【MyBatis】MyBatis之collection

MyBatis之collection

標簽的用法，與 相同，只是新增 ofType屬性，它用來將 JavaBean（或字段）屬性的類型和集合存儲的類型區分開來。

Book表數據

id	author_id	book_name
1	1	三國
2	1	水滸
3	2	紅樓

Author表數據

id	username	password	email	bio
1	張三	1	1	2
2	李四	1	1	1

@Data
public class Book {

	private Integer id;

	private Integer authorId;

	private String bookName;
}

@Data
public class Author {

	private Integer id;

	private String username;

	private String password;

	private String bio;

	private String email;
	
	private List<Book> books;
}

集合的嵌套結果映射

<select id="selectAuthor" resultMap="authorResultMap" >
    select 
    a.id,a.username,a.password,email,a.bio,
    b.id as book_id,b.author_id,b.book_name
    from author a left join book b 
    on a.id = b.author_id
</select>

	<resultMap id ="authorResultMap" type="Author">
		<id property="id" column="id"/>
		<result property="username" column="username"/>
		<result property="password" column="password	"/>
		<result property="email"    column="email"/>
		<result property="bio"      column="bio"/>
		<collection property="books" ofType="Book" column="author_id">
			<id property="id" column="book_id"/>
			<id property="authorId" column="author_id"/>
			<id property="bookName" column="book_name"/>
		</collection>
	</resultMap>

集合的嵌套 Select 查詢

<resultMap id ="authorResultMap2" type="Author">
		<id property="id" column="id"/>
		<result property="username" column="username"/>
		<result property="password" column="password	"/>
		<result property="email"    column="email"/>
		<result property="bio"      column="bio"/>
		<collection property="books" ofType="Book" select="selectBooks" column="{authorId=id}">
		</collection>
</resultMap>
<resultMap  id ="bookMap"         type="Book">
		<id     property="id"          column="id" />
		<result property="bookName"    column="book_name" />
		<result property="authorId"    column="author_id" />
</resultMap>
<select id ="selectBooks" resultMap="bookMap">
		select * from book where author_id = #{authorId}
	</select>
<select id="selectAuthor2" resultMap="authorResultMap2">
    select * from author
</select>

<!-- 前綴攔截-->
<resultMap id ="authorResultMap4" type="Author">
		<id property="id" column="id"/>
		<result property="username" column="username"/>
		<result property="password" column="password	"/>
		<result property="email"    column="email"/>
		<result property="bio"      column="bio"/>
		<collection property="books" ofType="Book"	resultMap="bookMap" columnPrefix="bk_" >
		</collection>
	</resultMap>
	
   <resultMap  id ="bookMap"         type="Book">
		<id     property="id"          column="id" />
		<result property="bookName"    column="book_name" />
		<result property="authorId"    column="author_id" />
	</resultMap>

代碼地址：https://gitee.com/firefish/mybatis_study

摘抄：https://mybatis.org/mybatis-3/zh/sqlmap-xml.html