如何编写MyBatis多表关联的mapper文件操作语句？

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两表SystemParam（系统参数表）与Suit（主题）关联，其中SystemParam与Suit是多对一关系。Suit的higherSuit字段是Suit的父级及主题id，且是唯一标识，需自连接查询，因为存在重名，故对父表sql字段加别名。mapper方法名Sy。

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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