mybatis一对多实现延迟加载

mybatis一对多实现延迟加载

需求：一个用户可以有多个账户，查询用户时实现账户的延迟加载

1、用户实体类

package com.yl.bean;

import java.io.Serializable;
import java.sql.Date;
import java.util.List;

/**
 * 用户实体类
 */
public class User implements Serializable {
    private Integer id;//id
    private String username;//用户名
    private Date birthday;//生日
    private String sex;//性别
    private String address;//地址
    private List<Account> accountList;//用户所拥有的账户

    public User() {
    }

    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public List<Account> getAccountList() {
        return accountList;
    }

    public void setAccountList(List<Account> accountList) {
        this.accountList = accountList;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

2、账户实体类

package com.yl.bean;

import java.io.Serializable;

/**
 * 账户实体类
 */
public class Account implements Serializable {
    private Integer id;//账户id
    private Integer uid;//用户id
    private Double money;//余额
    private User user;//账户所属用户

    public Account() {
    }

    public Integer getId() {
        return id;
    }

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

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public Double getMoney() {
        return money;
    }

    public void setMoney(Double money) {
        this.money = money;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

3、用户持久层接口

package com.yl.dao;

import com.yl.bean.User;

import java.util.List;

/**
 * 用户持久层接口
 */
public interface IUserDao {

    /**
     * 查询所有用户
     */
    List<User> queryAll();

    /**
     * 根据id查询用户
     */
    User queryById(int id);

}

4、账户持久层接口

package com.yl.dao;

import com.yl.bean.Account;
import com.yl.bean.User;

import java.util.List;

/**
 * 账户持久层接口
 */
public interface IAccountDao {

    /**
     * 查询所有账户
     */
    List<Account> queryAll();

    /**
     * 根据用户id查询账户
     */
    List<Account> queryByUid(int uid);
}

5、全局配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <settings>
        <!--开启延迟加载-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

    <!--配置别名-->
    <typeAliases>
        <package name="com.yl.bean"/>
    </typeAliases>

    <!--配置mybatis环境-->
    <environments default="mysql">
        <!--配置mysql环境-->
        <environment id="mysql">
            <!--事务类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--数据源-->
            <dataSource type="POOLED">
               <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?characterEncoding=utf8&amp;serverTimezone=GMT%2B8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <!--指定映射配置文件位置-->
    <mappers>
        <mapper resource="IUserDao.xml"></mapper>
        <mapper resource="IAccountDao.xml"></mapper>
    </mappers>
</configuration>

6、用户映射配置文件

<?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.yl.dao.IUserDao">
    <!--配置用户实体类和数据库的对应信息-->
    <resultMap id="userMap" type="com.yl.bean.User">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="birthday" column="birthday"></result>
        <result property="sex" column="sex"></result>
        <result property="address" column="address"></result>
        <!--根据id查询账户-->
        <collection property="accountList" ofType="com.yl.bean.Account" select="com.yl.dao.IAccountDao.queryByUid" column="id"></collection>
    </resultMap>

    <!--查询所有用户-->
    <select id="queryAll" resultMap="userMap">
        SELECT * FROM USER
    </select>
    <!--根据id查询用户-->
    <select id="queryById" resultType="user" parameterType="int">
        select * from user where id=#{id}
    </select>
</mapper>

7、账户映射配置文件

<?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.yl.dao.IAccountDao">
    <!--配置Account属性对应数据库信息-->
    <resultMap id="accountUserMap" type="account">
        <id property="id" column="id"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
        <!--通过id查询用户-->
        <association property="user" column="uid" javaType="user" select="com.yl.dao.IUserDao.queryById"></association>
    </resultMap>
    
    <!--查询所有账户-->
    <select id="queryAll" resultMap="accountUserMap">
        SELECT * FROM account
    </select>

    <!--根据用户id查询账户-->
    <select id="queryByUid" resultType="account" parameterType="int">
        select * from account where uid=#{uid}
    </select>
</mapper>