# mybatis-demo

**Repository Path**: pushbug/mybatis-demo

## Basic Information

- **Project Name**: mybatis-demo
- **Description**: 关联查询Demo
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2023-10-30
- **Last Updated**: 2023-10-30

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

<h1 align="center" style="margin: 30px 0 30px; font-weight: bold;">Mybatis 关联查询</h1>
<h4 align="center">一个小Demo</h4>

## 1. 一对一
### 1.1 使用association映射
`一个丈夫对应一个妻子`
```xml
<!--association映射-->
<resultMap id="HusbandMap" type="cn.pushbug.entity.pojo.onetoone.Husband">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <association property="wife"  javaType="cn.pushbug.entity.pojo.onetoone.Wife">
        <id property="id" column="id"/>
        <result property="name" column="sid"/>
        <result property="id" column="number" />
    </association>
</resultMap>

<select id="getOne" resultMap="HusbandMap">
    select 
        *
    from husband,
        wife
    where 
        husband.id = wife.hid
        and husband.id = #{id}
</select>

```
## 2. 一对多
### 2.1 使用collection映射
`一个部门对应多个职位`
```xml
    <!--使用collection-->
    <resultMap type="cn.pushbug.entity.pojo.onetomany.Dept" id="DeptMap">
        <id property="id" column="dept_id" />
        <result property="name" column="name" jdbcType="VARCHAR"/>
        <collection property="emps" ofType="cn.pushbug.entity.pojo.onetomany.Emp">
            <result property="id" column="emp_id"/>
            <result property="deptId" column="dept_id"/>
            <result property="empName" column="emp_name"/>
        </collection>
    </resultMap>


    <select id="getMany" resultMap="DeptMap">
        SELECT dept.id AS dept_id,
               dept.name,
               emp.id AS emp_id,
               emp.dept_id,
               emp.emp_name
        FROM dept
                 JOIN emp ON dept.id = emp.dept_id
        WHERE dept.id = #{id}
    </select>
```

## 3. 多对一
### 3.1 使用association映射
`多个学生对应一个班级`
```xml
    <!--association映射-->
    <resultMap id="StudentMap" type="cn.pushbug.entity.pojo.manytoone.Student">
        <id property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="classes" javaType="cn.pushbug.entity.pojo.manytoone.Classes">
            <id property="id" column="cid"/>
            <result property="name" column="cname"/>
            <result property="sid" column="sid"/>
        </association>
    </resultMap>

    <select id="getOne" resultMap="StudentMap">
        select
            student.id as sid,
            student.name as sname,
            classes.id as cid,
            classes.name as cname
        from student,
             classes
        where student.id = classes.sid
          and student.id = #{id}

    </select>
```
## 4. 多对多
### 4.1 使用collection映射
`多个角色对应多个功能`
```xml
    <resultMap type="cn.pushbug.entity.pojo.manytomany.Role" id="RoleMap">
        <result property="id" column="id" jdbcType="INTEGER"/>
        <result property="name" column="name" jdbcType="VARCHAR"/>
        <collection property="nodes" ofType="cn.pushbug.entity.pojo.manytomany.Node">
            <id property="id" column="node_id"/>
            <result property="name" column="node_name"/>
        </collection>
    </resultMap>


    <select id="getAll" resultMap="RoleMap">
        SELECT r.id,
               r.name,
               n.id   AS node_id,
               n.name AS node_name
        FROM role r
                 LEFT JOIN role_node rn ON r.id = rn.role_id
                 LEFT JOIN node n ON rn.node_id = n.id
    </select>

```