MyBatis一对一，一对多关于model和mapper.xml的编写

一直以来对这块都比较模糊，每次用都是自己百度过来，决定还是自己试一下，记录下来。

数据表：

student表：

class_info表：

一、先写个一对一的

Student.java模型

public class Student {
    private Integer id;

    private String name;

    private Integer age;

    private ClassInfo classInfo;

    public ClassInfo getClassInfo() {
		return classInfo;
	}

	public void setClassInfo(ClassInfo classInfo) {
		this.classInfo = classInfo;
	}

	public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name == null ? null : name.trim();
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ", age=" + age + ", classInfo=" + classInfo + "]";
	}
}

ClassInfo模型：

public class ClassInfo {
    private Integer id;

    private String classDesc;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getClassDesc() {
        return classDesc;
    }

    public void setClassDesc(String classDesc) {
        this.classDesc = classDesc == null ? null : classDesc.trim();
    }

	@Override
	public String toString() {
		return "ClassInfo [id=" + id + ", classDesc=" + classDesc + "]";
	}
}

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.sadoshi.SpringMyBatis.Mapper.StudentMapper">

	<!-- 方法一 -->
	<resultMap id="BaseResultMap1" type="com.sadoshi.SpringMyBatis.model.Student">
		<id column="id" jdbcType="INTEGER" property="id" />
		<result column="name" jdbcType="VARCHAR" property="name" />
		<result column="age" jdbcType="INTEGER" property="age" />
		<association property="classInfo" column="class_id"
			javaType="com.sadoshi.SpringMyBatis.model.ClassInfo">
			<id property="id" column="class_info_id" />
			<result property="classDesc" column="class_desc" />
		</association>
	</resultMap>

	<!-- 方法二 -->
	<resultMap id="BaseResultMap2" type="com.sadoshi.SpringMyBatis.model.Student">
		<id column="id" jdbcType="INTEGER" property="id" />
		<result column="name" jdbcType="VARCHAR" property="name" />
		<result column="age" jdbcType="INTEGER" property="age" />

		<result column="id" jdbcType="INTEGER" property="classInfo.id" />
		<result column="class_desc" jdbcType="VARCHAR" property="classInfo.classDesc" />
	</resultMap>

	<!-- 方法三 -->
	<resultMap id="classinfoResult" type="com.sadoshi.SpringMyBatis.model.ClassInfo">
		<result column="id" jdbcType="INTEGER" property="id" />
		<result column="class_desc" jdbcType="VARCHAR" property="classDesc" />
	</resultMap>
	<resultMap id="BaseResultMap3" type="com.sadoshi.SpringMyBatis.model.Student">
		<id column="id" jdbcType="INTEGER" property="id" />
		<result column="name" jdbcType="VARCHAR" property="name" />
		<result column="age" jdbcType="INTEGER" property="age" />
		<association property="classInfo" resultMap="classinfoResult" />
	</resultMap>

	<!-- 方法四 -->
	<resultMap id="BaseResultMap4" type="com.sadoshi.SpringMyBatis.model.Student">
		<id column="id" jdbcType="INTEGER" property="id" />
		<result column="name" jdbcType="VARCHAR" property="name" />
		<result column="age" jdbcType="INTEGER" property="age" />
		<association property="classInfo" column="class_id"
			select="com.sadoshi.SpringMyBatis.Mapper.ClassInfoMapper.selectByPrimaryKey" />
	</resultMap>

	<!-- 方法一 -->
	<select id="selectByPrimaryKey1" parameterType="java.lang.Integer"
		resultMap="BaseResultMap1">
		select a.id, a.name, a.age, b.id class_info_id, class_desc
		from student a,class_info b
		where a.id = #{id,jdbcType=INTEGER} and a.class_id=b.id
	</select>

	<!-- 方法二 -->
	<select id="selectByPrimaryKey2" parameterType="java.lang.Integer"
		resultMap="BaseResultMap2">
		select a.id, a.name, a.age, b.id classinfo_id, class_desc
		from student a,class_info b
		where a.id = #{id,jdbcType=INTEGER} and a.class_id=b.id
	</select>

	<!-- 方法三 -->
	<select id="selectByPrimaryKey3" parameterType="java.lang.Integer"
		resultMap="BaseResultMap3">
		select a.id, a.name, a.age, b.id classinfo_id, class_desc
		from student a,class_info b
		where a.id = #{id,jdbcType=INTEGER} and a.class_id=b.id
	</select>
	
	<!-- 方法四 -->
    <select id="selectByPrimaryKey4" parameterType="java.lang.Integer"
        resultMap="BaseResultMap4">
        select id, name, age, class_id
        from student
        where id = #{id,jdbcType=INTEGER}
    </select>
</mapper>

ClassInfoMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.sadoshi.SpringMyBatis.Mapper.ClassInfoMapper">
  <resultMap id="BaseResultMap" type="com.sadoshi.SpringMyBatis.model.ClassInfo">
    <id column="id" jdbcType="INTEGER" property="id" />
    <result column="class_desc" jdbcType="VARCHAR" property="classDesc" />
  </resultMap>
  <sql id="Base_Column_List">
    id, class_desc
  </sql>
  <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from class_info
    where id = #{id,jdbcType=INTEGER}
  </select>
</mapper>

总结了一下，xml有四种方法实现一对一，主要是ResultMap的不同写法写法，Select语句是一样的。据说通常开发用方法四比较多。