mybatis Mapper文件标签使用

版权声明：Arno https://blog.csdn.net/yu342107056/article/details/86617184

类型别名,

写在总配置文件中,注意节点元素的顺序或位置

显示mybatis的日志信息

导入jar包 log4j-1.2.16.jar
拷贝log4j.properties到src的根目录中

sql语句块:

用sql标签定义一段sql通过include 引用进来

    <sql id="select_user">
        select 
		    id,
		    username name,
		    userpassword password
	    from t_user 
    </sql> 



   <include refid="select_user"/>

例如：

      <!-- 查询一个数据 -->
	<select id="findUserById"
	        parameterType="java.lang.Integer" 
	        resultType="com.tarena.entity.User">
		<include refid="select_user"></include>
	    where id = #{id}
	</select>

resultMap节点

	<!-- 处理有关结果集列名字跟实体中的getter and setter方法不匹配问题 
	         type="User" java的实体类型（通过<typeAlias type="com.tarena.entity.User"  alias="User"/> 定义出来的User）
	         id="userMap" 唯一一个名称
	         <id  对应的是主键
	         <reslut  普通的属性或结果集的列
	         property:对应java实体类型(字段名称)中的getter and setter
	         column:结果集的列名字,注意不是数据表的字段名（select 后的字段名字，例如uname as name ，这里应该是name）
	    -->  
	    <resultMap type="User" id="userMap">
	    	<id property="id" column="id"/>
	    	<result property="name" column="username" />
	        <result property="password" column="userpassword"/>
	    </resultMap>
	      <!-- 查询一个数据 -->
		<select id="findUserById"
		        parameterType="java.lang.Integer" 
		        resultMap="userMap">
			<include refid="select_user"></include>
		    where id = #{id}
		</select>

动态sql语句

if标签:

        <!-- if标签
       <if  test=" name != null" 从user对象调用getName ,是否为null
       不为null  where age=20 and username=?
       为null    where age=20	
	 -->
	<select id="findUsersByIf"
	        parameterType="User"
	        resultMap="userMap">
		<include refid="select_user"></include>
		where userage=20
		<if test="name != null">
		    and username=#{name}
		</if>  
		<if test="address !=null">
		    and useraddress=#{address}
		</if>      
	</select>

choose when otherwise标签:

	<!-- choose when otherwise
		   有任何一个when条件成立,就拼装对应的sql语句
		  如果所有的when都不成立,就执行otherwise
		 -->
		<select id="findUsersByChoose"
		        parameterType="java.util.Map"
		        resultMap="userMap">
		    <include refid="select_user"></include>        
		    where userage=20
		    <choose>
		    	<when test="uname !=null">
		    	   and username like #{uname}
		    	</when>
		    	<when test="uaddress !=null">
		    	   and useraddress like #{uaddress}
		    	</when>
		    	<otherwise>
		    	   and username like '%a%' and useraddress like '%北京%'
		    	</otherwise>
		    </choose>
		</select>

Where标签

<!-- Where标签 
	 所有的if条件都不成立,就没有where关键字
	 至少有一个if条件成立,就添加where关键字
	 如果where关键字后有 and关键字,则自动去掉and
	-->
	<select id="findUsersByWhere"
	        parameterType="java.util.HashMap"
	        resultMap="userMap">
		<include refid="select_user"></include>
		<where>
		    <if test="uname != null">
		        username like #{uname}
			</if>  
			<if test="uaddress !=null">
			    and useraddress like #{uaddress}
			</if>  
		</where>
	</select>

set 标签:只能用于更新操作

	<!-- set标签 
		  如果所有的if条件都不成立,就不会添加set关键字
		  如果至少有一个if条件成立,就会添加set关键字
		  如果第一个if成立,而第二个if不成立,会自动删除掉末尾的逗号
		-->
		<update id="updateUserBySet" 
		        parameterType="java.util.Map">
			update t_user
				<set>
				   <if test="uname!=null">
				   	  username=#{uname},
				   </if>  
				   <if test="uaddress !=null">
				      useraddress=#{uaddress}
				   </if>
			    </set>
		    where id=#{id}    
		</update>

trim标签(可以替换where标签和set标签)

