标签:实现 add 老师 cti 字段 oct sys map 标签
1.一对一关联
1.1根据班级id查询班级信息,并且查询出老师的信息
1.2 创建表和数据
创建老师表和学生表,假设一个老师只负责一个班级,这样就可以实现一对一关系
CREATE TABLE teacher( t_id INT PRIMARY KEY AUTO_INCREMENT, t_name VARCHAR(20) ); CREATE TABLE class( c_id INT PRIMARY KEY AUTO_INCREMENT, c_name VARCHAR(20), teacher_id INT ); ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id); INSERT INTO teacher(t_name) VALUES(‘teacher1‘); INSERT INTO teacher(t_name) VALUES(‘teacher2‘); INSERT INTO class(c_name, teacher_id) VALUES(‘class_a‘, 1); INSERT INTO class(c_name, teacher_id) VALUES(‘class_b‘, 2);
表之间的关系如下:
1.4 创建实体类
1)teacher类
package me.gacl.domain; /** * @author gacl * 定义teacher表对应的实体类 */ public class Teacher { //定义实体类的属性,与teacher表中的字段对应 private int id; //id===>t_id private String name; //name===>t_name public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Teacher [id=" + id + ", name=" + name + "]"; } }
2)classes 类
package me.gacl.domain; /** * @author gacl * 定义class表对应的实体类 */ public class Classes { //定义实体类的属性,与class表中的字段对应 private int id; //id===>c_id private String name; //name===>c_name /** * class表中有一个teacher_id字段,所以在Classes类中定义一个teacher属性, * 用于维护teacher和class之间的一对一关系,通过这个teacher属性就可以知道这个班级是由哪个老师负责的 */ private Teacher teacher; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } @Override public String toString() { return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher+ "]"; } }
1.5 定义sql映射文件
<?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"> <!-- 为这个mapper指定一个唯一的namespace,namespace的值习惯上设置成包名+sql映射文件名,这样就能够保证namespace的值是唯一的 例如namespace="me.gacl.mapping.classMapper"就是me.gacl.mapping(包名)+classMapper(classMapper.xml文件去除后缀) --> <mapper namespace="me.gacl.mapping.classMapper"> <!-- 根据班级id查询班级信息(带老师的信息) ##1. 联表查询 SELECT * FROM class c,teacher t WHERE c.teacher_id=t.t_id AND c.c_id=1; ##2. 执行两次查询 SELECT * FROM class WHERE c_id=1; //teacher_id=1 SELECT * FROM teacher WHERE t_id=1;//使用上面得到的teacher_id --> <!-- 方式一:嵌套结果:使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1 --> <select id="getClass" parameterType="int" resultMap="ClassResultMap"> select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id} </select> <!-- 使用resultMap映射实体类和字段之间的一一对应关系 --> <resultMap type="me.gacl.domain.Classes" id="ClassResultMap"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" javaType="me.gacl.domain.Teacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> </resultMap> <!-- 方式二:嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1; SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值 --> <select id="getClass2" parameterType="int" resultMap="ClassResultMap2"> select * from class where c_id=#{id} </select> <!-- 使用resultMap映射实体类和字段之间的一一对应关系 --> <resultMap type="me.gacl.domain.Classes" id="ClassResultMap2"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" column="teacher_id" select="getTeacher"/> </resultMap> <select id="getTeacher" parameterType="int" resultType="me.gacl.domain.Teacher"> SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} </select> </mapper>
1.6 编写测试类
package me.gacl.test; import me.gacl.domain.Classes; import me.gacl.util.MyBatisUtil; import org.apache.ibatis.session.SqlSession; import org.junit.Test; public class Test3 { @Test public void testGetClass(){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); /** * 映射sql的标识字符串, * me.gacl.mapping.classMapper是classMapper.xml文件中mapper标签的namespace属性的值, * getClass是select标签的id属性值,通过select标签的id属性值就可以找到要执行的SQL */ String statement = "me.gacl.mapping.classMapper.getClass";//映射sql的标识字符串 //执行查询操作,将查询结果自动封装成Classes对象返回 Classes clazz = sqlSession.selectOne(statement,1);//查询class表中id为1的记录 //使用SqlSession执行完SQL之后需要关闭SqlSession sqlSession.close(); System.out.println(clazz);//打印结果:Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1]] } @Test public void testGetClass2(){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); /** * 映射sql的标识字符串, * me.gacl.mapping.classMapper是classMapper.xml文件中mapper标签的namespace属性的值, * getClass2是select标签的id属性值,通过select标签的id属性值就可以找到要执行的SQL */ String statement = "me.gacl.mapping.classMapper.getClass2";//映射sql的标识字符串 //执行查询操作,将查询结果自动封装成Classes对象返回 Classes clazz = sqlSession.selectOne(statement,1);//查询class表中id为1的记录 //使用SqlSession执行完SQL之后需要关闭SqlSession sqlSession.close(); System.out.println(clazz);//打印结果:Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1]] } }
1.7 Mybatis一对一关联查询总结
1)Mybatis使用 association 来解决一对一关联查询,association标签可用的属性:
* property:对象属性的名称
* javaType:对象属性的类型
* column : 所对应的外键的字段名称
* select : 使用另一个查询封装的结果
2.一对多关联查询
2.1 根据classId查询对应的班级信息,包括老师和学生
2.2 创建表和数据
CREATE TABLE student( s_id INT PRIMARY KEY AUTO_INCREMENT, s_name VARCHAR(20), class_id INT ); INSERT INTO student(s_name, class_id) VALUES(‘student_A‘, 1); INSERT INTO student(s_name, class_id) VALUES(‘student_B‘, 1); INSERT INTO student(s_name, class_id) VALUES(‘student_C‘, 1); INSERT INTO student(s_name, class_id) VALUES(‘student_D‘, 2); INSERT INTO student(s_name, class_id) VALUES(‘student_E‘, 2); INSERT INTO student(s_name, class_id) VALUES(‘student_F‘, 2);
