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>

来源：https://blog.csdn.net/zlc819240815/article/details/83008475