mybatis collection select(mybatis支持的多表查询有哪几种方式)

在使用select语句时，有时候需要查询两个表，可以使用表连接进行查询，也可以用mybatis给我们提供的collection标签
collection标签是在结果集映射的时候添加，也就是在resultMap标签添加，且不能放在result标签前面
collection标签属性有许多，但是基本用法只需要property、select、column
例如：

上面所写是关于两个表各自查询，然后通过关联的属性获取另外实体类的值，总体代码这里就不贴了，只要记住collection 是关于两个表各自查询，然后调用此标签，association是用来sql语句表连接查询的时候使用，可在这个标签下再次写入结果集映射
mybatis官网上的结果映射resultMap各个属性详解点击跳转

这里是详细代码，数据库表就不贴了
（1）两个实体类

package com.csh.bean;

public class Activity {
    private Integer activityId;
    private OrdinaryUser ordinaryUser;
    private String theCityName;
    private String title;
    private String content;


    public Integer getActivityId() {
        return activityId;
    }

    public void setActivityId(Integer activityId) {
        this.activityId = activityId;
    }

    public OrdinaryUser getOrdinaryUser() {
        return ordinaryUser;
    }

    public void setOrdinaryUser(OrdinaryUser ordinaryUser) {
        this.ordinaryUser = ordinaryUser;
    }

    public String getTheCityName() {
        return theCityName;
    }

    public void setTheCityName(String theCityName) {
        this.theCityName = theCityName;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    @Override
    public String toString() {
        return "Activity{" +
                "activityId=" + activityId +
                ", ordinaryUser=" + ordinaryUser +
                ", theCityName='" + theCityName + ''' +
                ", title='" + title + ''' +
                ", content='" + content + ''' +
                '}';
    }
}

package com.csh.bean;

import java.util.Date;

public class OrdinaryUser {
    private String userAccount;
    private String pwd;
    private Integer sex;
    private Date birthday;


    public String getUserAccount() {
        return userAccount;
    }

    public void setUserAccount(String userAccount) {
        userAccount = userAccount;
    }

    public String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public Integer getSex() {
        return sex;
    }

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

    public Date getBirthday() {
        return birthday;
    }

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

    @Override
    public String toString() {
        return "OrdinaryUser{" +
                "UserAccount='" + userAccount + ''' +
                ", pwd='" + pwd + ''' +
                ", sex=" + sex +
                ", birthday=" + birthday +
                '}';
    }
}

（2）dao层两个接口

public interface ActivityDao {
    public Activity selectAll(Integer activityId);
}

public interface OrdinaryUserDao {
    public OrdinaryUser selectAll(String userAccount);
}

（3）两个映射文件

    
        select * from activity where activity_id  = #{activityId}
    
    
        
        
        
        




        
        

    

 



    
        select * from ordinary_user where user_account = #{userAccount}