Mybatis高级结果映射

有时侯，我们用SQL取得的结果需要映射到类似Map<key, Bean>这样的数据结构中或是映射到多个实体类中时，我们就需要使用到resultMap。下面用3个例子说明Mybatis高级结果映射的用法。

<环境准备>

请参照上一篇blog<Mybatis Guide>

<数据准备>

创建班级--学生表的一对多的数据结构

--创建班级表
CREATE TABLE tempdb..test_class
(
class_id int NOT NULL PRIMARY KEY,
class_name varchar(255),
class_admin_name varchar(255)
);
--创建学生表
CREATE TABLE tempdb..test_student
(
student_id int NOT NULL PRIMARY KEY,
class_id int,
student_name varchar(255),
student_age int,
student_address varchar(255)
);
--班级表中插入数据
insert tempdb..test_class values (101, 'Class 1, Grade 1', 'Mr. Zhang');
insert tempdb..test_class values (102, 'Class 2, Grade 1', 'Mr. Li');
insert tempdb..test_class values (103, 'Class 3, Grade 1', 'Mr. Wang');
insert tempdb..test_class values (201, 'Class 1, Grade 2', 'Mr. Zhao');
insert tempdb..test_class values (202, 'Class 2, Grade 2', 'Mr. Liu');
--学生表中插入数据
insert tempdb..test_student values (101001, 101, 'Name 1', 20, 'Address 1');
insert tempdb..test_student values (101002, 101, 'Name 2', 21, 'Address 2');
insert tempdb..test_student values (101003, 101, 'Name 3', 20, 'Address 3');
insert tempdb..test_student values (102001, 102, 'Name 4', 22, 'Address 4');
insert tempdb..test_student values (102002, 102, 'Name 5', 21, 'Address 5');
insert tempdb..test_student values (201001, 201, 'Name 6', 23, 'Address 6');
insert tempdb..test_student values (201002, 201, 'Name 7', 22, 'Address 7');
insert tempdb..test_student values (202001, 202, 'Name 8', 22, 'Address 8');

<创建实体类Entity>

package mybatistest;

import java.io.Serializable;

public class Clazz implements Serializable {

    private static final long serialVersionUID = 1L;

    private Integer classId;

    private String className;

    private String classAdminName;

    public Integer getClassId() {
        return classId;
    }

    public void setClassId(Integer classId) {
        this.classId = classId;
    }

    public String getClassName() {
        return className;
    }

    public void setClassName(String className) {
        this.className = className;
    }

    public String getClassAdminName() {
        return classAdminName;
    }

    public void setClassAdminName(String classAdminName) {
        this.classAdminName = classAdminName;
    }

    @Override
    public String toString() {
        return "Clazz [classId=" + classId + ", className=" + className + ", classAdminName=" + classAdminName + "]";
    }
}

package mybatistest;

import java.io.Serializable;

public class Student implements Serializable {

    private static final long serialVersionUID = 1L;

    private Integer studentId;

    private Integer classId;

    private String studentName;

    private Integer studentAge;

    private String studentAddress;

    public Integer getStudentId() {
        return studentId;
    }

    public void setStudentId(Integer studentId) {
        this.studentId = studentId;
    }

    public String getStudentName() {
        return studentName;
    }

    public Integer getClassId() {
        return classId;
    }

    public void setClassId(Integer classId) {
        this.classId = classId;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public Integer getStudentAge() {
        return studentAge;
    }

    public void setStudentAge(Integer studentAge) {
        this.studentAge = studentAge;
    }

    public String getStudentAddress() {
        return studentAddress;
    }

    public void setStudentAddress(String studentAddress) {
        this.studentAddress = studentAddress;
    }

    @Override
    public String toString() {
        return "Student [classId=" + classId + ", studentId=" + studentId + ", studentName=" + studentName
                + ", studentAge=" + studentAge + ", studentAddress=" + studentAddress + "]";
    }
}

<创建StudentsPerClass(OutputBean)>

创建一个Class的OutBean，其中包含classId，Class实体类，及Student实体类List以对应班级--学生的1对多关系。

package mybatistest;

import java.io.Serializable;
import java.util.List;

public class StudentsPerClass implements Serializable {

    private static final long serialVersionUID = 1L;

    private Integer classId;

    private Clazz clazz;

    private List<Student> students;

    public Integer getClassId() {
        return classId;
    }

    public void setClassId(Integer classId) {
        this.classId = classId;
    }

    public Clazz getClazz() {
        return clazz;
    }

    public void setClazz(Clazz clazz) {
        this.clazz = clazz;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(
                "StudentsPerClass [classId=" + classId + ", clazz=" + clazz + ", students=" + System.lineSeparator());
        students.forEach(p -> {
            sb.append("--").append(p).append(System.lineSeparator());
        });
        return sb.append("]").toString();
    }
}

