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
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
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1 package com.bjsxt.mapper; 2[
3 import com.bjsxt.pojo.Clazz; 4
5 public interface ClazzMapper { 6
7 Clazz selById(int id); 8 }
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1 package com.bjsxt.mapper; 2[
3 import java.util.List; 4
5 import com.bjsxt.pojo.Student; 6
7 public interface StudentMapper { 8 ListselAll(); 9 }
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1[
2 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4 "http://mybatis.org/dtd/mybatis-|3-mapper.dtd">
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1[
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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 }
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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 }
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1 package com.bjsxt.service; 2[
3 import java.util.List; 4
5 import com.bjsxt.pojo.Student; 6
7 public interface StudentService { 8 ListselAll(); 9
10 }
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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 ListselAll() { 18 SqlSession session =MyBatisUtil.getSession(); 19
20 StudentMapper stuMapper = session.getMapper(StudentMapper.class); 21 Listlist = stuMapper.selAll(); 22
23 session.close(); 24 return list; 25 } 26
27 }
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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 Listlist = ss.selAll(); 14 for (Student student : list) { 15 System.out.println(student); 16 } 17
18
19 } 20
21 }
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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 }
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1 jdbc.driver=com.mysql.jdbc.Driver 2 jdbc.url=jdbc:mysql://localhost:3306/java505?useSSL=true&characterEncoding=utf8&useSSL=true[
3 jdbc.username=root 4 jdbc.password=root
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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
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1[
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多表关联查询resultMap单个对象_关联方式实现
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package com.bjsxt.mapper; import java.util.List; import com.bjsxt.pojo.Student; public interface StudentMapper {
List selAll();
}
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1[
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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 }
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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 }
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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 ListselAll(); 10 }
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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 ListselAll() { 15 SqlSession session = MyBatisUtil.getSession(); 16
17 // 学生mapper
18 StudentMapper stuMapper = session.getMapper(StudentMapper.class); 19
20 Listlist = stuMapper.selAll(); 21
22 session.close(); 23 return list; 24 } 25
26 }
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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 Listlist = ss.selAll(); 14 for (Student student : list) { 15 System.out.println(student); 16 } 17 } 18
19 }
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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 }
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1 jdbc.driver=com.mysql.jdbc.Driver 2 jdbc.url=jdbc:mysql://localhost:3306/java505[
3 jdbc.username=root 4 jdbc.password=root
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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
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https://www.cnblogs.com/wq-9/p/10238824.html