最近一直把collection和association弄混，所以為了增強自己的記憶，就擼一個關系出來算是總結罷了
1. 關聯-association
2. 集合-collection
比如同時有user.java和card.java兩個類
user.java如下:
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public class user{private card card_one;private list<card> card_many;} |
在映射card_one屬性時用association標簽, 映射card_many時用collection標簽.
所以association是用于一對一和多對一，而collection是用于一對多的關系
下面就用一些例子解釋下吧
association-一對一
人和身份證的關系
下面是pojo
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public class card implements serializable{ private integer id; private string code;//省略set和get方法.} |
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public class person implements serializable{ private integer id; private string name; private string sex; private integer age; //人和身份證是一對一的關系 private card card;//省略set/get方法.} |
下面是mapper和實現的接口
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package com.glj.mapper;import com.glj.poji.card;public interface cardmapper { card selectcardbyid(integer id);} |
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<?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.glj.mapper.cardmapper"> <select id="selectcardbyid" parametertype="int" resulttype="com.glj.poji.card"> select * from tb_card where id = #{id} </select></mapper> |
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package com.glj.mapper; import com.glj.poji.person; public interface personmapper { person selectpersonbyid(integer id);} |
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<?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.glj.mapper.personmapper"> <resultmap type="com.glj.poji.person" id="personmapper"> <id property="id" column="id"/> <result property="name" column="name"/> <result property="sex" column="sex"/> <result property="age" column="age"/> <association property="card" column="card_id" select="com.glj.mapper.cardmapper.selectcardbyid" javatype="com.glj.poji.card"> </association> </resultmap> <select id="selectpersonbyid" parametertype="int" resultmap="personmapper"> select * from tb_person where id = #{id} </select></mapper> |
personmapper.xml 還使用association的分步查詢。
同理多對一，也是一樣
只要那個pojo出現private card card_one;
即使用association
collection 一對多和association的多對一關系
學生和班級的一對多的例子
pojo類
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package com.glj.pojo; import java.io.serializable;import java.util.list; public class clazz implements serializable{ private integer id; private string code; private string name; //班級與學生是一對多的關系 private list<student> students;//省略set/get方法} |
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package com.glj.pojo;import java.io.serializable;public class student implements serializable { private integer id; private string name; private string sex; private integer age; //學生與班級是多對一的關系 private clazz clazz;//省略set/get方法} |
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<?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.glj.mapper.clazzmapper"> <select id="selectclazzbyid" parametertype="int" resultmap="clazzresultmap"> select * from tb_clazz where id = #{id} </select> <resultmap type="com.glj.pojo.clazz" id="clazzresultmap"> <id property="id" column="id"/> <result property="code" column="code"/> <result property="name" column="name"/> <!-- property: 指的是集合屬性的值, oftype：指的是集合中元素的類型 --> <collection property="students" oftype="com.glj.pojo.student" column="id" javatype="arraylist" fetchtype="lazy" select="com.glj.mapper.studentmapper.selectstudentbyclazzid"> <id property="id" column="id"/> <result property="name" column="name"/> <result property="sex" column="sex"/> <result property="age" column="age"/> </collection> </resultmap></mapper> |
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package com.glj.mapper;import com.glj.pojo.clazz;public interface clazzmapper { clazz selectclazzbyid(integer id);} |
clazzmapper使用到了集合-collection 即為一對多，一個班級面對多個學生
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<?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.glj.mapper.studentmapper"> <select id="selectstudentbyid" parametertype="int" resultmap="studentresultmap"> select * from tb_clazz c,tb_student s where c.id = s.id and s.id = #{id} </select> <select id="selectstudentbyclazzid" parametertype="int" resultmap="studentresultmap"> select * from tb_student where clazz_id = #{id} </select> <resultmap type="com.glj.pojo.student" id="studentresultmap"> <id property="id" column="id"/> <result property="name" column="name"/> <result property="sex" column="sex"/> <result property="age" column="age"/> <association property="clazz" javatype="com.glj.pojo.clazz"> <id property="id" column="id"/> <result property="code" column="code"/> <result property="name" column="name"/> </association> </resultmap></mapper> |
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package com.glj.mapper;import com.glj.pojo.student;public interface studentmapper { student selectstudentbyid(integer id); } |
studentmapper則是與班級為多對一關系，所以使用了關聯-association
嗯，希望我以后又不記得二者的關系時,能感謝現在總結的自己
附上一張mybatis的類型別名圖
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
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