树形表，自关联表查询技巧

news2025/7/10 3:56:06

方法一：部门表，部门表中除了自身主键id外，还有另一个字段parentId父id，可以一直递归下去

数据库表：

菜单这样展示就需要我们在接口的返回值中，返回这样的层级数据：

[
  {
    "id": 1,
    "name": "股东会",
    "parentId": -1,
    "depPath": ".1",
    "enabled": true,
    "isParent": true,
    "children": [
      {
        "id": 2,
        "name": "董事会",
        "parentId": 1,
        "depPath": ".1.2",
        "enabled": true,
        "isParent": true,
        "children": [
          {
            "id": 3,
            "name": "总办",
            "parentId": 2,
            "depPath": ".1.2.3",
            "enabled": true,
            "isParent": true,
            "children": [
              {
                "id": 4,
                "name": "财务部",
                "parentId": 3,
                "depPath": ".1.2.3.4",
                "enabled": true,
                "isParent": false,
                "children": [],
                "result": null
              },
              {
                "id": 5,
                "name": "市场部",
                "parentId": 3,
                "depPath": ".1.2.3.5",
                "enabled": true,
                "isParent": true,
                "children": [
                  {
                    "id": 6,
                    "name": "华东市场部",
                    "parentId": 5,
                    "depPath": "1.2.3.5.6",
                    "enabled": true,
                    "isParent": true,
                    "children": [
                      {
                        "id": 8,
                        "name": "上海市场部",
                        "parentId": 6,
                        "depPath": "1.2.3.5.6.8",
                        "enabled": true,
                        "isParent": false,
                        "children": [],
                        "result": null
                      }
                    ],
                    "result": null
                  },
                  {
                    "id": 7,
                    "name": "华南市场部",
                    "parentId": 5,
                    "depPath": "1.2.3.5.7",
                    "enabled": true,
                    "isParent": false,
                    "children": [],
                    "result": null
                  },
                  {
                    "id": 9,
                    "name": "西北市场部",
                    "parentId": 5,
                    "depPath": ".1.2.3.5.9",
                    "enabled": true,
                    "isParent": true,
                    "children": [
                      {
                        "id": 10,
                        "name": "贵阳市场",
                        "parentId": 9,
                        "depPath": ".1.2.3.5.9.10",
                        "enabled": true,
                        "isParent": true,
                        "children": [
                          {
                            "id": 11,
                            "name": "乌当区市场",
                            "parentId": 10,
                            "depPath": ".1.2.3.5.9.10.11",
                            "enabled": true,
                            "isParent": false,
                            "children": [],
                            "result": null
                          }
                        ],
                        "result": null
                      }
                    ],
                    "result": null
                  }
                ],
                "result": null
              },
              {
                "id": 12,
                "name": "技术部",
                "parentId": 3,
                "depPath": ".1.2.3.12",
                "enabled": true,
                "isParent": false,
                "children": [],
                "result": null
              },
              {
                "id": 13,
                "name": "运维部",
                "parentId": 3,
                "depPath": ".1.2.3.13",
                "enabled": true,
                "isParent": true,
                "children": [
                  {
                    "id": 149,
                    "name": "测试部门1",
                    "parentId": 13,
                    "depPath": ".1.2.3.13.149",
                    "enabled": true,
                    "isParent": false,
                    "children": [],
                    "result": null
                  }
                ],
                "result": null
              }
            ],
            "result": null
          }
        ],
        "result": null
      }
    ],
    "result": null
  }
]

返回这样的数据：其中有个简单的方法

1：修改数据库表对应的实体类，给实体类添加一个字段 children

@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@TableName("t_department")
@ApiModel(value="Department对象", description="")
public class Department implements Serializable {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "id")
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;

    @ApiModelProperty(value = "部门名称")
    private String name;

    @ApiModelProperty(value = "父id")
    private Integer parentId;

    @ApiModelProperty(value = "路径")
    private String depPath;

    @ApiModelProperty(value = "是否启用")
    private Boolean enabled;

    @ApiModelProperty(value = "是否上级")
    private Boolean isParent;

    @ApiModelProperty(value = "子部门列表")
    @TableField(exist = false)
    private List<Department> children;

    @ApiModelProperty(value = "返回结果，存储过程使用")
    @TableField(exist = false)
    private Integer result;

}

2. 正常的写Controlelr，service，下面给出ServiceImpl后面的代码

ServiceImpl.java

这里-1是顶级节点的parentId为-1

    /**
     * 获取所有部门
     * @return
     */
    @Override
    public List<Department> getAllDepartments() {
        return departmentMapper.getAllDepartments(-1);
    }

Mapper.java

    /**
     * 获取所有部门
     * @return
     */
    List<Department> getAllDepartments(Integer parentId);

Mapper.xml

定义一个返回的Map，在这个Map中，通过collection标签的 select 属性，来给这个集合赋值，每次赋值就再调用一下 getAllDepartments方法查询一次，携带的参数为第一次查询时候的主键id

    <!--获取所有部门-->
    <select id="getAllDepartments" resultMap="DepartmentWithChildren" parameterType="Integer">
        select
        <include refid="Base_Column_List" />
        from t_department
        where parentId = #{parentId}
    </select>


     <resultMap id="DepartmentWithChildren" type="com.example.pojo.Department" extends="BaseResultMap">
        <!--select 相当是拿到children，如何拿到值呢，那就再调用一下这个方法，传id-->
        <collection property="children" ofType="com.example.pojo.Department" select="com.example.mapper.DepartmentMapper.getAllDepartments" column="id">
        </collection>
    </resultMap>

    <!-- 通用查询结果列 -->
    <sql id="Base_Column_List">
        id, name, parentId, depPath, enabled, isParent
    </sql>