本篇内容介绍了“怎么解决mybatis一对多查询resultMap只返回了一条记录问题”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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
@Datapublic class Author { private Integer id; private String name; private String phone; private String address; private List<Book> books;}@Datapublic 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>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>“怎么解决mybatis一对多查询resultMap只返回了一条记录问题”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注编程网网站，小编将为大家输出更多高质量的实用文章！
