Ibatis 简明教程

iBATIS - Read Operation

我们在上一章中讨论了如何使用 iBATIS 对表执行 CREATE 操作。本章将说明如何使用 iBATIS 读取表。

We discussed, in the last chapter, how to perform CREATE operation on a table using iBATIS. This chapter explains how to read a table using iBATIS.

我们在 MySQL 中有以下“员工”表——

We have the following EMPLOYEE table in MySQL −

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)
);

此表仅有一个记录，如下所示 -

This table has only one record as follows −

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，我们将在 Employee.java 中修改 Employee 类，如下所示：

To perform read operation, we would modify the Employee class in Employee.java as follows −

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

为了使用 iBATIS 定义 SQL 映射语句，我们将在 Employee.xml 文件中添加 <select> 标记，在该标记定义中，我们将定义一个将在 IbatisRead.java 文件中用于对数据库执行 SQL SELECT 查询的“id”。

To define SQL mapping statement using iBATIS, we would add <select> tag in Employee.xml file and inside this tag definition, we would define an "id" which will be used in IbatisRead.java file for executing SQL SELECT query on database.

<?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>

此处，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使用 WHERE 子句与 SELECT 语句一起使用，以及如何将值传递给该 WHERE 子句。

Here we did not use WHERE clause with SQL SELECT statement. We would demonstrate, in the next chapter, how you can use WHERE clause with SELECT statement and how you can pass values to that WHERE clause.

IbatisRead.java File

该文件具有从 Employee 表读取记录的应用程序级逻辑：

This file has application level logic to read records from the Employee table −

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 ");
   }
}

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。

Here are the steps to compile and run the above mentioned software. Make sure you have set PATH and CLASSPATH appropriately before proceeding for compilation and execution.

Create Employee.xml as shown above.
Create Employee.java as shown above and compile it.
Create IbatisRead.java as shown above and compile it.
Execute IbatisRead binary to run the program.

你会获得以下结果，并且会从 EMPLOYEE 表中读取一条记录，如下所示：

You would get the following result, and a record would be read from the EMPLOYEE table as follows −

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