mybatis多表关联查询之resultMap单个对象

resultMap的n+1方式实现多表查询（多对一）

实体类

创建班级类（Clazz）和学生类（Student），并在Student中添加一个Clazz类型的属性，用于表示学生的班级信息。

mapper层

提供studentMapper和ClazzMapper，studentMapper查询所有学生的信息，ClazzMapper根据编号查询班级信息。再StudentMapper中使用<association>配置装配。

<association> 用于关联一个对象

property:用于关联一个对象。
select：设定要继续引用的查询，namespace+id
column：查询时需要传递的列

service层

由于装配已经完成，serivce层只需调用mapper即可，不需要再进行装配了。

测试代码

多表关联查询_resultMap_单个对象_N+1方式实现

1 package com.bjsxt.mapper;
2 
3 import com.bjsxt.pojo.Clazz;
4 
5 public interface ClazzMapper {
6 
7     Clazz selById(int id);
8 }

1 package com.bjsxt.mapper;
2 
3 import java.util.List;
4 
5 import com.bjsxt.pojo.Student;
6 
7 public interface StudentMapper {
8     List<Student> selAll();
9 }

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE mapper
 3   PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-|3-mapper.dtd">
 5  <mapper namespace="com.bjsxt.mapper.ClazzMapper">
 6   <select id="selById" resultType="clazz"  parameterType="int">
 7       select * from t_class where id=#{0}
 8   </select>
 9  
10  </mapper>
11

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE mapper
 3   PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-|3-mapper.dtd">
 5  <mapper namespace="com.bjsxt.mapper.StudentMapper">
 6      <resultMap type="student" id="smap">
 7          <id property="id" column="id"/>
 8          <result property="name" column="name"/>
 9          <result property="age" column="age"/>
10          <result property="gender" column="gender"/>
11          <result property="cid" column="cid"/>
12          <!-- 用于关联一个对象 -->
13          <association property="clazz" select="com.bjsxt.mapper.ClazzMapper.selById" column="cid"></association>
14      </resultMap>
15   <select id="selAll" resultMap="smap">
16       select * from t_student
17   </select>
18  
19  </mapper>
20

 1 package com.bjsxt.pojo;
 2 
 3 import java.io.Serializable;
 4 
 5 public class Clazz implements Serializable{
 6    private int id;
 7    private String name;
 8    private String room;
 9    
10 public int hashCode() {
11     final int prime = 31;
12     int result = 1;
13     result = prime * result + id;
14     result = prime * result + ((name == null) ? 0 : name.hashCode());
15     result = prime * result + ((room == null) ? 0 : room.hashCode());
16     return result;
17 }
18 public boolean equals(Object obj) {
19     if (this == obj)
20         return true;
21     if (obj == null)
22         return false;
23     if (getClass() != obj.getClass())
24         return false;
25     Clazz other = (Clazz) obj;
26     if (id != other.id)
27         return false;
28     if (name == null) {
29         if (other.name != null)
30             return false;
31     } else if (!name.equals(other.name))
32         return false;
33     if (room == null) {
34         if (other.room != null)
35             return false;
36     } else if (!room.equals(other.room))
37         return false;
38     return true;
39 }
40 public String toString() {
41     return "Clazz [id=" + id + ", name=" + name + ", room=" + room + "]";
42 }
43 public Clazz() {
44     super();
45     // TODO Auto-generated constructor stub
46 }
47 public Clazz(int id, String name, String room) {
48     super();
49     this.id = id;
50     this.name = name;
51     this.room = room;
52 }
53 public int getId() {
54     return id;
55 }
56 public void setId(int id) {
57     this.id = id;
58 }
59 public String getName() {
60     return name;
61 }
62 public void setName(String name) {
63     this.name = name;
64 }
65 public String getRoom() {
66     return room;
67 }
68 public void setRoom(String room) {
69     this.room = room;
70 }
71    
72 }