<创建三个SQL实例>

(1) 用Map<学号, 学生实体类>映射一个学生集合

(2) 用List<StudentsPerClass>映射班级--学生的1对多关系

(3) 用Map<班级号, StudentsPerClass>映射班级--学生集合

ClassStudentRepository.java

package mybatistest;

import java.util.List;
import java.util.Map;

import org.apache.ibatis.annotations.MapKey;

public interface ClassStudentRepository {

    // 获取一个班级的所有学生[Map<[Student Id], [Student Info]>]
    @MapKey("studentId")
    Map<Integer, Student> getStudentsFromOneClass(Integer classId);

    // 获取一个年级的所有学生
    List<StudentsPerClass> getStudentsFromOneGrade(Integer gradeId);

    // 获取所有学生
    @MapKey("classId")
    Map<Integer, StudentsPerClass> getAllStudents();
}

ClassStudentRepository.xml

注意黄色部分非常重要，只有设置了1对多关系中的主键class_id，Mybatis才能自动映射这种1对多的嵌套关系。

<?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="mybatistest.ClassStudentRepository">
    <!-- // 获取一个班级的所有学生[Map<[Student Id], [Student Info]>] -->
    <select id="getStudentsFromOneClass" resultMap="studentsFromOneClassMap">
        SELECT
            t2.student_id,
            t2.class_id,
            t2.student_name,
            t2.student_age,
            t2.student_address
        FROM
            tempdb..test_class t1
        INNER JOIN
            tempdb..test_student t2
        ON
            t1.class_id = t2.class_id
        WHERE
            t1.class_id = #{classId} 
    </select>
    <resultMap id="studentsFromOneClassMap" type="mybatistest.Student">
        <id property="studentId" column="student_id" />
        <result property="classId" column="class_id" />
        <result property="studentName" column="student_name" />
        <result property="studentAge" column="student_age" />
        <result property="studentAddress" column="student_address" />
    </resultMap>

    <!-- 获取一个年级的所有学生 -->
    <select id="getStudentsFromOneGrade" resultMap="studentsFromOneGradeMap">
        SELECT
            t1.class_id,
            t1.class_name,
            t1.class_admin_name,
            t2.student_id,
            t2.student_name,
            t2.student_age,
            t2.student_address
        FROM
            tempdb..test_class t1
        INNER JOIN
            tempdb..test_student t2
        ON
            t1.class_id = t2.class_id
        WHERE
            t1.class_id/100 = #{gradeId} 
    </select>
    <resultMap id="studentsFromOneGradeMap" type="mybatistest.StudentsPerClass">
        <id property="classId" column="class_id"/>
        <association property="clazz" javaType="mybatistest.Clazz" >
            <id property="classId" column="class_id"/>
            <result property="className" column="class_name"/>
            <result property="classAdminName" column="class_admin_name"/>
        </association>
        <collection property="students" ofType="mybatistest.Student">
            <id property="studentId" column="student_id" />
            <result property="classId" column="class_id"/>
            <result property="studentName" column="student_name" />
            <result property="studentAge" column="student_age" />
            <result property="studentAddress" column="student_address" />
        </collection>
    </resultMap>

    <!-- 获取所有学生 -->
    <select id="getAllStudents" resultMap="allStudentsMap">
        SELECT
            t1.class_id,
            t1.class_name,
            t1.class_admin_name,
            t2.student_id,
            t2.student_name,
            t2.student_age,
            t2.student_address
        FROM
            tempdb..test_class t1
        INNER JOIN
            tempdb..test_student t2
        ON
            t1.class_id = t2.class_id
    </select>
    <resultMap id="allStudentsMap" type="mybatistest.StudentsPerClass">
        <id property="classId" column="class_id"/>
        <association property="clazz" javaType="mybatistest.Clazz" >
            <id property="classId" column="class_id"/>
            <result property="className" column="class_name"/>
            <result property="classAdminName" column="class_admin_name"/>
        </association>
        <collection property="students" ofType="mybatistest.Student">
            <id property="studentId" column="student_id" />
            <result property="classId" column="class_id"/>
            <result property="studentName" column="student_name" />
            <result property="studentAge" column="student_age" />
            <result property="studentAddress" column="student_address" />
        </collection>
    </resultMap>
</mapper>

mybatis-config.xml中添加映射关系

    <mappers>
        <mapper resource="mybatistest/ClassStudentRepository.xml" />
    </mappers>

