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Mybatis复杂查询的实现

作者：雪顶猫的鳄

本文主要介绍了Mybatis复杂查询的实现,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友们下面随着小编来一起学习学习吧

一、环境搭建

1.1 建表

CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO teacher(`id`, `name`) VALUES (1, '乔丹'); 
INSERT INTO teacher(`id`, `name`) VALUES (2, '科比'); 
INSERT INTO teacher(`id`, `name`) VALUES (1, '垫脚哥'); 

CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8

INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '杜兰特', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '德罗赞', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '詹姆斯', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '卡子哥', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '乔治', '1');

1.2 导入依赖

<dependencies>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.16</version>
    </dependency>
	<dependency>
	    <groupId>org.mybatis</groupId>
	    <artifactId>mybatis</artifactId>
	    <version>3.5.2</version>
	</dependency>
	<dependency>
	    <groupId>mysql</groupId>
	    <artifactId>mysql-connector-java</artifactId>
	    <version>5.1.47</version>
	</dependency>
	<dependency>
	    <groupId>junit</groupId>
	    <artifactId>junit</artifactId>
	    <version>4.12</version>
	</dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.12</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

1.3 创建实体类

1.3.1 Student 实体类

@Data
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    //学生要关联一个老师
    private Teacher teacher;
    }

1.3.2 Teacher 实体类

@Data
public class Teacher {
    private int id;
    private String name;
    }

1.4 创建Mapper接口

1.4.1 StudentMapper 接口

public interface StudentMapper {
}

1.4.2 TeacherMapper 接口

public interface TeacherMapper {
    @Select("select *from teacher where id=#{tid}")
    Teacher getTeacher(@Param("tid") int id);
    }

1.5 创建Mapper.xml文件

1.5.1 namespace 绑定StudentMapper接口

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.kuang.dao.StudentMapper">

</mapper>

1.5.2 namespace 绑定TeacherMapper接口

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"        "http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.kuang.dao.TeacherMapper">   </mapper>

1.6 核心配置文件中注册Mapper.xml文件

<?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>

    <properties resource="db.properties"/>
    <settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <typeAliases>
       <package name="com.kuang.pojo"/>
       <!-- <typeAlias type="com.kuang.pojo.User" alias="User"/>-->
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper class="com.kuang.dao.TeacherMapper"/>
        <mapper class="com.kuang.dao.StudentMapper"/>
    </mappers>

</configuration>

1.7 测试

@Test
public void getTeacher(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();    TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
    Teacher teacher = mapper.getTeacher(1);    
    System.out.println(teacher);    
    sqlSession.close();
    }

测试结果

在这里插入图片描述

二、多对一复杂查询

2.1 按照查询嵌套处理

2.1.1 编写接口方法

public interface StudentMapper {
 //查询所有的学生信息，以及对应的老师信息 
 List<Student> getStudent();
 }

2.1.2 编写sql标签

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"        
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.kuang.dao.StudentMapper">   
         <select id="getStudent" resultMap="StudentTeacher">
             select *from student;
         </select>
         <resultMap id="StudentTeacher" type="Student">
             <result property="id" column="id"/>
             <result property="name" column="name"/>
             <!--复杂的属性：我们要单独处理 对象：association 集合：collection -->        
             <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>   
         </resultMap>
         <select id="getTeacher" resultType="Teacher" >
             select *from teacher where id=#{id}    
         </select>
</mapper>

2.1.3 测试

@Test
public void testStudent(){
   //第一步获取sqlsession对象
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
   List<Student> studentList = mapper.getStudent();
   for (Student student : studentList) {
       System.out.println(student);
   }
   sqlSession.close();
}

2.1.4 测试结果

在这里插入图片描述

2.2 按照结果嵌套处理

2.2.1 编写接口方法

public interface StudentMapper {
 //查询所有的学生信息，以及对应的老师信息
 List<Student> getStudent2();
}

2.2.2 编写sql标签

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"        
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.kuang.dao.StudentMapper">        
        <!--按照结果嵌套查询-->
        <select id="getStudent2" resultMap="StudentTeacher2">
                select s.id sid,s.name sname,t.name tname
                from student s,teacher t
                where s.tid =t.id;
        </select>
        <resultMap id="StudentTeacher2" type="Student">
                <result property="id" column="sid" />
                <result property="name" column="sname" />
                <association property="teacher" javaType="Teacher">            
                    <result property="name" column="tname"/>
                </association>           
        </resultMap>
</mapper>

2.2.3 测试

@Test
public void testStudent2(){
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
   List<Student> studentList = mapper.getStudent2();
   for (Student student : studentList) {
       System.out.println(student);
   }
   sqlSession.close();
}

2.2.4 测试结果

在这里插入图片描述

三、一对多复杂查询

3.1 按照结果嵌套查询

3.1.1 学生实体类

@Data
public class Student1 {
    private int id;
    private String name;
    private int tid;
    }

3.1.2 教师实体类

@Data
public class Teacher1 {
    private int id;
    private String name;
    //一个老师对应多个学生
    private List<Student1> students;
    }

3.1.3 编写接口

public interface TeacherMapper1 {
   //获取指定老师下的所有学生及老师的信息   
   Teacher1 getTeacher2(@Param("tid") int id);
   }

3.1.4 编写TeacherMapper1.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.kuang.dao.TeacherMapper1">
    <select id="getTeacher1" resultType="Teacher1">
        select *from mybatis.teacher;
    </select>
    <!--按照结果嵌套查询-->
    <select id="getTeacher2" resultMap="TeacherStudent1">
       select s.id sid,s.name sname,t.name tname,t.id tid
       from student s,teacher t
       where s.tid = t.id and t.id = #{tid};
    </select>

    <resultMap id="TeacherStudent1" type="Teacher1">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <!--复杂的属性：我们要单独处理 对象：association 集合：collection -->
        <!--javaType="" 指定属性的类型  集合中的泛型信息我们使用ofType获取-->
        <collection property="student1s" ofType="Student1" javaType="java.util.List" >
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>
</mapper>

3.1.5 测试

@Test
public void test2() {
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   TeacherMapper1 mapper = sqlSession.getMapper(TeacherMapper1.class);
   Teacher1 teacher = mapper.getTeacher2(1);
   System.out.println(teacher);
}

3.1.6 测试结果

在这里插入图片描述

3.2 根据查询嵌套处理

3.2.1 编写接口

public interface TeacherMapper1 {
   //获取指定老师下的所有学生及老师的信息
   Teacher1 getTeacher3(@Param("tid") int id);
}

3.2.2 编写TeacherMapper1.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.kuang.dao.TeacherMapper1">

    <select id="getTeacher3" resultType="com.kuang.pojo.Teacher1" resultMap="TeacherStudent2">
        select *from mybatis.teacher where id = #{tid};
    </select>
    
    <resultMap id="TeacherStudent2" type="Teacher1">
        <collection property="student1s" javaType="ArrayList" ofType="Student1" select="getStudentByTeacherId" column="id"/>
    </resultMap>
    
    <select id="getStudentByTeacherId" resultType="Student1">
        select *from mybatis.student where id = #{tid}
    </select>
</mapper>

3.2.3 测试

@Test
public void test2() {
   SqlSession sqlSession = MybatisUtils.getSqlSession();
   TeacherMapper1 mapper = sqlSession.getMapper(TeacherMapper1.class);
   Teacher1 teacher = mapper.getTeacher3(1);
   System.out.println(teacher);
}

3.2.4 测试结果

在这里插入图片描述

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