MyBatis3注解的关系映射

1. MyBatis3注解的关系映射
   

1) 一对一映射；
2) 一对多映射；

package com.andrew.mappers;
import org.apache.ibatis.annotations.Select;
import com.andrew.model.Address;
public interface AddressMapper {
    @Select("select * from t_address where id=#{id}")
    public Address findById(Integer id);
}

package com.andrew.mappers;
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import com.andrew.model.Grade;
public interface GradeMapper {
    @Select("select * from t_grade where id=#{id}")
    @Results({
        @Result(id=true,column="id",property="id"),
        @Result(column="gradeName",property="gradeName"),
    @Result(column="id",property="students",many=@Many(select="com.andrew.mappers.StudentMapper.selectStudentByGradeId"))
    })
    public Grade findById(Integer id);
}

package com.andrew.mappers;
import java.util.List;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
import com.andrew.model.Student;
public interface StudentMapper {
    @Insert("insert into t_student values(null,#{name},#{age},1,1,1,1)")
    public int insertStudent(Student student);
    @Update("update t_student set name=#{name},age=#{age} where id=#{id}")
    public int updateStudent(Student student);
    @Delete("delete from t_student where id=#{id}")
    public int deleteStudent(int id);
    @Select("select * from t_student where id=#{id}")
    public Student getStudentById(Integer id);
    @Select("select * from t_student")
    @Results({
        @Result(id=true,column="id",property="id"),
        @Result(column="name",property="name"),
        @Result(column="age",property="age")
    })
    public List<Student> findStudents();
    @Select("select * from t_student where id=#{id}")
    @Results({
        @Result(id=true,column="id",property="id"),
        @Result(column="name",property="name"),
        @Result(column="age",property="age"),
    @Result(column="addressId",property="address",one=@One(select="com.andrew.mappers.AddressMapper.findById"))
    })
    public Student selectStudentWithAddress(int id);
    @Select("select * from t_student where gradeId=#{gradeId}")
    @Results({
        @Result(id=true,column="id",property="id"),
        @Result(column="name",property="name"),
        @Result(column="age",property="age"),
    @Result(column="addressId",property="address",one=@One(select="com.andrew.mappers.AddressMapper.findById"))
    })
    public Student selectStudentByGradeId(int gradeId);
    @Select("select * from t_student where id=#{id}")
    @Results({
        @Result(id=true,column="id",property="id"),
        @Result(column="name",property="name"),
        @Result(column="age",property="age"),
    @Result(column="addressId",property="address",one=@One(select="com.andrew.mappers.AddressMapper.findById")),
        @Result(column="gradeId",property="grade",one=@One(select="com.andrew.mappers.GradeMapper.findById"))
    })
    public Student selectStudentWithAddressAndGrade(int id);
}

package com.andrew.model;
public class Address {
    private Integer id;
    private String sheng;
    private String shi;
    private String qu;
    @Override
    public String toString() {
        return "Address [id=" + id + ", sheng=" + sheng + ", shi=" + shi
                + ", qu=" + qu + "]";
    }
    // getter and setter
}

package com.andrew.model;
import java.util.List;
public class Grade {
    private Integer id;
    private String gradeName;
    private List<Student> students;
    @Override
    public String toString() {
        return "Grade [id=" + id + ", gradeName=" + gradeName + "]";
    }
    // getter and setter
}

package com.andrew.model;
public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private Address address;
    private Grade grade;
    public Student() {
        super();
    }
    public Student(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }
    public Student(Integer id, String name, Integer age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", age=" + age
                + ", address=" + address + ", grade=" + grade + "]";
    }
    // getter and setter
}

package com.andrew.service;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.andrew.mappers.GradeMapper;
import com.andrew.mappers.StudentMapper;
import com.andrew.model.Grade;
import com.andrew.model.Student;
import com.andrew.util.SqlSessionFactoryUtil;
public class StudentGradeTest {
    private SqlSession sqlSession = null;
    private StudentMapper studentMapper = null;
    private GradeMapper gradeMapper = null;
    @Before
    public void setUp() throws Exception {
        sqlSession = SqlSessionFactoryUtil.openSession();
        studentMapper = sqlSession.getMapper(StudentMapper.class);
        gradeMapper = sqlSession.getMapper(GradeMapper.class);
    }
    @After
    public void tearDown() throws Exception {
        sqlSession.close();
    }
    @Test
    public void testSelectStudentWithAddress() {
        Student student = studentMapper.selectStudentWithAddress(2);
        System.out.println(student);
    }
    @Test
    public void testSelectGradeWithStudents() {
        Grade grade = gradeMapper.findById(2);
        System.out.println(grade);
        List<Student> studentList = grade.getStudents();
        for (Student student : studentList) {
            System.out.println(student);
        }
    }
    @Test
    public void testSelectStudentWithAddressAndGrade() {
        Student student = studentMapper.selectStudentWithAddressAndGrade(1);
        System.out.println(student);
    }
}