    <!-- trim  替换 where 
	prefix 前缀  where
	  select * from 表名  where
	prefixOverrides 前缀覆盖
	-->
	<select id="findUsersByTrim1"
	        parameterType="java.util.Map"
	        resultMap="userMap">
		<include refid="select_user"></include>
		<trim prefix="WHERE" prefixOverrides="AND|OR ">
		    <if test="uname != null">
		        username like #{uname}
			</if>  
			<if test="uaddress !=null">
			    and useraddress like #{uaddress}
			</if>  
		</trim>		        
	</select>
	<!-- trim 替换 set 
	prefix  前缀 是set
	suffixOverrides 后缀覆盖  多余的逗号去掉
	-->
	<update id="updateUserByTrim2" 
	        parameterType="java.util.Map">
		update t_user
			<trim prefix="SET" suffixOverrides=",">
			   <if test="uname!=null">
			   	  username=#{uname},
			   </if>  
			   <if test="uaddress !=null">
			      useraddress=#{uaddress}
			   </if>
		    </trim>
	    where id=#{id}    
	</update>

foreach标签:循环

	<!-- foreach标签 
		   delete from t_user where id in(1,2,3)
		-->
		<delete id="deleteUserByForeach"
		        parameterType="java.util.ArrayList">
		     delete from t_user
		     where id in   
		     <foreach  collection="list"
		               item="id"
		               open="("
		               close=")"
		               separator=","
		               index="index">
		          #{id}
		     </foreach>
		</delete>

mybatis多表查询:

mybatis中只有
对一关联
对多关联

<!-- 关联映射关系开始 -->
	<!-- 对一关联
	<association节点  对一关联
	 -->
	<resultMap type="User" id="userMap_orm">
    	<id property="id" column="id"/>
    	<result property="name" column="username" />
        <result property="password" column="userpassword"/>
        <result property="age" column="userage"/>
        <result property="address" column="useraddress"/>
        <association property="group" 
                     javaType="com.arno.entity.Group">
        	<id property="id" column="gid"/>
        	<result property="name" column="groupname"/>
        	<result property="loc" column="grouploc"/>        
        </association>
    </resultMap>
	<select id="findUserById_ORM"
	        parameterType="java.lang.Integer"
	        resultMap="userMap_orm">
		select 
		    u.id,
		    u.username,
		    u.userpassword,
		    u.userage,
		    u.useraddress,
		    g.id gid,
		    g.groupname,
		    g.grouploc
		 from (
		          select * from t_user where id=#{uid}
		      ) u    
		 left join t_group g  on u.group_id=g.id   
	</select>
	<!-- 对多关联 -->
	<resultMap type="com.tarena.entity.Group" id="groupMap_orm">
		<id property="id" column="gid"/>
        <result property="name" column="groupname"/>
        <result property="loc" column="grouploc"/>
        <collection property="users"
                    ofType="com.arno.entity.User"
                    javaType="java.util.List">
        	<id property="id" column="uid"/>
    	    <result property="name" column="username" />
            <result property="password" column="userpassword"/>
            <result property="age" column="userage"/>
            <result property="address" column="useraddress"/>
        </collection>
	</resultMap>
	<select id="findGroupById_ORM"
	        parameterType="java.lang.Integer"
	        resultMap="groupMap_orm">
		select 
		    g.id gid,
		    g.groupname,
		    g.grouploc,
		    u.id uid,
		    u.username,
		    u.userpassword,
		    u.userage,
		    u.useraddress       
	     from (
	             select * from t_group where id=#{gid}
	          ) g
	     left join t_user u on u.group_id=g.id
	</select>
	
	<!-- 关联映射关系结束 -->