  1 package com.bjsxt.pojo;
  2 
  3 import java.io.Serializable;
  4 
  5 public class Student implements Serializable{
  6   private int id;
  7   private String name;
  8   private int age;
  9   private String gender;
 10  private int cid;
 11  private Clazz clazz;//用于封装班级信息
 12 public int hashCode() {
 13     final int prime = 31;
 14     int result = 1;
 15     result = prime * result + age;
 16     result = prime * result + cid;
 17     result = prime * result + ((clazz == null) ? 0 : clazz.hashCode());
 18     result = prime * result + ((gender == null) ? 0 : gender.hashCode());
 19     result = prime * result + id;
 20     result = prime * result + ((name == null) ? 0 : name.hashCode());
 21     return result;
 22 }
 23 public boolean equals(Object obj) {
 24     if (this == obj)
 25         return true;
 26     if (obj == null)
 27         return false;
 28     if (getClass() != obj.getClass())
 29         return false;
 30     Student other = (Student) obj;
 31     if (age != other.age)
 32         return false;
 33     if (cid != other.cid)
 34         return false;
 35     if (clazz == null) {
 36         if (other.clazz != null)
 37             return false;
 38     } else if (!clazz.equals(other.clazz))
 39         return false;
 40     if (gender == null) {
 41         if (other.gender != null)
 42             return false;
 43     } else if (!gender.equals(other.gender))
 44         return false;
 45     if (id != other.id)
 46         return false;
 47     if (name == null) {
 48         if (other.name != null)
 49             return false;
 50     } else if (!name.equals(other.name))
 51         return false;
 52     return true;
 53 }
 54 public String toString() {
 55     return "Student [id=" + id + ", name=" + name + ", age=" + age
 56             + ", gender=" + gender + ", cid=" + cid + ", clazz=" + clazz + "]";
 57 }
 58 public Student(int id, String name, int age, String gender, int cid, Clazz clazz) {
 59     super();
 60     this.id = id;
 61     this.name = name;
 62     this.age = age;
 63     this.gender = gender;
 64     this.cid = cid;
 65     this.clazz = clazz;
 66 }
 67 public Student() {
 68     super();
 69     // TODO Auto-generated constructor stub
 70 }
 71 public int getId() {
 72     return id;
 73 }
 74 public void setId(int id) {
 75     this.id = id;
 76 }
 77 public String getName() {
 78     return name;
 79 }
 80 public void setName(String name) {
 81     this.name = name;
 82 }
 83 public int getAge() {
 84     return age;
 85 }
 86 public void setAge(int age) {
 87     this.age = age;
 88 }
 89 public String getGender() {
 90     return gender;
 91 }
 92 public void setGender(String gender) {
 93     this.gender = gender;
 94 }
 95 public int getCid() {
 96     return cid;
 97 }
 98 public void setCid(int cid) {
 99     this.cid = cid;
100 }
101 public Clazz getClazz() {
102     return clazz;
103 }
104 public void setClazz(Clazz clazz) {
105     this.clazz = clazz;
106 }
107  
108 }

 1 package com.bjsxt.service;
 2 
 3 import java.util.List;
 4 
 5 import com.bjsxt.pojo.Student;
 6 
 7 public interface StudentService {
 8     List<Student> selAll();
 9 
10 }

 1 package com.bjsxt.service.impl;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.session.SqlSession;
 6 
 7 import com.bjsxt.mapper.ClazzMapper;
 8 import com.bjsxt.mapper.StudentMapper;
 9 import com.bjsxt.pojo.Clazz;
10 import com.bjsxt.pojo.Student;
11 import com.bjsxt.service.StudentService;
12 import com.bjsxt.util.MyBatisUtil;
13 
14 public class StudentServiceImpl implements StudentService{
15 
16     @Override
17     public List<Student> selAll() {
18         SqlSession session =MyBatisUtil.getSession();
19         
20         StudentMapper stuMapper = session.getMapper(StudentMapper.class);
21         List<Student> list = stuMapper.selAll();
22     
23         session.close();
24         return list;
25     }
26 
27 }

 1 package com.bjsxt.test;
 2 
 3 import java.util.List;
 4 
 5 import com.bjsxt.pojo.Student;
 6 import com.bjsxt.service.StudentService;
 7 import com.bjsxt.service.impl.StudentServiceImpl;
 8 
 9 public class TestQuery {
10 
11     public static void main(String[] args) {
12         StudentService ss=new StudentServiceImpl();
13         List<Student> list = ss.selAll();
14         for (Student student : list) {
15             System.out.println(student);
16         }
17         
18 
19     }
20 
21 }

 1 package com.bjsxt.util;
 2 
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 
 6 import org.apache.ibatis.io.Resources;
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 public class MyBatisUtil {
12     
13     private static SqlSessionFactory factory=null;
14     static{
15         
16         try {
17             InputStream is=Resources.getResourceAsStream("mybatis.xml");
18             factory=new SqlSessionFactoryBuilder().build(is);
19         } catch (IOException e) {
20             // TODO Auto-generated catch block
21             e.printStackTrace();
22         }
23     }
24 
25     public static SqlSession getSession(){
26         SqlSession session =null;
27         if(factory!=null){
28             //true表示开启
29          session= factory.openSession(true);
30         }
31         return session;
32     }
33 }

