mybatis映射文件标签总结

动态sql：

1.if

  <select id="findUsers1" parameterType="cn.flyingd.domain.User">
      select * from user where 1=1
      <if test="userName !=null ">
          and username = #{userName}
      </if>
		
      <if test="userSex !=null ">
          and usersex = #{userSex}
      </if>	
  </select>

2.where

  <select id="findUsers1" parameterType="cn.flyingd.domain.User">
      select * from user 
      <where>
          <if test="userName !=null ">
              and username = #{userName}
          </if>
			
          <if test="userSex !=null ">
              and usersex = #{userSex}
          </if>
      </where>	
  </select>

3.foreach

  <select id="findUsers1" parameterType="cn.flyingd.domain.QueryVo">
      select * from user 
      <where>
          <foreach collection="ids" open="and id in (" close=")" sperator="," item="aaa" >
              #{aaa}
          </foreach>
      </where>
  </select>

4.sql片段

  <sql id="abc" >
      select * from user
  </sql>

  <select id="findUsers1" parameterType="cn.flyingd.domain.QueryVo">
       <include refid="abc" />
      <where>
          <foreach collection="ids" open="and id in (" close=")" sperator="," item="aaa" >
              #{aaa}
          </foreach>
      </where>
  </select>

5.Mybatis，多对一，看成了一对一
```
      public class Account {
  		private User user1;  //持有引用
  	}
```
```
      public class User {
  	}
```
- 映射文件IAccountDao.xml ```xml
``` select a.*,u.id uid,u.address userAddress,u.sex userSex from account a left join user u on a.uid = u.id

6.一对多

      public class User {
  		private List<Account> accountList;
  	}

  	public class Account {
  	}

映射文件IUserDao.xml ```xml

``` select u.*,a.id aid,a.uid,a.money from user u left join account a on u.id = a.uid

7.Mybatis，多对多，看成一对多
```
      public class User {
  		private List<Role> roleList;
  	} 
```
```
      public class Role {
  	}
```
- IUserDao.xml ```xml
</resultMap> ``` select u.*,r.id rid,r.role_name from user u left join user_role ur on u.id= ur.uid left join role r on ur.rid = r.id

动态sql

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