mybatis mapper标签

多表连接


<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE mapper SYSTEM "http://mybatis.org/dtd/mybatis-3-mapper.dtd" PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN">

-<mapper namespace="com.gem.demo.mapper.ProductMapper">


-<resultMap id="ProductMap" type="Product">

<id property="id" column="id"/>

<!-- 主键字段 -->


<result property="pname" column="pname"/>

<!-- 普通字段 -->


<result property="pimg" column="pimg"/>

<result property="price" column="price"/>

<result property="info" column="info"/>

<result property="ptype" column="ptype"/>

<!-- 1端 -->



-<association property="type" javaType="ProductType">

<id property="id" column="typeid"/>

<result property="typename" column="typename"/>

</association>

</resultMap>


-<select id="findAll" resultMap="ProductMap">

<!-- 多表连接查询 -->

select t1.*,t2.id typeid,t2.typename from product t1 left join producttype t2 on t1.ptype=t2.id 
</select>

</mapper>

多表连接，一对多

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.gem.demo.mapper.ProductTypeMapper">
    <resultMap type="ProductType" id="ProductTypeMap">
        <id column="typeid" property="id"/>
        <result column="typename" property="typename"/>
        <!-- 一对多 -->
        <collection property="products" ofType="Product">
            <id column="id" property="id"/>
            <result column="pname" property="pname"/>
            <result column="pimg" property="pimg"/>
            <result column="price" property="price"/>
            <result column="info" property="info"/>
            <result column="ptype" property="ptype"/>
        </collection>
    </resultMap>
    <select id="findAll" resultMap="ProductTypeMap">
        <!--1对多查询 -->
        select t1.id typeid,t1.typename,t2.* from  producttype t1 left join product t2 on t1.id=t2.ptype
    </select>

</mapper>

<select id="findAll" resultMap="ProductTypeMap"><!--1对多查询 --> select t1.id typeid,t1.typename,t2.* from producttype t1 left join product t2 on t1.id=t2.ptype </select></mapper>

懒加载


<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.gem.demo.mapper.ProductMapper">
    <resultMap type="Product" id="ProductMap">
        <id column="id" property="id"/><!-- 主键字段 -->
        <!-- 普通字段  column :查询结果中的字段名 property：实体中的属性名-->
        <result column="pname" property="pname"/>
        <result column="pimg" property="pimg"/>
        <result column="price" property="price"/>
        <result column="info" property="info"/>
        <result column="ptype" property="ptype"/>
        <!-- 懒加载 -->
        <association property="type" javaType="ProductType"
            select="com.gem.demo.mapper.ProductTypeMapper.selectById" column="ptype"></association>
        
    </resultMap>
    <select id="findAll" resultMap="ProductMap">
        select  * from product
    </select>

</mapper>

#{}、${}的用法，动态sql

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace:Mapper（DAO）接口的全路径 -->
<mapper namespace="com.gem.demo.mapper.ProductMapper">
    <!--id: 同一个namespace下id唯一  接口中的方法名
        resultType：查询结果映射的实体类的全类名
                    在mybatis的核心配置文件中定义别名
                    映射为别名
      -->
    <select id="findAll" resultType="Product">
        select * from product
    </select>
    <!-- 
        parameterType:参数类型
        sql语句中
         #{}设置参数  底层 jdbc psmt  预编译  ?  "%"?"%"  ptype=?
        ${}  字符串值直接拼接  没有? 
        #{} ${}区别 
     -->
    <select id="selectBytype" resultType="Product" parameterType="int">
        select * from product where ptype=#{ptype}
    </select>
    <!-- 模糊查询 
        select * from product where pname like '%${value}%'
        select * from product where pname like "%"#{name}"%"
        select * from product where pname like "%"#{value}"%"
        select * from product where pname like concat("%",#{name},"%")
        select * from product where pname like concat("%","${value}","%")
        
        
        concat:字符串拼接函数(mysql)
    
    -->
    <select id="selectByName" resultType="Product" >
        select * from product where pname like concat("%",'${value}',"%")
    </select>
    <select id="getToal" resultType="int" >
        select count(id) from product
    </select>
    <!-- 动态sql -->
    <!-- <select id="selectByNameAndType" resultType="Product">
        select * from product where 1=1
        <if test="pname!=null and pname !=''" >
            and pname like "%"#{pname}"%"
        </if>
        <if test="ptype!=null and ptype!=0">
                and ptype=#{ptype}
        </if>
    </select> -->
    <!-- sql片段 -->
    <sql id="defaultQueryProduct">
        select * from product
    </sql>
    <select id="selectByNameAndType" resultType="Product">
        <!-- 引用sql片段 -->
        <include refid="defaultQueryProduct"></include>
        <where>
            <if test="pname!=null and pname !=''" >
                and pname like "%"#{pname}"%"
            </if>
            <if test="ptype!=null and ptype!=0">
                and ptype=#{ptype}
            </if>
        </where>
    </select>
    <!-- 分类1或者分类3的数据  ptype in(1,3) 
        foreach:遍历 list  set  map  array
        select * from product
         where 
        ptype in(?,?)
        foreach: 用于in查询
            属性：collection 集合类型  list...
                    item:集合元素
                    index：元素的索引
                    open：遍历集合之前的部分
                    close：遍历集合之后的部分
                    separator：元素之间的分割符
                
     -->
     <select id="selectBytypes" resultType="Product">
         <include refid="defaultQueryProduct"></include>
         <where>
             <foreach collection="list" item="type" open="ptype in (" separator="," close=")"> 
                 #{type}
             </foreach>
         </where>
     </select>
</mapper>