问题描述：因为领导的一个需求，需要用到使用resultMap，很久没使用了，结果就除了点意外。就记录下这个问题
准备两个类：author(作者)和book（书），数据库创建对应的author->book一对多的数据
@Data
public class Author {
private Integer id;
private String name;
private String phone;
private String address;
private List<Book> books;
}
@Data
public class Book {
private Integer id;
private String name;
private String press;
private BigDecimal price;
private Integer authorId;
}
开始的Mapper.xml文件
<resultMap id="bookMap" type="com.example.demo.dto.Author">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="address" property="address"></result>
<result column="phone" property="phone"></result>
<collection property="books" ofType="com.example.demo.dto.Book">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="press" property="press"></result>
<result column="price" property="price"></result>
<result column="author_id" property="authorId"></result>
</collection>
</resultMap>
<select id="queryAuthorInfo" parameterType="java.lang.String" resultMap="bookMap">
select t1.*,t2.* from
author t1 inner join book t2 on t1.id=t2.author_id
where t1.id=#{id}
</select>
使用postman执行查看结果：
{
"code": "200",
"msg": "成功",
"data": {
"id": 1,
"name": "法外狂徒张三",
"phone": null,
"address": null,
"books": [
{
"id": 1,
"name": "法外狂徒张三",
"press": "人民出版社",
"price": 10.00,
"authorId": 1
}
]
}
}
发现问题：本来author对应book有两条记录，结果books里面只返回了一条记录。
问题原因：2张表的主键都叫id，所以导致结果不能正确展示。
解决方法：1、主键使用不用的字段名。2、查询sql时使用别名
1、主键使用不用的字段名，涉及到更改数据库，只需要更改其中一个即可 。这里演示将book的id更改为book_id
<resultMap id="bookMap" type="com.example.demo.dto.Author">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="address" property="address"></result>
<result column="phone" property="phone"></result>
<collection property="books" ofType="com.example.demo.dto.Book">
<!---更改book类的id为bookId,数据库book的id更改为book_id-->
<id column="book_id" property="bookId"></id>
<result column="name" property="name"></result>
<result column="press" property="press"></result>
<result column="price" property="price"></result>
<result column="author_id" property="authorId"></result>
</collection>
</resultMap>
<select id="queryAuthorInfo" parameterType="java.lang.String" resultMap="bookMap">
select t1.*,t2.* from
author t1 inner join book t2 on t1.id=t2.author_id
where t1.id=#{id}
</select>
2、查询sql时使用别名。这里演示将查询book时id 更改别名为 bookId
<resultMap id="bookMap" type="com.example.demo.dto.Author">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="address" property="address"></result>
<result column="phone" property="phone"></result>
<collection property="books" ofType="com.example.demo.dto.Book">
<!---这里将column值id更改为别名一致bookId-->
<id column="bookId" property="id"></id>
<result column="name" property="name"></result>
<result column="press" property="press"></result>
<result column="price" property="price"></result>
<result column="author_id" property="authorId"></result>
</collection>
</resultMap>
<select id="queryAuthorInfo" parameterType="java.lang.String" resultMap="bookMap">
<!---这里新增了t2.id as bookId-->
select t1.*,t2.id as bookId, t2.* from
author t1 inner join book t2 on t1.id=t2.author_id
where t1.id=#{id}
</select>
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