Mybatis的学习-day02

Mybatis的学习-day02

1.输入参数和输出参数详解

• 传入简单类型

  
      <select id="selectUserById" parameterType="Integer" 
      resultType="cn.xiaozou.entity.User">
              select * from user where id=#{id}
  select>
  

• 传入pojo对象

  	
  	<insert id="insertUser" parameterType="cn.xiaozou.entity.User">
  		
  		<selectKey keyProperty="id" order="AFTER" keyColumn="id"
  			resultType="Integer">
  			select LAST_INSERT_ID();
  		selectKey>
  		insert into user(id,username,sex,birthday,address)
  		values(#{id},#{username},#{sex},#{birthday},#{address})
  	insert>
  

• 传入pojo包装对象

  
  	
  	<select id="selectByIds" parameterType="QueryVo" resultType="User">
  		select * from user
  		where id in
  		<foreach collection="ids" open="(" close=")" separator="," item="id">
  			#{id}
  		foreach>
  	select>
  

• 输出简单类型

  	
  	<select id="countNum" resultType="Integer">
  		select count(*) from user
  	select>
  

• 输出pojo对象

  <select id="selectUserById" parameterType="Integer"
  		resultType="cn.xiaozou.entity.User">
  		select * from user where id=#{id}
  select>
  

2.ResultMap详解

• resultMap:当数据库中表的字段和实体类的属性不一致时使用，还有进行一对多，或者多对一映射时使用

  
  	<resultMap type="orders" id="OrdersMapper">
  		
  		<result column="user_id" property="userId"/>
  	resultMap>
  	<select id="selectById" parameterType="Integer" resultMap="OrdersMapper">
  		select * from orders where id=#{id}
  	select>
  

3.动态SQL

• If标签：可以进行条件判断，set标签去除后逗号

  
  	<update id="updateUserBySelective" parameterType="User">
  		update user
  		<set>
  			<if test="username!=null">
  				username=#{username},
  			if>
  			<if test="sex!=null">
  				sex=#{sex},
  			if>
  			<if test="birthday!=null">
  				birthday=#{birthday},
  			if>
  			<if test="address!=null">
  				address=#{address},
  			if>
  		set>
  		where id=#{id}
  	update>
  

• foreach标签：遍历传入的集合或者数组

  
  	<select id="selectByIds" parameterType="QueryVo" resultType="User">
  		select * from user
  		where id in
  		<foreach collection="ids" open="(" close=")" separator=","
  			item="id">
  			#{id}
  		foreach>
  	select>
  

• where标签：去除前and

  	
  	<select id="selectByExample" parameterType="User" resultType="User">
  		select * from user 
  			<where>
  				<if test="id!=null">
  					and id=#{id}
  				if>
  				<if test="username!=null">
  					and username like "%"#{username}"%"
  				if>
  			where>
  	select>
  

• sql片段标签：可以将重复的sql提取出来，使用时用include即可，达到代码复用的效果

  	<sql id="selectAll">
  	 	select * from user
  	 sql>
  	<select id="selectByExample" parameterType="User" resultType="User">
  		<include refid="selectAll">include>
  			<where>
  				<if test="id!=null">
  					and id=#{id}
  				if>
  				<if test="username!=null">
  					and username like "%"#{username}"%"
  				if>
  			where>
  	select>
  

  4.关联查询

  4.1一对一查询

  
  	<resultMap type="Orders" id="SingleToSingle">
  		<id property="id" column="id"/>
  		<result property="number" column="number"/>
  		<result property="createtime" column="createtime"/>
  		
  		<association property="user" javaType="User">
  			<id property="id" column="user_id"/>
  			<result property="username" column="username"/>
  		association>
  		
  	resultMap>
  	<select id="selectSingelToSingle" resultMap="SingleToSingle">
  			select 
  				o.id,o.number,o.createtime,o.user_id,
  	  			u.username
  			from orders o
  			LEFT JOIN	user u
  			on o.user_id=u.id;
  	select>
  

  4.2一对多查询

  
  	
  	<resultMap type="User" id="oneToManyMapper">
  		<id column="id" property="id"/>
  		<result column="username" property="username"/>
  		
  		<collection property="orders" ofType="Orders">
  			<id column="id" property="id">id>
  			<result column="number" property="number"/>
  			<result column="createtime" property="createtime"/>
  		collection>
  	resultMap>
  	
  	<select id="selectOneToMany" resultMap="oneToManyMapper">
  		select 
  				u.id,u.username,
  		o.number,o.createtime,o.id
  			from user u
  			LEFT JOIN	orders o
  			on u.id=o.user_id;
  	select>