mybatis中@param的使用与否
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：
1 package com.imooc.o2o.entity; 2 3 import java.util.Date; 4 5 public class ShopCategory { 6 7 private Long shopCategoryId; 8 private String shopCategoryName; 9 private String shopCategoryDesc; 10 private String shopCategoryImg; 11 private Integer priority; 12 private Date createTime; 13 private Date lastEditTime; 14 private ShopCategory parent; 15 public Long getShopCategoryId() { 16 return shopCategoryId; 17 } 18 public void setShopCategoryId(Long shopCategoryId) { 19 this.shopCategoryId = shopCategoryId; 20 } 21 public String getShopCategoryName() { 22 return shopCategoryName; 23 } 24 public void setShopCategoryName(String shopCategoryName) { 25 this.shopCategoryName = shopCategoryName; 26 } 27 public String getShopCategoryDesc() { 28 return shopCategoryDesc; 29 } 30 public void setShopCategoryDesc(String shopCategoryDesc) { 31 this.shopCategoryDesc = shopCategoryDesc; 32 } 33 public String getShopCategoryImg() { 34 return shopCategoryImg; 35 } 36 public void setShopCategoryImg(String shopCategoryImg) { 37 this.shopCategoryImg = shopCategoryImg; 38 } 39 public Integer getPriority() { 40 return priority; 41 } 42 public void setPriority(Integer priority) { 43 this.priority = priority; 44 } 45 public Date getCreateTime() { 46 return createTime; 47 } 48 public void setCreateTime(Date createTime) { 49 this.createTime = createTime; 50 } 51 public Date getLastEditTime() { 52 return lastEditTime; 53 } 54 public void setLastEditTime(Date lastEditTime) { 55 this.lastEditTime = lastEditTime; 56 } 57 public ShopCategory getParent() { 58 return parent; 59 } 60 public void setParent(ShopCategory parent) { 61 this.parent = parent; 62 } 63 @Override 64 public String toString() { 65 return "ShopCategory [shopCategoryId=" + shopCategoryId + ", shopCategoryName=" + shopCategoryName 66 + ", shopCategoryDesc=" + shopCategoryDesc + ", shopCategoryImg=" + shopCategoryImg + ", priority=" 67 + priority + ", createTime=" + createTime + ", lastEditTime=" + lastEditTime + ", parent=" + parent 68 + "]"; 69 } 70 71 72 }
2.使用@param
DAO层：
List<ShopCategory> queryShopCategory(@Param("shopCategoryCondition") ShopCategory shopCategory);
mapper.xml：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 3 "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> 4 <mapper namespace="com.imooc.o2o.dao.ShopCategoryMapper"> 5 <select id="queryShopCategory" resultType="com.imooc.o2o.entity.ShopCategory"> 6 SELECT 7 shop_category_id, 8 shop_category_name, 9 shop_category_desc, 10 shop_category_img, 11 priority, 12 create_time, 13 last_edit_time, 14 parent_id 15 FROM 16 tb_shop_category 17 <where> 18 <if test="shopCategoryCondition.parent != null"> 19 and parent_id = #{shopCategoryCondition.parent.shopCategoryId} 20 </if> 24 </where> 25 ORDER BY 26 priority DESC 27 </select> 28 </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>
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