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Mybatis中的assocication和collection

 5 years ago
source link: https://aodeng.cc/archives/associcationcollectio?amp%3Butm_medium=referral
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Mybatis中的assocication和collection

啊日谁行，抗内可行，第一个是用来关联实体类的，第二个是用来关联集合的，也就是打脑壳的一对一(assocication)，一对多(collection)

使用

举个简单的例子，公司项目虽然复杂，其实只要通过简单的例子理解了，再复杂也不带怕的

has one

一个人一张身份证

//这是一个人，加一张身份证
public class User {
    private String userName;
    private Card card;
}
//这是 一张身份证
public class Card {
    private String cardNum;//身份证号
}
//sql
<select id="findOneUserById" parameterType="int" resultMap="userMap">
    SELECT 
                u.*,
                c.*
                FROM user u
                left join card c on c.id=u.id
                where 1=1  and u.Id=#{id}
</select>
//map    
<resultMap type="User" id="userMap">
   <result property="userName"  column="user_name"/>
   <association property="card"  column="card_id"  javaType="Card">
       <id property="cardId"  column="card_id"/>
       <result property="cardNum"  column="card_num"/>
   </association>
</resultMap>

has many

见我上一篇文章即可

https://aodeng.cc/archives/mybatisgaoji

我的博客：https://aodeng.cc 我的公众号：低调小熊猫 我的QQ群：756796932


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