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  MyBatis 注解

  • 注解

    在前面的章节中，我们已经了解了如何使用MyBatis执行CURD操作。在那里，我们使用了一个Mapper XML文件来存储映射的SQL语句，并使用一个配置XML文件来配置MyBatis。
    为了映射SQL语句，MyBatis还提供了注解。因此，本章讨论如何使用MyBatis注解。
    在处理注解时，我们可以使用Java mapper接口来映射和执行SQL查询，而不是配置XML文件。
    假设，我们在MySQL中具有以下employee表： 
    
CREATE TABLE details.student(
   ID int(10) NOT NULL AUTO_INCREMENT,
   NAME varchar(100) NOT NULL,
   BRANCH varchar(255) NOT NULL,
   PERCENTAGE int(3) NOT NULL,
   PHONE int(11) NOT NULL,
   EMAIL varchar(255) NOT NULL,
   PRIMARY KEY (`ID`)
);
Query OK, 0 rows affected (0.37 sec)
    假设此表具有两个记录，如下所示- 
    
mysql> select * from STUDENT;
+----+----------+--------+------------+-----------+--------------------+
| ID |  NAME    | BRANCH | PERCENTAGE |   PHONE   |      EMAIL         |
+----+----------+--------+------------+-----------+--------------------+
|  1 | Mohammad |   It   |    80      | 984803322 | Mohammad@gmail.com |
|  2 | Shyam    |   It   |    75      | 984800000 | shyam@gmail.com    |
+----+----------+--------+------------+-----------+--------------------+

  • Student POJO类

    POJO类将具有执行所需操作所需的所有方法的实现。 在Student.java文件中将Student类创建为- 
    
public class Student {
   private int id;
   private String name;
   private String branch;
   private int percentage;
   private int phone;
   private String email;

   public Student(int id, String name, String branch, int percentage, int phone, String email) {
      super();
      this.id = id;
      this.name = name;
      this.branch = branch;
      this.percentage = percentage;
      this.phone = phone;
      this.email = email;
   }
        
   public Student() {}

   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 int getPhone() {
      return phone;
   }
        
   public void setPhone(int phone) {
      this.phone = phone;
   }
        
   public String getEmail() {
      return email;
   }
        
   public void setEmail(String email) {
      this.email = email;
   }

   public String getBranch() {
      return branch;
   }

   public void setBranch(String branch) {
      this.branch = branch;
   }

   public int getPercentage() {
      return percentage;
   }

   public void setPercentage(int percentage) {
      this.percentage = percentage;
   }    
  
}

  • Student_mapper.java

    这是文件，其中包含映射器接口，我们在其中使用批注而不是XML标签声明映射的语句。对于几乎所有基于XML的映射器元素，MyBatis都提供了注释。以下名为Student_mapper.java的文件包含一个映射器接口。在此文件中，您可以看到对STUDENT表执行CURD操作的注释。 
    
import java.util.List;

import org.apache.ibatis.annotations.*;

public interface Student_mapper {
        
   final String getAll = "SELECT * FROM STUDENT"; 
   final String getById = "SELECT * FROM STUDENT WHERE ID = #{id}";
   final String deleteById = "DELETE from STUDENT WHERE ID = #{id}";
   final String insert = "INSERT INTO STUDENT (NAME, BRANCH, PERCENTAGE, PHONE, EMAIL ) VALUES (#{name}, #{branch}, #{percentage}, #{phone}, #{email})";
   final String update = "UPDATE STUDENT SET EMAIL = #{email}, NAME = #{name}, BRANCH = #{branch}, PERCENTAGE = #{percentage}, PHONE = #{phone} WHERE ID = #{id}";
   
   @Select(getAll)
   @Results(value = {
      @Result(property = "id", column = "ID"),
      @Result(property = "name", column = "NAME"),
      @Result(property = "branch", column = "BRANCH"),
      @Result(property = "percentage", column = "PERCENTAGE"),       
      @Result(property = "phone", column = "PHONE"),
      @Result(property = "email", column = "EMAIL")
   })
   
   List getAll();
  
   @Select(getById)
   @Results(value = {
      @Result(property = "id", column = "ID"),
      @Result(property = "name", column = "NAME"),
      @Result(property = "branch", column = "BRANCH"),
      @Result(property = "percentage", column = "PERCENTAGE"),       
      @Result(property = "phone", column = "PHONE"),
      @Result(property = "email", column = "EMAIL")
   })
   
