mybatis中@param的使用与否

1、不使用@param

　　DAO层：List<ShopCategory> queryShopCategory(ShopCategory shopCategory);：以对象为参数

　　mapper.xml：

<select id="queryShopCategory" resultType="com.imooc.o2o.entity.ShopCategory">
		SELECT
		shop_category_id,
		shop_category_name,
		shop_category_desc,
		shop_category_img,
		priority,
		create_time,
		last_edit_time,
		parent_id
		FROM
		tb_shop_category
		<where>
			<!-- <if test="shopCategoryCondition.parent != null">
				and parent_id = #{shopCategoryCondition.parent.shopCategoryId}
			</if> -->
			<if test="parent != null">
				and parent_id = #{parent.shopCategoryId}
			</if>
		</where>
		ORDER BY 
		priority DESC
	</select>

　　DO层：

package com.imooc.o2o.entity;

import java.util.Date;

public class ShopCategory {
    
    private Long shopCategoryId;
    private String shopCategoryName;
    private String shopCategoryDesc;
    private String shopCategoryImg;
    private Integer priority;
    private Date createTime;
    private Date lastEditTime;
    private ShopCategory parent;
    public Long getShopCategoryId() {
        return shopCategoryId;
    }
    public void setShopCategoryId(Long shopCategoryId) {
        this.shopCategoryId = shopCategoryId;
    }
    public String getShopCategoryName() {
        return shopCategoryName;
    }
    public void setShopCategoryName(String shopCategoryName) {
        this.shopCategoryName = shopCategoryName;
    }
    public String getShopCategoryDesc() {
        return shopCategoryDesc;
    }
    public void setShopCategoryDesc(String shopCategoryDesc) {
        this.shopCategoryDesc = shopCategoryDesc;
    }
    public String getShopCategoryImg() {
        return shopCategoryImg;
    }
    public void setShopCategoryImg(String shopCategoryImg) {
        this.shopCategoryImg = shopCategoryImg;
    }
    public Integer getPriority() {
        return priority;
    }
    public void setPriority(Integer priority) {
        this.priority = priority;
    }
    public Date getCreateTime() {
        return createTime;
    }
    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    public Date getLastEditTime() {
        return lastEditTime;
    }
    public void setLastEditTime(Date lastEditTime) {
        this.lastEditTime = lastEditTime;
    }
    public ShopCategory getParent() {
        return parent;
    }
    public void setParent(ShopCategory parent) {
        this.parent = parent;
    }
    @Override
    public String toString() {
        return "ShopCategory [shopCategoryId=" + shopCategoryId + ", shopCategoryName=" + shopCategoryName
                + ", shopCategoryDesc=" + shopCategoryDesc + ", shopCategoryImg=" + shopCategoryImg + ", priority="
                + priority + ", createTime=" + createTime + ", lastEditTime=" + lastEditTime + ", parent=" + parent
                + "]";
    }
    
    
}

2.使用@param

　　DAO层：

List<ShopCategory> queryShopCategory(@Param("shopCategoryCondition") ShopCategory shopCategory);

　　mapper.xml：

　　

<?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.imooc.o2o.dao.ShopCategoryMapper">
    <select id="queryShopCategory" resultType="com.imooc.o2o.entity.ShopCategory">
        SELECT
        shop_category_id,
        shop_category_name,
        shop_category_desc,
        shop_category_img,
        priority,
        create_time,
        last_edit_time,
        parent_id
        FROM
        tb_shop_category
        <where>
            <if test="shopCategoryCondition.parent != null">
                and parent_id = #{shopCategoryCondition.parent.shopCategoryId}
            </if>
        </where>
        ORDER BY 
        priority DESC
    </select>
</mapper>

由此可以看出，mybatis在xml中做值的注入时，若是不使用@param，则若参数为对象，则在#{}中则直接写对象中的属性。无法根据对象来绑定。例如上例中的and parent_id = #{parent.shopCategoryId}。参数为ShopCategory。但是由于没有用

@param做参数别名，因此在#{}无法直接引用参数，只能直接通过对象参数的属性来进行#{}注入。

但是如果使用了@param。则对象参数在进行#{}注入时可以使用别名。例如下例子中 shopCategoryCondition就是DAO层定义的方法中的参数shopCategory的别名

  <if test="shopCategoryCondition.parent != null">
      and parent_id = #{shopCategoryCondition.parent.shopCategoryId}
  </if>