1 jdbc.driver=com.mysql.jdbc.Driver
2 jdbc.url=jdbc:mysql://localhost:3306/java505?useSSL=true&amp;characterEncoding=utf8&amp;useSSL=true
3 jdbc.username=root
4 jdbc.password=root

 1 # Set root category priority to INFO and its only appender to CONSOLE.
 2 log4j.rootCategory=ERROR, CONSOLE
 3 # log4j.rootCategory=DEBUG, CONSOLE, LOGFILE
 4 
 5 # 单独设置SQL语句的输出级别为DEBUG级别
 6 log4j.logger.com.bjsxt.mapper=DEBUG
 7 
 8 # CONSOLE is set to be a ConsoleAppender using a PatternLayout.
 9 log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
10 log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
11 log4j.appender.CONSOLE.layout.ConversionPattern=- %m%n
12 
13 # LOGFILE is set to be a File appender using a PatternLayout.
14 log4j.appender.LOGFILE=org.apache.log4j.FileAppender
15 log4j.appender.LOGFILE.File=d:/test.log
16 log4j.appender.LOGFILE.Append=true
17 log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
18 log4j.appender.LOGFILE.layout.ConversionPattern=- %m %l%n

 1 <?xml version="1.0" encoding="UTF-8" ?>
 2 <!DOCTYPE configuration
 3   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5   <configuration>
 6       <properties resource="db.properties"/>
 7       <settings>
 8           <!-- 设置MyBatis使用log4j日志支持 -->
 9           <setting name="logImpl" value="LOG4J"/>
10       </settings>
11       <!-- typeAliases给类型取别名 -->
12       <typeAliases>
13           <!-- 给user类取别名 -->
14           <!-- <typeAlias type="com.bjsxt.pojo.User" alias="u"/> -->
15           <!-- 别名都是类的名字 -->
16           <package name="com.bjsxt.pojo"/>
17       </typeAliases>
18       <!-- 用于指定使用哪个开发
19                                 用于指定使用的环境id
20        -->
21       <environments default="dev">
22           <!-- 用于配置开发环境
23                id：环境的唯一识别码
24            -->
25           <environment id="dev">
26               <!-- 事务管理器
27                    type：用于设定mybatis采用什么方式管理事务
28                    JDBC表示和JDBC一样事务的管理方式
29                -->
30               <transactionManager type="JDBC"/>
31               <!-- 数据源/连接池
32                                                          用于配置链接池和数据库链接的参数
33                    type：用于设置mybatis是否采用链接池技术
34                                                         连接池：用来存数据库链接的，减少数据库的频繁开关
35                    POOLED表示mybatis采用连接池技术                                     
36                -->
37               <dataSource type="POOLED">
38                   <property name="driver" value="${jdbc.driver}"/>
39                   <property name="url" value="${jdbc.url}"/>
40                   <property name="username" value="${jdbc.username}"/>
41                   <property name="password" value="${jdbc.password}"/>
42               </dataSource>
43           </environment>
44       </environments>
45       <!-- 扫描mapper文件 -->
46       <!-- 文件的全限制路径要用/ -->
47       <mappers>
48        <!--    <mapper class="com.bjsxt.mapper.UserMapper"/> -->
49        <package name="com.bjsxt.mapper"/>
50        
51       </mappers>
52   </configuration>

多表关联查询_resultMap_单个对象_关联方式实现

package com.bjsxt.mapper;

import java.util.List;

import com.bjsxt.pojo.Student;

public interface StudentMapper {

    List<Student> selAll();
}

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3   PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 <mapper namespace="com.bjsxt.mapper.StudentMapper">
 6     <resultMap type="student" id="smap">
 7         <id property="id" column="sid" />
 8         <result property="name" column="sname" />
 9         <result property="age" column="age" />
10         <result property="gender" column="gender" />
11         <result property="cid" column="cid" />
12         <association property="clazz" javaType="clazz">
13             <id property="id" column="cid" />
14             <result property="name" column="cname" />
15             <result property="room" column="room" />
16         </association>
17     </resultMap>
18     <select id="selAll" resultMap="smap">
19         select s.id sid, s.name sname, s.age, s.gender, c.id cid, c.name cname, c.room
20         from t_student s
21         left join t_class c
22         on s.cid=c.id
23     </select>
24 </mapper>

