mybatis 多表关联mapper文件写法操作

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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