How to use springboot+mybatis plus to implement tree structure query

Background

In the actual development process, it is often necessary to query the node tree and obtain the child node list based on the specified node. The operation of obtaining the node tree is recorded below, in case of emergency.

Usage scenarios

Can be used for data structures with hierarchical relationships such as system department organizations, product classifications, city relationships, etc.;

Design ideas

Recursive model

That is, root node, branch node, leaf node, the data model is as follows:

##110000PC0220000手机0310001Lenovo Notebook10000410002HP Notebook1000056Implementation code

id	code	name	parent_code
##1000101	Lenovo Savior	10001
1000102	Lenovo Xiaoxin Series	10001

Table structure

CREATE TABLE `tree_table` (
  `id` int NOT NULL AUTO_INCREMENT COMMENT "主键ID",
  `code` varchar(10) NOT NULL COMMENT "编码",
  `name` varchar(20) NOT NULL COMMENT "名称",
  `parent_code` varchar(10)  NOT NULL COMMENT "父级编码",
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC COMMENT="树形结构测试表";

Table data

INSERT INTO `tree_table`(`code`, `name`, `parent_code`) VALUES ("10000", "电脑", "0");
INSERT INTO `tree_table`(`code`, `name`, `parent_code`) VALUES ("10001", "联想笔记本", "10000");
INSERT INTO `tree_table`(`code`, `name`, `parent_code`) VALUES ("10002", "惠普笔记本", "10000");
INSERT INTO `tree_table`(`code`, `name`, `parent_code`) VALUES ("1000101", "联想拯救者", "10001");
INSERT INTO `tree_table`(`code`, `name`, `parent_code`) VALUES ("1000102", "联想小新系列", "10001");

Entity

@Data
@TableName("tree_table")
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
public class TreeTable {

    /**
     * 主键ID
     */
    @TableId(type = IdType.AUTO)
    private Integer id;
    /**
     * 编码
     */
    private String code;
    /**
     * 名称
     */
    private String name;
    /**
     * 父级编码
     */
    private String parentCode;

    /**
     * 子节点
     */
    @TableField(exist = false)
    private List<TreeTable> childNode;
}

mybatis

mapper

public interface TreeTableMapper extends BaseMapper<TreeTable> {
    /**
     * 获取树形结构数据
     *
     * @return 树形结构
     */
    public List<TreeTable> noteTree();
}

xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.springboot.example.mysqltree.mapper.TreeTableMapper">
    <resultMap id="BaseResultMap" type="com.springboot.example.mysqltree.model.entity.TreeTable">
        <result column="id" property="id"/>
        <result column="code" property="code"/>
        <result column="name" property="name"/>
        <result column="parent_code" property="parentCode"/>
    </resultMap>
    <resultMap id="NodeTreeResult" type="com.springboot.example.mysqltree.model.entity.TreeTable"
               extends="BaseResultMap">
        <collection property="childNode" column="code" ofType="com.springboot.example.mysqltree.model.entity.TreeTable"
                    javaType="java.util.ArrayList" select="nextNoteTree">

        </collection>
    </resultMap>

    <sql id="Base_Column_List">
                id,
                code,
                `name`,
                parent_code
    </sql>
   
    <select id="nextNoteTree" resultMap="NodeTreeResult">
        select
        <include refid="Base_Column_List"/>
        from tree_table
        where parent_code=#[code]
    </select>
    <select id="noteTree" resultMap="NodeTreeResult">
        select
        <include refid="Base_Column_List"/>
        from tree_table
        where parent_code="0"
    </select>
</mapper>

noteTree: Get all parent node data;
nextNoteTree: loop to obtain child node data until the end of the leaf node;
column: the column name of the associated table;
ofType: Return type
Startup class

@Slf4j
@Component
public class TreeTableCommandLineRunner implements CommandLineRunner {
    @Resource
    private TreeTableMapper treeTableMapper;

    @Override
    public void run(String... args) throws Exception {
        log.info(JSONUtil.toJsonPrettyStr(treeTableMapper.noteTree()));
    }
}

Final effect

[
    {
        "code": "10000",
        "childNode": [
            {
                "code": "10001",
                "childNode": [
                    {
                        "code": "1000101",
                        "childNode": [
                        ],
                        "parentCode": "10001",
                        "name": "联想拯救者",
                        "id": 5
                    },
                    {
                        "code": "1000102",
                        "childNode": [
                        ],
                        "parentCode": "10001",
                        "name": "联想小新系列",
                        "id": 6
                    }
                ],
                "parentCode": "10000",
                "name": "联想笔记本",
                "id": 3
            },
            {
                "code": "10002",
                "childNode": [
                ],
                "parentCode": "10000",
                "name": "惠普笔记本",
                "id": 4
            }
        ],
        "parentCode": "0",
        "name": "电脑",
        "id": 1
    }
]

Notes

If the mapper xml cannot be loaded when using mybatis, you need to add the following configuration to pom.xml:

<resources>
    <resource>
        <directory>src/main/resources</directory>
        <filtering>true</filtering>
    </resource>
    <resource>
        <directory>src/main/java</directory>
        <includes>
            <include>**/*.xml</include>
        </includes>
    </resource>
</resources>

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