mybatis實現一對一延遲載入

阿新 • • 發佈：2020-10-21

mybatis實現一對一延遲載入

需求：使用者和賬戶一對一關係，查詢賬戶時實現使用者的延遲載入

思路：根據id查詢，需要延遲載入的一方

1、使用者實體類

package com.yl.bean;

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

/**
 * 使用者實體類
 */
public class User implements Serializable {
    private Integer id;//id
    private String username;//使用者名稱
    private Date birthday;//生日
    private String sex;//性別
    private String address;//地址
    private Account account;//使用者所擁有的賬戶

    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 Account getAccount() {
        return account;
    }

    public void setAccount(Account account) {
        this.account = account;
    }

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

2、賬戶實體類

package com.yl.bean;

import java.io.Serializable;

/**
 * 賬戶實體類
 */
public class Account implements Serializable {
    private Integer id;//賬戶id
    private Integer uid;//使用者id
    private Double money;//餘額
    private User user;//賬戶所屬使用者

    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、使用者持久層介面

package com.yl.dao;

import com.yl.bean.User;

import java.util.List;

/**
 * 使用者持久層介面
 */
public interface IUserDao {

    /**
     * 查詢所有使用者
     */
    List<User> queryAll();

    /**
     * 根據id查詢使用者
     */
    User queryById(int id);

}

4、賬戶持久層介面

package com.yl.dao;

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

import java.util.List;

/**
 * 賬戶持久層介面
 */
public interface IAccountDao {

    /**
     * 查詢所有賬戶
     */
    List<Account> queryAll();
}

5、全域性配置檔案

<?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>
        <!--開啟延遲載入-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

    <!--配置別名-->
    <typeAliases>
        <package name="com.yl.bean"/>
    </typeAliases>

    <!--配置mybatis環境-->
    <environments default="mysql">
        <!--配置mysql環境-->
        <environment id="mysql">
            <!--事務型別-->
            <transactionManager type="JDBC"></transactionManager>
            <!--資料來源-->
            <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>

    <!--指定對映配置檔案位置-->
    <mappers>
        <mapper resource="IUserDao.xml"></mapper>
        <mapper resource="IAccountDao.xml"></mapper>
    </mappers>
</configuration>

6、使用者對映配置檔案

<?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">
    <!--配置使用者實體類和資料庫的對應資訊-->
    <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>
        <!--一對一對映關係-->
        <collection property="account" ofType="com.yl.bean.Account">
            <id property="id" column="id"></id>
            <result property="uid" column="uid"></result>
            <result property="money" column="money"></result>
        </collection>
    </resultMap>

    <!--查詢所有使用者-->
    <select id="queryAll" resultMap="userMap">
        SELECT * FROM USER u LEFT OUTER JOIN account a ON u.`id`=a.`UID`
    </select>
    <!--根據id查詢使用者-->
    <select id="queryById" resultType="user" parameterType="int">
        select * from user where id=#{id}
    </select>
</mapper>

7、賬戶對映配置檔案

<?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屬性對應資料庫資訊-->
    <resultMap id="accountUserMap" type="account">
        <id property="id" column="id"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
        <!--通過id查詢使用者-->
        <association property="user" column="uid" javaType="user" select="com.yl.dao.IUserDao.queryById"></association>
    </resultMap>
    
    <!--查詢所有賬戶-->
    <select id="queryAll" resultMap="accountUserMap">
        SELECT * FROM account
    </select>

</mapper>