association与collection

 关联-association

 集合-collection

association是用于一对一和多对一，而collection是用于一对多的关系

多对一：

 <resultMap type="Product" id="productBean">
            <id column="pid" property="id" />
            <result column="pname" property="name" />
            <result column="price" property="price" />
     
            <!-- 多对一的关系 -->
            <!-- property: 指的是属性名称, javaType：指的是属性的类型 -->
            <association property="category" javaType="Category">
                <id column="cid" property="id"/>
                <result column="cname" property="name"/>
            </association>
        </resultMap>
     

一对多

  <resultMap type="Category" id="categoryBean">
            <id column="cid" property="id" />
            <result column="cname" property="name" />
     
            <!-- 一对多的关系 -->
            <!-- property: 指的是集合属性的值, ofType：指的是集合中元素的类型 -->
            <collection property="products" ofType="Product">
                <id column="pid" property="id" />
                <result column="pname" property="name" />
                <result column="price" property="price" />
            </collection>
        </resultMap>
     

多对多：

 <resultMap type="Order" id="orderBean">
            <id column="oid" property="id" />
            <result column="code" property="code" />
             
            <collection property="orderItems" ofType="OrderItem">
                <id column="oiid" property="id" />
                <result column="number" property="number" />
                <association property="product" javaType="Product">
                    <id column="pid" property="id"/>
                    <result column="pname" property="name"/>
                    <result column="price" property="price"/>
                </association>               
            </collection>
        </resultMap>