MyBatis中怎么进行多对多关联查询

在MyBatis中进行多对多关联查询可以通过使用<collection>和<association>标签来实现。

假设有两个实体类Author和Book，它们之间是多对多的关系，一个作者可以写多本书，一本书也可以由多个作者共同写作。首先需要在Author和Book的Mapper文件中配置关联查询的SQL语句：

<!-- AuthorMapper.xml --><select id="getAuthorById" resultType="Author" parameterType="int">    SELECT * FROM author WHERE id = #{id}</select><select id="getBooksByAuthorId" resultType="Book" parameterType="int">    SELECT b.* FROM book b    JOIN author_book ab ON b.id = ab.book_id    WHERE ab.author_id = #{authorId}</select><!-- BookMapper.xml --><select id="getBookById" resultType="Book" parameterType="int">    SELECT * FROM book WHERE id = #{id}</select><select id="getAuthorsByBookId" resultType="Author" parameterType="int">    SELECT a.* FROM author a    JOIN author_book ab ON a.id = ab.author_id    WHERE ab.book_id = #{bookId}</select>

然后在Author和Book实体类中定义关联的属性：

public class Author {    private Integer id;    private String name;    private List<Book> books;        // 省略getter和setter方法}public class Book {    private Integer id;    private String title;    private List<Author> authors;        // 省略getter和setter方法}

最后在MyBatis配置文件中配置关联查询的映射：

<!-- AuthorMapper.xml --><resultMap id="AuthorResultMap" type="Author">    <id property="id" column="id" />    <result property="name" column="name" />    <collection property="books" ofType="Book" resultMap="BookResultMap" /></resultMap><!-- BookMapper.xml --><resultMap id="BookResultMap" type="Book">    <id property="id" column="id" />    <result property="title" column="title" />    <collection property="authors" ofType="Author" resultMap="AuthorResultMap" /></resultMap>

通过以上配置，就可以在AuthorMapper和BookMapper中查询到多对多关联的数据，并且在返回结果中包含关联的实体对象列表。