<测试结果>

package mybatistest;

import java.util.List;
import java.util.Map;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

public class MainTest {

    public static void main(String[] args) {
        SqlSessionFactory sqlSessionFactory = MybatisTestSessionFactory.getSqlSessionFactoryInstance();
        SqlSession session = sqlSessionFactory.openSession();
        ClassStudentRepository classStudentRepository = session.getMapper(ClassStudentRepository.class);
        Map<Integer, Student> res1 = classStudentRepository.getStudentsFromOneClass(102);
        res1.forEach((p, q) -> {
            System.out.println("Student ID: " + p + "; Student info: " + q);
        });
        // [Output]
        // Student ID: 102001; Student info: Student [classId=102, studentId=102001, studentName=Name 4, studentAge=22, studentAddress=Address 4]
        // Student ID: 102002; Student info: Student [classId=102, studentId=102002, studentName=Name 5, studentAge=21, studentAddress=Address 5]
        List<StudentsPerClass> res2 = classStudentRepository.getStudentsFromOneGrade(1);
        res2.forEach((p) -> {
            System.out.println(p);
        });
        // [Output]
        // StudentsPerClass [classId=101, clazz=Clazz [classId=101, className=Class 1, Grade 1, classAdminName=Mr. Zhang], students=
        // --Student [classId=101, studentId=101001, studentName=Name 1, studentAge=20, studentAddress=Address 1]
        // --Student [classId=101, studentId=101002, studentName=Name 2, studentAge=21, studentAddress=Address 2]
        // --Student [classId=101, studentId=101003, studentName=Name 3, studentAge=20, studentAddress=Address 3]
        // ]
        // StudentsPerClass [classId=102, clazz=Clazz [classId=102, className=Class 2, Grade 1, classAdminName=Mr. Li], students=
        // --Student [classId=102, studentId=102001, studentName=Name 4, studentAge=22, studentAddress=Address 4]
        // --Student [classId=102, studentId=102002, studentName=Name 5, studentAge=21, studentAddress=Address 5]
        // ]
        Map<Integer, StudentsPerClass> res3 = classStudentRepository.getAllStudents();
        res3.forEach((p, q) -> {
            System.out.println("Class ID: " + p + System.lineSeparator() + q);
        });
        // [Output]
        // Class ID: 101
        // StudentsPerClass [classId=101, clazz=Clazz [classId=101, className=Class 1, Grade 1, classAdminName=Mr. Zhang], students=
        // --Student [classId=101, studentId=101001, studentName=Name 1, studentAge=20, studentAddress=Address 1]
        // --Student [classId=101, studentId=101002, studentName=Name 2, studentAge=21, studentAddress=Address 2]
        // --Student [classId=101, studentId=101003, studentName=Name 3, studentAge=20, studentAddress=Address 3]
        // ]
        // Class ID: 102
        // StudentsPerClass [classId=102, clazz=Clazz [classId=102, className=Class 2, Grade 1, classAdminName=Mr. Li], students=
        // --Student [classId=102, studentId=102001, studentName=Name 4, studentAge=22, studentAddress=Address 4]
        // --Student [classId=102, studentId=102002, studentName=Name 5, studentAge=21, studentAddress=Address 5]
        // ]
        // Class ID: 201
        // StudentsPerClass [classId=201, clazz=Clazz [classId=201, className=Class 1, Grade 2, classAdminName=Mr. Zhao], students=
        // --Student [classId=201, studentId=201001, studentName=Name 6, studentAge=23, studentAddress=Address 6]
        // --Student [classId=201, studentId=201002, studentName=Name 7, studentAge=22, studentAddress=Address 7]
        // ]
        // Class ID: 202
        // StudentsPerClass [classId=202, clazz=Clazz [classId=202, className=Class 2, Grade 2, classAdminName=Mr. Liu], students=
        // --Student [classId=202, studentId=202001, studentName=Name 8, studentAge=22, studentAddress=Address 8]
        // ]
        session.close();
    }
}