mybatis多对一

public class Product {
    private int id;
    private String name;
    private float price;
    private Category category;
     
    public Category getCategory() {
        return category;
    }
    public void setCategory(Category category) {
        this.category = category;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    @Override
    public String toString() {
        return "Product [id=" + id + ", name=" + name + ", price=" + price + "]";
    }
 
}

public class Category {
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
   
    @Override
    public String toString() {
        return "Category [id=" + id + ", name=" + name + "]";
    }
     
}

提供Product.xml，通过listProduct配置关联查询的sql语句。
然后通过resultMap ，进行字段和属性的对应。
使用association 进行多对一关系关联，指定表字段名称与对象属性名称的一一对应关系
注： Category的id 字段 和Product的id字段同名，Mybatis不知道谁是谁的，所以需要通过取别名cid,pid来区分。
name字段同理。
<?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.how2java.pojo">
        <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>
     
        <!-- 根据id查询Product, 关联将Orders查询出来 -->
        <select id="listProduct" resultMap="productBean">
            select c.*, p.*, c.id ‘cid‘, p.id ‘pid‘, c.name ‘cname‘, p.name ‘pname‘ from category_ c left join product_ p on c.id = p.cid
        </select>   
    </mapper>