mybatis中resultMap的association及collectio的使用详解

<!-- 一对一关联映射示例 -->
<resultMap id="UserWithDeptMap" type="com.example.User">
    <!-- 用户表字段映射 -->
    <id column="user_id" property="id" jdbcType="BIGINT"/>
    <result column="user_name" property="name" jdbcType="VARCHAR"/>
    <result column="user_age" property="age" jdbcType="INTEGER"/>

    <!-- 一对一关联 department 对象 -->
    <association property="department" javaType="com.example.Department">
        <id column="dept_id" property="id" jdbcType="BIGINT"/>
        <result column="dept_name" property="deptName" jdbcType="VARCHAR"/>
        <result column="dept_location" property="location" jdbcType="VARCHAR"/>
    </association>
</resultMap>

<select id="selectUserWithDepartment" resultMap="UserWithDeptMap">
    SELECT 
        u.id          AS user_id,
        u.name        AS user_name,
        u.age         AS user_age,
        d.id          AS dept_id,
        d.name        AS dept_name,
        d.location    AS dept_location
    FROM 
        user u
    LEFT JOIN 
        department d ON u.dept_id = d.id
    WHERE 
        u.id = #{userId}
</select>

package com.example;

public class User {
    private Long id;          // 对应 user_id 字段
    private String name;      // 对应 user_name 字段
    private Integer age;      // 对应 user_age 字段
    private Department department; // 一对一关联对象

    // 必须的 getter 和 setter 方法
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }
}

package com.example;

public class Department {
    private Long id;          // 对应 dept_id 字段
    private String deptName;  // 对应 dept_name 字段
    private String location;  // 对应 dept_location 字段

    // 必须的 getter 和 setter 方法
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }
}

<resultMap id="UserWithOrdersMap" type="com.example.model.User">
    <id property="id" column="user_id"/>
    <result property="name" column="user_name"/>
    <result property="age" column="user_age"/>
    
    <!-- 一对多关联订单集合 -->
    <collection property="orders" ofType="com.example.model.Order">
        <id property="id" column="order_id"/>
        <result property="orderNo" column="order_no"/>
        <result property="amount" column="order_amount"/>
        <result property="userId" column="user_id"/>
    </collection>
</resultMap>

<select id="selectUserWithOrders" resultMap="UserWithOrdersMap">
    SELECT 
        u.id as user_id,
        u.name as user_name,
        u.age as user_age,
        o.id as order_id,
        o.order_no as order_no,
        o.amount as order_amount,
        o.user_id
    FROM user u
    LEFT JOIN orders o ON u.id = o.user_id
    WHERE u.id = #{userId}
</select>

package com.example.model;

import java.util.List;

public class User {
    private Long id;
    private String name;
    private Integer age;
    private List<Order> orders; // 一对多关联的订单集合

    // getters and setters
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public List<Order> getOrders() {
        return orders;
    }

    public void setOrders(List<Order> orders) {
        this.orders = orders;
    }
}

package com.example.model;

public class Order {
    private Long id;
    private String orderNo;
    private Double amount;
    private Long userId; // 外键，关联用户ID

    // getters and setters
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getOrderNo() {
        return orderNo;
    }

    public void setOrderNo(String orderNo) {
        this.orderNo = orderNo;
    }

    public Double getAmount() {
        return amount;
    }

    public void setAmount(Double amount) {
        this.amount = amount;
    }

    public Long getUserId() {
        return userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }
}