mybatis 多表关联mapper文件写法操作
作者：林奇lc
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两张表SystemParam（系统参数表） Suit （主题）
SystemParam 与 Suit 是多对一
Suit 的higerSuit字段是Suit 的父及主题id 是多对一，需要自连接查询，因为重名所以父表sql字段加别名
mapper方法
Systemparam selectJoinSuit(String strparamcode);
Po类
public class Systemparam {
//ManyToOne "主题"
private Suit suitobj;
private String strparamcode;
private String strenable;
private String strparamname;
//suit表主键
private String suit;
private String strparamvalue;
｝
public class Suit {
//ManyToOne
private Suit suit;
//主键
private String strsuitcode;
private String strsuitname;
//父级id
private String higersuit;
｝
resultMap的写法
<resultMap id="BaseResultMap" type="net.transino.model.Systemparam" > <id column="strParamCode" property="strparamcode" jdbcType="VARCHAR" /> <result column="strEnable" property="strenable" jdbcType="VARCHAR" /> <result column="strParamName" property="strparamname" jdbcType="VARCHAR" /> <result column="suit" property="suit" jdbcType="VARCHAR" /> </resultMap>
resultMap 使用extends 继承上级map
<resultMap id="ResultMapWithBLOBs" type="net.transino.model.Systemparam" extends="BaseResultMap" > <result column="strParamValue" property="strparamvalue" jdbcType="LONGVARCHAR" /> </resultMap> <resultMap id="JoinsuitMap" type="net.transino.model.Systemparam" extends="ResultMapWithBLOBs" > <association property="suitobj" javaType="Suit"> <id column="strSuitCode" property="strsuitcode" jdbcType="VARCHAR" /> <result column="strSuitName" property="strsuitname" jdbcType="VARCHAR" /> <result column="higerSuit" property="higersuit" jdbcType="VARCHAR" /> <association property="suit" javaType="Suit"> <id column="pstrSuitCode" property="strsuitcode" jdbcType="VARCHAR" /> <result column="pstrSuitName" property="strsuitname" jdbcType="VARCHAR" /> <result column="phigerSuit" property="higersuit" jdbcType="VARCHAR" /> </association> </association> </resultMap>
select写法
<select id="selectJoinSuit" resultMap="JoinsuitMap" parameterType="java.lang.String">
select
systempara0_.*,
suit1_.*,
suit2_.strSuitCode pstrSuitCode,
suit2_.strSuitName pstrSuitName,
suit2_.higerSuit phigerSuit
from SystemParam systempara0_
LEFT OUTER JOIN
Suit suit1_
ON systempara0_.suit=suit1_.strSuitCode
LEFT OUTER JOIN
Suit suit2_
ON suit1_.higerSuit=suit2_.strSuitCode
WHERE
systempara0_.strParamCode=#{strparamcode,jdbcType=VARCHAR}
</select>
补充知识：Mybatis中resultMap标签实现多表查询（多个对象）
1 n+1
1 在teacher中添加List student，
public class Teacher {
private int id;
private String name;
private List<Student> list;
2 在studentMapper.xml中添加通过tid查询
<select id="selByTid" resultType="Student" parameterType="int">
select * from student where tid=#{0}
</select>
3 在TeacherMapper.xml中添加查询全部
<resultMap type="Teacher" id="mymap1"> <id column="id" property="id"/> <result column="name" property="name"/> <collection property="list" ofType="Student" select="com.bjsxt.mapper.StudentMapper.selByTid" column="id"></collection> </resultMap> <select id="selAll" resultMap="mymap1"> select * from teacher </select>
其中collection是当属性为集合类型时使用的标签
2 多表联合
<resultMap type="Teacher" id="stumap1"> <id column="tid" property="id"/> <result column="tname" property="name"/> <collection property="list" ofType="Student"> <id column="sid" property="id"/> <result column="sname" property="name"/> <result column="age" property="age"/> <result column="tid" property="tid"/> <association property="teacher" select="com.bjsxt.mapper.TeacherMapper.selById" column="tid"></association> </collection> </resultMap> <select id="selAll1" resultMap="stumap1"> select t.id tid,t.name tname,s.id sid,s.name sname,age,tid from teacher t left join student s on t.id=s.tid </select>
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