 1 package com.bjsxt.pojo;
 2 
 3 import java.io.Serializable;
 4 
 5 public class Clazz implements Serializable {
 6 
 7     private int id;
 8     private String name;
 9     private String room;
10 
11     public Clazz() {
12         super();
13     }
14 
15     public int getId() {
16         return id;
17     }
18 
19     public void setId(int id) {
20         this.id = id;
21     }
22 
23     public String getName() {
24         return name;
25     }
26 
27     public void setName(String name) {
28         this.name = name;
29     }
30 
31     public String getRoom() {
32         return room;
33     }
34 
35     public void setRoom(String room) {
36         this.room = room;
37     }
38 
39     @Override
40     public int hashCode() {
41         final int prime = 31;
42         int result = 1;
43         result = prime * result + id;
44         result = prime * result + ((name == null) ? 0 : name.hashCode());
45         result = prime * result + ((room == null) ? 0 : room.hashCode());
46         return result;
47     }
48 
49     @Override
50     public boolean equals(Object obj) {
51         if (this == obj)
52             return true;
53         if (obj == null)
54             return false;
55         if (getClass() != obj.getClass())
56             return false;
57         Clazz other = (Clazz) obj;
58         if (id != other.id)
59             return false;
60         if (name == null) {
61             if (other.name != null)
62                 return false;
63         } else if (!name.equals(other.name))
64             return false;
65         if (room == null) {
66             if (other.room != null)
67                 return false;
68         } else if (!room.equals(other.room))
69             return false;
70         return true;
71     }
72 
73     @Override
74     public String toString() {
75         return "Clazz [id=" + id + ", name=" + name + ", room=" + room + "]";
76     }
77 }

  1 package com.bjsxt.pojo;
  2 
  3 import java.io.Serializable;
  4 
  5 public class Student implements Serializable {
  6 
  7     private int id;
  8     private String name;
  9     private int age;
 10     private String gender;
 11     private int cid;
 12     private Clazz clazz;// 用于封装班级信息
 13 
 14     public Student() {
 15         super();
 16     }
 17 
 18     public int getId() {
 19         return id;
 20     }
 21 
 22     public void setId(int id) {
 23         this.id = id;
 24     }
 25 
 26     public String getName() {
 27         return name;
 28     }
 29 
 30     public void setName(String name) {
 31         this.name = name;
 32     }
 33 
 34     public int getAge() {
 35         return age;
 36     }
 37 
 38     public void setAge(int age) {
 39         this.age = age;
 40     }
 41 
 42     public String getGender() {
 43         return gender;
 44     }
 45 
 46     public void setGender(String gender) {
 47         this.gender = gender;
 48     }
 49 
 50     public int getCid() {
 51         return cid;
 52     }
 53 
 54     public void setCid(int cid) {
 55         this.cid = cid;
 56     }
 57 
 58     public Clazz getClazz() {
 59         return clazz;
 60     }
 61 
 62     public void setClazz(Clazz clazz) {
 63         this.clazz = clazz;
 64     }
 65 
 66     @Override
 67     public int hashCode() {
 68         final int prime = 31;
 69         int result = 1;
 70         result = prime * result + age;
 71         result = prime * result + cid;
 72         result = prime * result + ((clazz == null) ? 0 : clazz.hashCode());
 73         result = prime * result + ((gender == null) ? 0 : gender.hashCode());
 74         result = prime * result + id;
 75         result = prime * result + ((name == null) ? 0 : name.hashCode());
 76         return result;
 77     }
 78 
 79     @Override
 80     public boolean equals(Object obj) {
 81         if (this == obj)
 82             return true;
 83         if (obj == null)
 84             return false;
 85         if (getClass() != obj.getClass())
 86             return false;
 87         Student other = (Student) obj;
 88         if (age != other.age)
 89             return false;
 90         if (cid != other.cid)
 91             return false;
 92         if (clazz == null) {
 93             if (other.clazz != null)
 94                 return false;
 95         } else if (!clazz.equals(other.clazz))
 96             return false;
 97         if (gender == null) {
 98             if (other.gender != null)
 99                 return false;
100         } else if (!gender.equals(other.gender))
101             return false;
102         if (id != other.id)
103             return false;
104         if (name == null) {
105             if (other.name != null)
106                 return false;
107         } else if (!name.equals(other.name))
108             return false;
109         return true;
110     }
111 
112     @Override
113     public String toString() {
114         return "Student [id=" + id + ", name=" + name + ", age=" + age + ", gender=" + gender + ", cid=" + cid
115                 + ", clazz=" + clazz + "]";
116     }
117 }

