Mybatis连接查询返回类型问题

一对一映射

public class Card {
	private Integer id;
	private String num;
	private Student student; //重要
	public Card(){}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getNum() {
		return num;
	}
	public void setNum(String num) {
		this.num = num;
	}
	public Student getStudent() {
		return student;
	}
	public void setStudent(Student student) {
		this.student = student;
	}
}
public class Student {
	private Integer id;
	private String name;
	private Card card; //重要
	public Student(){}
	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;
	}
	public Card getCard() {
		return card;
	}
	public void setCard(Card card) {
		this.card = card;
	}
}

　映射文件

CardMapper.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="cardNamespace">
	<resultMap type="cn.itcast.javaee.mybatis.one2one.Card" id="cardMap">
		<id property="id" column="id" />
		<result property="num" column="num" />
	</resultMap>
</mapper>

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="studentNamespace">
	<resultMap type="cn.itcast.javaee.mybatis.one2one.Student" id="studentMap">
		<id property="id" column="id" />
		<result property="name" column="name"/>
		<association property="card" resultMap="cardNamespace.cardMap"/>
	</resultMap>
	<select id="findById" parameterType="int" resultMap="studentMap">
		select s.id,s.name,c.id,c.num
		from students s inner join cards c
		on s.cid = c.id
		and s.id = #{id}
	</select>
</mapper>

一对多映射

/**
 * 班级（单方）
 * @author AdminTC
 */
public class Grade {
	private Integer id;
	private String name;
	private List<Student> studentList = new ArrayList<Student>();
	public Grade(){}
	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;
	}
	public List<Student> getStudentList() {
		return studentList;
	}
	public void setStudentList(List<Student> studentList) {
		this.studentList = studentList;
	}
}
/**
 * 学生（多方）
 * @author AdminTC
 */
public class Student {
	private Integer id;
	private String name;
	private Grade grade;
	public Student(){}
	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;
	}
	public Grade getGrade() {
		return grade;
	}
	public void setGrade(Grade grade) {
		this.grade = grade;
	}
}

　　映射文件

GradeMapper.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="gradeNamespace">
	<resultMap type="cn.itcast.javaee.mybatis.one2many.Grade" id="gradeMap">
		<id property="id" column="gid" />
		<result property="name" column="gname"/>
		<collection property="studentList" resultMap="studentNamespace.studentMap"/>
	</resultMap>
	<select id="findGradeByName" parameterType="string" resultMap="gradeMap">
		select g.gid,g.gname,s.sid,s.sname
		from grades g,students s
		where g.gid = s.sgid
		and s.sname = #{name}
	</select>
</mapper>

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="studentNamespace">
	<resultMap type="cn.itcast.javaee.mybatis.one2many.Student" id="studentMap">
		<id property="id" column="sid" />
		<result property="name" column="sname"/>
		<association property="grade" resultMap="gradeNamespace.gradeMap"/>
	</resultMap>
	<select id="findAllByName" parameterType="string" resultMap="studentMap">
		select s.sid,s.sname,g.gid,g.gname
		from grades g,students s
		where g.gid = s.sgid
		and g.gname = #{name}
	</select>
</mapper>

多对多映射

/**
 * 学生(多方)
 * @author AdminTC
 */
public class Student {
	private Integer id;
	private String name;
	private List<Course> courseList = new ArrayList<Course>();
	public Student(){}
	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;
	}
	public List<Course> getCourseList() {
		return courseList;
	}
	public void setCourseList(List<Course> courseList) {
		this.courseList = courseList;
	}
}
/**
 * 课程(多方)
 * @author AdminTC
 */
public class Course {
	private Integer id;
	private String name;
	private List<Student> studentList = new ArrayList<Student>();
	public Course(){}
	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;
	}
	public List<Student> getStudentList() {
		return studentList;
	}
	public void setStudentList(List<Student> studentList) {
		this.studentList = studentList;
	}
}

　　映射文件

  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="studentNamespace">
	<resultMap type="cn.itcast.javaee.mybatis.many2many.Student" id="studentMap">
		<id property="id" column="sid" />
		<result property="name" column="sname"/>
	</resultMap>
	<select id="findStudentByName" parameterType="string" resultMap="studentMap">
		select s.sid,s.sname
		from students s,middles m,courses c
		where s.sid = m.sid
		and m.cid = c.cid
		and c.cname = #{name}
	</select>
</mapper>
   CourseMapper.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="courseNamespace">
	<resultMap type="cn.itcast.javaee.mybatis.many2many.Course" id="courseMap">
		<id property="id" column="cid" />
		<result property="name" column="cname"/>
	</resultMap>
	<select id="findCourseByName" parameterType="string" resultMap="courseMap">
		select c.cid,c.cname
		from students s,middles m,courses c
		where s.sid = m.sid
		and m.cid = c.cid
		and s.sname = #{name}
	</select>
</mapper>