• 在 Mapper xml 中的标签里使用可以完成 1对1 关联查询

• 在 Mapper xml 中的标签里使用可以完成 1对多 关联查询

//sql
create table user (
id int primary key,
name varchar(400)
);
insert user info VALUES(1, 'ConstXiong1');

create table info (
user_id int primary key,
name varchar(400)
);
insert into info VALUES(1, '大熊');

create table article (
user_id int,
title varchar(400)
);
insert into article VALUES(1, '文章1');
insert into article VALUES(1, '文章2');




//Mapper xml
<!-- 1对1 -->
<select id="selectUserWithInfo" resultMap="UserWithInfo">
    select user.id, user.name, info.user_id, info.name as info_name from user,info where user.id = info.user_id
</select>

<!-- 1对多 -->
<select id="selectUserWithArticles" resultMap="UserWithArticles">
    select user.id, user.name, article.user_id, article.title from user,article where user.id = article.user_id
</select>

<resultMap id="UserWithInfo" type="constxiong.po.User">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <!-- 1对1 -->
    <association property="info" javaType="constxiong.po.Info">
        <id property="userId" column="user_id"/>
        <result property="name" column="info_name"/>
    </association>
</resultMap>

<resultMap id="UserWithArticles" type="constxiong.po.User">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <!-- 1对多 -->
    <collection property="articles" ofType="constxiong.po.Article">
        <result property="userId" column="user_id"/>
        <result property="title" column="title"/>
    </collection>
</resultMap>

//User.java
/**
 * 用户表模型
 */
public class User {
    private Integer id;

    private String name;

    private String mc;

    private Info info;

    private List<Article> articles;

    public User() {
    }

    public User(Integer id, String name) {
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getMc() {
        return mc;
    }

    public void setMc(String mc) {
        this.mc = mc;
    }

    public Info getInfo() {
        return info;
    }

    public void setInfo(Info info) {
        this.info = info;
    }

    public List<Article> getArticles() {
        return articles;
    }

    public void setArticles(List<Article> articles) {
        this.articles = articles;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", mc='" + mc + '\'' +
                ", info=" + info +
                ", articles=" + articles +
                '}';
    }
}


//测试代码
System.out.println("------ selectUserWithInfo ------");
user = userMapper.selectUserWithInfo();
System.out.println(user);

System.out.println("------ selectUserWithArticles ------");
user = userMapper.selectUserWithArticles();
System.out.println(user);

//打印
------ selectUserWithInfo ------
User{id=1, name='ConstXiong1', mc='null', info=Info{userId=1, name=大熊}, articles=null}
------ selectUserWithArticles ------
User{id=1, name='ConstXiong1', mc='null', info=null, articles=[Article{userId=1, title='文章1'}, Article{userId=1, title='文章2'}]}

完整 Demo：

https://javanav.com/val/a9fe4555c1614b40b0da07afeabf2a66.html