   Student getById(int id);

   @Update(update)
   void update(Student student);

   @Delete(deleteById)
   void delete(int id);
  
   @Insert(insert)
   @Options(useGeneratedKeys = true, keyProperty = "id")
   void insert(Student student);
}

  • Annotations_Example.java文件

    该文件将具有应用程序级逻辑，以将记录插入到Student表中。创建并保存mybatisInsert.java文件，如下所示- 
    
import java.io.IOException;
import java.io.Reader;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Annotations_Example { 

   public static void main(String args[]) throws IOException{
      
      Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml");
      SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);               
      SqlSession session = sqlSessionFactory.openSession();
      session.getConfiguration().addMapper(Student_mapper.class);
      
      Student_mapper mapper = session.getMapper(Student_mapper.class);      
      
      //Create a new student object
      Student student = new Student();
      
      //Set the values      
      student.setName("zara");
      student.setBranch("EEE");
      student.setEmail("zara@gmail.com");
      student.setPercentage(90));
      student.setPhone(123412341);
            
      //Insert student data   
      mapper.insert(student);
      System.out.println("record inserted successfully");
      session.commit();
      session.close();
                        
   }
   
}

  • 编译并运行

    这是编译和运行Annotations_Example.java文件的步骤。在继续进行编译和执行之前，请确保已正确设置了PATH和CLASSPATH。
    • 如上所示创建Student.xml。
    • 如本教程的MYBATIS-配置XML章节中所示，创建SqlMapConfig.xml 。
    • 如上所示创建Student.java并进行编译。
    • 如上所示创建Annotations_Example.java并进行编译。
    • 执行Annotations_Example二进制文件以运行程序。
    您将得到以下结果，并且将在STUDENT表中创建一条记录。 
    
$java Annotations_Example
Record Inserted Successfully
    如果检查student表，它将显示以下结果- 
    
mysql> select * from student;
+----+----------+--------+------------+-----------+----------------------+
| ID | NAME     | BRANCH | PERCENTAGE |   PHONE   |        EMAIL         |
+----+----------+--------+------------+-----------+----------------------+
|  1 | Mohammad |  It    |     80     | 900000000 | mohamad123@yahoo.com |
|  2 | Shyam    |  It    |     75     | 984800000 | shyam@gmail.com      |
|  3 | Zara     |  EEE   |     90     | 123412341 | zara@gmail.com       |
+----+----------+--------+------------+-----------+----------------------+
3 rows in set (0.08 sec)
    以相同的方式，我们可以使用注释执行更新，删除和读取操作，方法是将Annotations_Example.java的内容替换为下面提到的各个代码片段-
    UPDATE 
    
public static void main(String args[]) throws IOException{
      
   Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml");
   SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);          
   SqlSession session = sqlSessionFactory.openSession();   
   session.getConfiguration().addMapper(Student_mapper.class);
   Student_mapper mapper = session.getMapper(Student_mapper.class); 
      
   //select a particular student using id               
   Student student = mapper.getById(2);
   System.out.println("Current details of the student are "+student.toString());  
      
   //Set new values to the mail and phone number of the student
   student.setEmail("Shyam123@yahoo.com");
   student.setPhone(984802233);
      
   //Update the student record
   mapper.update(student);
   System.out.println("Record updated successfully");   
   session.commit();   
   session.close();

}
    SELECT 
    
public static void main(String args[]) throws IOException{
      
   Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml");
   SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);          
   SqlSession session = sqlSessionFactory.openSession();
   session.getConfiguration().addMapper(Student_mapper.class);      
   Student_mapper mapper = session.getMapper(Student_mapper.class);
      
   //Get the student details
   Student student = mapper.getById(2);
   System.out.println(student.getBranch());
   System.out.println(student.getEmail());
   System.out.println(student.getId());
   System.out.println(student.getName());
   System.out.println(student.getPercentage());
   System.out.println(student.getPhone());      
   session.commit();
   session.close();
                        
}
    DELETE 
    
public static void main(String args[]) throws IOException{
      
   Reader reader = Resources.getResourceAsReader("SqlMapConfig.xml");
   SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);          
   SqlSession session = sqlSessionFactory.openSession();
   session.getConfiguration().addMapper(Student_mapper.class);
      
   Student_mapper mapper = session.getMapper(Student_mapper.class);
   mapper.delete(2);
   System.out.println("record deleted successfully");
   session.commit();
   session.close();            
                        
}
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