 1 package com.bjsxt.service;
 2 
 3 import java.util.List;
 4 
 5 import com.bjsxt.pojo.Student;
 6 
 7 public interface StudentService {
 8 
 9     List<Student> selAll();
10 }

 1 package com.bjsxt.service.impl;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.session.SqlSession;
 6 
 7 import com.bjsxt.mapper.StudentMapper;
 8 import com.bjsxt.pojo.Student;
 9 import com.bjsxt.service.StudentService;
10 import com.bjsxt.util.MyBatisUtil;
11 
12 public class StudentServiceImpl implements StudentService {
13 
14     public List<Student> selAll() {
15         SqlSession session = MyBatisUtil.getSession();
16 
17         // 学生mapper
18         StudentMapper stuMapper = session.getMapper(StudentMapper.class);
19 
20         List<Student> list = stuMapper.selAll();
21 
22         session.close();
23         return list;
24     }
25 
26 }

 1 package com.bjsxt.test;
 2 
 3 import java.util.List;
 4 
 5 import com.bjsxt.pojo.Student;
 6 import com.bjsxt.service.StudentService;
 7 import com.bjsxt.service.impl.StudentServiceImpl;
 8 
 9 public class TestQuery {
10 
11     public static void main(String[] args) {
12         StudentService ss = new StudentServiceImpl();
13         List<Student> list = ss.selAll();
14         for (Student student : list) {
15             System.out.println(student);
16         }
17     }
18 
19 }

 1 package com.bjsxt.util;
 2 
 3 import java.io.IOException;
 4 import java.io.InputStream;
 5 
 6 import org.apache.ibatis.io.Resources;
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.ibatis.session.SqlSessionFactory;
 9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
10 
11 public class MyBatisUtil {
12 
13     private static SqlSessionFactory factory = null;
14 
15     static {
16         try {
17             InputStream is = Resources.getResourceAsStream("mybatis-cfg.xml");
18             factory = new SqlSessionFactoryBuilder().build(is);
19         } catch (IOException e) {
20             e.printStackTrace();
21         }
22     }
23 
24     public static SqlSession getSession() {
25         SqlSession session = null;
26         if (factory != null) {
27             // true表示开启自动提交
28             // session = factory.openSession(true);
29             session = factory.openSession();
30         }
31         return session;
32     }
33 }

1 jdbc.driver=com.mysql.jdbc.Driver
2 jdbc.url=jdbc:mysql://localhost:3306/java505
3 jdbc.username=root
4 jdbc.password=root

 1 # Set root category priority to INFO and its only appender to CONSOLE.
 2 log4j.rootCategory=ERROR, CONSOLE
 3 # log4j.rootCategory=DEBUG, CONSOLE, LOGFILE
 4 
 5 # 单独设置SQL语句的输出级别为DEBUG级别
 6 log4j.logger.com.bjsxt.mapper=DEBUG
 7 
 8 # CONSOLE is set to be a ConsoleAppender using a PatternLayout.
 9 log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
10 log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
11 log4j.appender.CONSOLE.layout.ConversionPattern=- %m%n
12 
13 # LOGFILE is set to be a File appender using a PatternLayout.
14 log4j.appender.LOGFILE=org.apache.log4j.FileAppender
15 log4j.appender.LOGFILE.File=d:/test.log
16 log4j.appender.LOGFILE.Append=true
17 log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
18 log4j.appender.LOGFILE.layout.ConversionPattern=- %m %l%n

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE configuration
 3   PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 4   "http://mybatis.org/dtd/mybatis-3-config.dtd">
 5 <configuration>
 6     <!-- properties加载外部文件 -->
 7     <properties resource="db.properties" />
 8     <!-- settings标签 -->
 9     <settings>
10         <!-- 设置MyBatis使用log4j日志支持 -->
11         <setting name="logImpl" value="LOG4J"/>
12     </settings>
13     <!-- typeAliases给类型起别名 -->
14     <typeAliases>
15         <package name="com.bjsxt.pojo" />
16     </typeAliases>
17     <environments default="dev">
18         <environment id="dev">
19             <transactionManager type="JDBC" />
20             <dataSource type="POOLED">
21                 <property name="driver" value="${jdbc.driver}"/>
22                 <property name="url" value="${jdbc.url}"/>
23                 <property name="username" value="${jdbc.username}"/>
24                 <property name="password" value="${jdbc.password}"/>
25             </dataSource>
26         </environment>
27     </environments>
28     <mappers>
29         <package name="com.bjsxt.mapper" />
30     </mappers>
31 </configuration>