demo/mapper/PermissionMapper.java (best guess)
The error may involve defaultParameterMap
The error occurred while setting parameters
SQL: SELECT  permission_id,permission_url,permission_code,permission_desc,permission_status,parent_id,children,level  FROM permission  WHERE  1=1 ORDER BY permission_id DESC
Cause: java.sql.SQLSyntaxErrorException: Unknown column 'children' in 'field list'
; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: Unknown column 'children' in 'field list'] with root cause

现在加上注解 @TableField(exist = false)

public class Permission implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId(value = "permission_id", type = IdType.ID_WORKER_STR)
    private String permissionId;
    private String permissionUrl;
    private String permissionCode;
    private String permissionDesc;
    private String permissionStatus;
    private String parentId;

    //额外添加的两个字段
    @TableField(exist = false)
    private List<Permission> children;
    @TableField(exist = false)
    private Integer level;
}

运行后再次测试

 Preparing: SELECT permission_id,permission_url,permission_code,permission_desc,permission_status,parent_id FROM permission WHERE 1=1 ORDER BY permission_id DESC

发现sql语句中语句去除了这两个字段。