一对多关联关系
<?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="com.hous.day5.classMapper"> <!-- 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,student WHERE class.c_id=student.class_id AND class.c_id=#{id} SELECT * FROM class,student,teacher WHERE class.c_id=student.class_id AND class.teacher_id=teacher.t_id AND class.c_id=1 注意:映射关系要按照顺序,和javabean的属性对应 --> <select id="getClass" parameterType="int" resultMap="classResultMap"> SELECT * FROM class,student,teacher WHERE class.c_id=student.class_id AND class.teacher_id=teacher.t_id AND class.c_id=#{id} </select> <resultMap type="com.hous.day5.Classes" id="classResultMap"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" javaType="com.hous.day5.Teacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> <collection property="students" ofType="com.hous.day5.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="getClass2" parameterType="int" resultMap="classResultMap2"> SELECT * FROM class WHERE c_id=#{id} </select> <select id="getTeacher" parameterType="int" resultType="com.hous.day5.Teacher"> SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} </select> <select id="getStudents" parameterType="int" resultType="com.hous.day5.Student"> SELECT s_id id, s_name name FROM student WHERE class_id=1 </select> <resultMap type="com.hous.day5.Classes" id="classResultMap2"> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" column="teacher_id" select="getTeacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> <collection property="students" column="c_id" select="getStudents"> <id property="id" column="s_id"/> <result property="name" column="s_name"/> </collection> </resultMap> </mapper>
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/> <property name="username" value="root" /> <property name="password" value="root" /> </dataSource> </environment> </environments> <mappers> <mapper resource="com/hous/day5/classMapper.xml" /> </mappers> </configuration>
package com.hous.day5; import static org.junit.Assert.*; import java.io.InputStream; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Before; import org.junit.Test; public class MyTest { private SqlSessionFactory factory = null; @Before public void setUp() throws Exception { String resource = "day5/config.xml"; InputStream config = MyTest.class.getClassLoader().getResourceAsStream(resource); factory = new SqlSessionFactoryBuilder().build(config); } @Test public void testGetClass() { SqlSession session = factory.openSession(); String statement = "com.hous.day5.classMapper.getClass2"; Classes classes = session.selectOne(statement, 1); session.commit(); session.close(); System.out.println("查询结果:" + classes); } }
package com.hous.day5; import java.util.List; public class Classes { private int id; private String name; private Teacher teacher; private List<Student> students; public Classes() { super(); } public Classes(int id, String name, Teacher teacher) { super(); this.id = id; this.name = name; this.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; } public List<Student> getStudents() { return students; } public void setStudents(List<Student> students) { this.students = students; } /* (non-Javadoc) * @see java.lang.Object#toString() */ @Override public String toString() { return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + ", students=" + students + "]"; } }
package com.hous.day5; public class Student { private int id; private String 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 + "]"; } }
package com.hous.day5; public class Teacher { private int id; private String 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 + "]"; } }
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('xs_A',1),('xs_B',1),('xs_C',1),('xs_D',2),('xs_E',2),('xs_F',2);