MyBatis中的ResultMap的association和collection标签详解

<resultMap  id="UsersMap" type="com.wang.test.demo.entity.User">
    <id property="id" column="id" jdbcType="INTEGER"/>
    <result property="username" column="username" jdbcType="VARCHAR"/>
    <result property="password" column="password" jdbcType="VARCHAR"/>
    <result property="role" column="role" jdbcType="VARCHAR"/>
    <result property="addTime" column="add_time" jdbcType="TIMESTAMP"/>
</resultMap>

@Data
//书籍
public class Book {
    private String id;
    private String name;
    private String author;
    private Double price;
    private Integer del;
    private Date publishdate;
    private String info;
    //把出版社对象当作属性
    private Publisher pub;//------重点在这里一本书对应一个出版社,这是一个出版社对象
}

@Data
//出版社
public class Publisher {
    private String id;
    private String name;
    private String phone;
    private String address;
}

<resultMap id="rMap_book" type="com.wang.test.demo.entity.Book">
	<!-- 主键  property为实体类属性 column为数据库字段 jdbcType为实体类对应的jdbc类型-->
    <id property="id" column="b_id" jdbcType="VARCHAR"></id>
    <!-- 普通属性  property为实体类属性 column为数据库字段  jdbcType为实体类对应的jdbc类型-->
    <result property="name" column="b_name" jdbcType="VARCHAR"></result>
    <result property="author" column="author" jdbcType="VARCHAR"></result>
    <result property="price" column="price" jdbcType="VARCHAR"></result>
    <result property="del" column="del" jdbcType="NUMERIC"></result>
    <result property="publisherid" column="publisher_id" jdbcType="VARCHAR"></result>
    <result property="publishdate" column="publish_date" jdbcType="TIMESTAMP"></result>
    <!--一对一映射association property 为实体类book中的属性名字 javaType为实体类属性的类型 -->
    <association property="pub" javaType="com.wang.test.demo.entity.Publisher">
        <id property="id" column="p_id" jdbcType="VARCHAR"></id>
        <result property="name" column="name" jdbcType="VARCHAR"></result>
        <result property="phone" column="phone" jdbcType="VARCHAR"></result>
        <result property="address" column="address" jdbcType="VARCHAR"></result>
    </association>
</resultMap>

@Data
//班级类
public class Class {

    private String id;
    private String name;
    private List<Student> students;//----重点在这里,一个班级对应多个学生

}

@Data
public class Student {

    private int id;
    private String name;
    private int age;
}

<resultMap id="rMap_class" type="com.wang.test.demo.entity.Class">
    <id property="id" column="id" jdbcType="VARCHAR"></id>
    <result property="name" column="name" jdbcType="VARCHAR"></result>
    <!--一对多映射用这个  ofTyp是一对多的集合的所存放的实体类  javaType实体类的属性类型-->
    <collection property="students" ofType="com.wang.test.demo.entity.Student" javaType="list">
        <id property="id" column="id" jdbcType="INTEGER"></id>
        <result property="name" column="name" jdbcType="VARCHAR"></result>
        <result property="age" column="age" jdbcType="INTEGER"></result>
    </collection>
</resultMap>