Read Operation

在上一章中，我们讨论了如何使用iBATIS对表执行CREATE操作。 本章介绍如何使用iBATIS读取表。

我们在MySQL中有以下EMPLOYEE表 -

CREATE TABLE EMPLOYEE (
   id INT NOT NULL auto_increment,
   first_name VARCHAR(20) default NULL,
   last_name  VARCHAR(20) default NULL,
   salary     INT  default NULL,
   PRIMARY KEY (id)
);

该表只有一条记录如下 -

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
|  1 | Zara       | Ali       |   5000 |
+----+------------+-----------+--------+
1 row in set (0.00 sec)

Employee POJO Class

要执行读取操作，我们将修改Employee.java中的Employee类，如下所示 -

public class Employee {
   private int id;
   private String first_name; 
   private String last_name;   
   private int salary;  
   /* Define constructors for the Employee class. */
   public Employee() {}
   public Employee(String fname, String lname, int salary) {
      this.first_name = fname;
      this.last_name = lname;
      this.salary = salary;
   }
   /* Here are the method definitions */
   public int getId() {
      return id;
   }
   public String getFirstName() {
      return first_name;
   }
   public String getLastName() {
      return last_name;
   }
   public int getSalary() {
      return salary;
   }
} /* End of Employee */

Employee.xml File

要使用iBATIS定义SQL映射语句，我们将在Employee.xml文件中添加标记，在此标记定义中，我们将定义一个“id”，它将在IbatisRead.java文件中用于在数据库上执行SQL SELECT查询。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN" "http://ibatis.apache.org/dtd/sql-map-2.dtd">
<sqlMap namespace="Employee">
   <insert id="insert" parameterClass="Employee">
      INSERT INTO EMPLOYEE(first_name, last_name, salary)
      values (#first_name#, #last_name#, #salary#)
      <selectKey resultClass="int" keyProperty="id">
         select last_insert_id() as id
      </selectKey>
   </insert>
   <select id="getAll" resultClass="Employee">
      SELECT * FROM EMPLOYEE
   </select>
</sqlMap>

这里我们没有将WHERE子句与SQL SELECT语句一起使用。 我们将在下一章中演示如何在SELECT语句中使用WHERE子句以及如何将值传递给该WHERE子句。

IbatisRead.java File

此文件具有应用程序级逻辑，用于从Employee表中读取记录 -

import com.ibatis.common.resources.Resources;
import com.ibatis.sqlmap.client.SqlMapClient;
import com.ibatis.sqlmap.client.SqlMapClientBuilder;
import java.io.*;
import java.sql.SQLException;
import java.util.*;
public class IbatisRead{
   public static void main(String[] args)throws IOException,SQLException{
      Reader rd = Resources.getResourceAsReader("SqlMapConfig.xml");
      SqlMapClient smc = SqlMapClientBuilder.buildSqlMapClient(rd);
      /* This would read all records from the Employee table. */
      System.out.println("Going to read records.....");
      List <Employee> ems = (List<Employee>)
         smc.queryForList("Employee.getAll", null);
      Employee em = null;
      for (Employee e : ems) {
         System.out.print("  " + e.getId());
         System.out.print("  " + e.getFirstName());
         System.out.print("  " + e.getLastName());
         System.out.print("  " + e.getSalary());
         em = e; 
         System.out.println("");
      }    
      System.out.println("Records Read Successfully ");
   }
} 

编译和运行 (Compilation and Run)

以下是编译和运行上述软件的步骤。 在继续编译和执行之前，请确保已正确设置PATH和CLASSPATH。

• 创建Employee.xml，如上所示。
• 如上所示创建Employee.java并编译它。
• 如上所示创建IbatisRead.java并编译它。
• 执行IbatisRead二进制文件来运行程序。

您将获得以下结果，并且将从EMPLOYEE表中读取记录，如下所示 -

Going to read records.....
   1  Zara  Ali  5000
Record Reads Successfully