2.3 定义实体类
(1)student类
package me.gacl.domain; /** * @author gacl * 定义student表所对应的实体类 */ public class Student { //定义属性,和student表中的字段对应 private int id; //id===>s_id private String name; //name===>s_name public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Student [id=" + id + ", name=" + name + "]"; } }
(2) 修改classes类,添加一个List<Student> students属性,使用一个List<Student> 来表示班级所拥有的学生(即在一的一方植入多的一方的属性)
package me.gacl.domain; import java.util.List; /** * @author gacl * 定义class表对应的实体类 */ public class Classes { //定义实体类的属性,与class表中的字段对应 private int id; //id===>c_id private String name; //name===>c_name /** * class表中有一个teacher_id字段,所以在Classes类中定义一个teacher属性, * 用于维护teacher和class之间的一对一关系,通过这个teacher属性就可以知道这个班级是由哪个老师负责的 */ private Teacher teacher; //使用一个List<Student>集合属性表示班级拥有的学生 private List<Student> students; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } public List<Student> getStudents() { return students; } public void setStudents(List<Student> students) { this.students = students; } @Override public String toString() { return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + ", students=" + students + "]"; } }
2.4 修改sql映射文件
<!-- 根据classId查询对应的班级信息,包括学生,老师 --> <!-- 方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集 SELECT * FROM class c, teacher t,student s WHERE c.teacher_id=t.t_id AND c.C_id=s.class_id AND c.c_id=1 --> <select id="getClass3" parameterType="int" resultMap="ClassResultMap3"> select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.C_id=s.class_id and c.c_id=#{id} </select> <resultMap type="me.gacl.domain.Classes" id="ClassResultMap3"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" column="teacher_id" javaType="me.gacl.domain.Teacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> <!-- ofType指定students集合中的对象类型 --> <collection property="students" ofType="me.gacl.domain.Student"> <id property="id" column="s_id"/> <result property="name" column="s_name"/> </collection> </resultMap> <!-- 方式二:嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1; SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值 SELECT * FROM student WHERE class_id=1 //1是第一个查询得到的c_id字段的值 --> <select id="getClass4" parameterType="int" resultMap="ClassResultMap4"> select * from class where c_id=#{id} </select> <resultMap type="me.gacl.domain.Classes" id="ClassResultMap4"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" column="teacher_id" javaType="me.gacl.domain.Teacher" select="getTeacher2"></association> <collection property="students" ofType="me.gacl.domain.Student" column="c_id" select="getStudent"></collection> </resultMap> <select id="getTeacher2" parameterType="int" resultType="me.gacl.domain.Teacher"> SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} </select> <select id="getStudent" parameterType="int" resultType="me.gacl.domain.Student"> SELECT s_id id, s_name name FROM student WHERE class_id=#{id} </select>
2.5 编写测试方法
package me.gacl.test; import me.gacl.domain.Classes; import me.gacl.util.MyBatisUtil; import org.apache.ibatis.session.SqlSession; import org.junit.Test; public class Test4 { @T public void testGetClass3(){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); /** * 映射sql的标识字符串, * me.gacl.mapping.classMapper是classMapper.xml文件中mapper标签的namespace属性的值, * getClass3是select标签的id属性值,通过select标签的id属性值就可以找到要执行的SQL */ String statement = "me.gacl.mapping.classMapper.getClass3";//映射sql的标识字符串 //执行查询操作,将查询结果自动封装成Classes对象返回 Classes clazz = sqlSession.selectOne(statement,1);//查询class表中id为1的记录 //使用SqlSession执行完SQL之后需要关闭SqlSession sqlSession.close(); //打印结果:Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1], students=[Student [id=1, name=student_A], Student [id=2, name=student_B], Student [id=3, name=student_C]]] System.out.println(clazz); } @Test public void testGetClass4(){ SqlSession sqlSession = MyBatisUtil.getSqlSession(); /** * 映射sql的标识字符串, * me.gacl.mapping.classMapper是classMapper.xml文件中mapper标签的namespace属性的值, * getClass4是select标签的id属性值,通过select标签的id属性值就可以找到要执行的SQL */ String statement = "me.gacl.mapping.classMapper.getClass4";//映射sql的标识字符串 //执行查询操作,将查询结果自动封装成Classes对象返回 Classes clazz = sqlSession.selectOne(statement,1);//查询class表中id为1的记录 //使用SqlSession执行完SQL之后需要关闭SqlSession sqlSession.close(); //打印结果:Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1], students=[Student [id=1, name=student_A], Student [id=2, name=student_B], Student [id=3, name=student_C]]] System.out.println(clazz); } }
2.6 Mybatis中使用collection来解决一对多的关联查询,ofType属性指定集合中元素的对象类型。
标签:实现 add 老师 cti 字段 oct sys map 标签
原文地址:http://www.cnblogs.com/cn-930621/p/7577287.html