Result Maps

resultMap元素是iBATIS中最重要和最强大的元素。 您可以使用iBATIS ResultMap减少高达90％的JDBC编码，在某些情况下，它允许您执行JDBC甚至不支持的操作。

ResultMaps的设计使得简单语句根本不需要显式结果映射，而更复杂的语句只需要描述关系的绝对必要。

本章仅提供iBATIS ResultMaps的简单介绍。

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)
);

该表有两条记录如下 -

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
|  1 | Zara       | Ali       |   5000 |
|  2 | Roma       | Ali       |   3000 |
+----+------------+-----------+--------+
2 row in set (0.00 sec)

Employee POJO Class

要使用iBATIS ResultMap，您无​​需修改​​Employee.java文件。 让我们保持原样在最后一章。

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 required method definitions */
   public int getId() {
      return id;
   }
   public void setId(int id) {
      this.id = id;
   }
   public String getFirstName() {
      return first_name;
   }
   public void setFirstName(String fname) {
      this.first_name = fname;
   }
   public String getLastName() {
      return last_name;
   }
   public void setlastName(String lname) {
      this.last_name = lname;
   }
   public int getSalary() {
      return salary;
   }
   public void setSalary(int salary) {
      this.salary = salary;
   }
} /* End of Employee */

Employee.xml File

在这里，我们将修改Employee.xml以引入 resultMap>标记。 此标记将具有在我们的标记的resultMap属性中运行此resultMap所需的id。

<?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">
   <!-- Perform Insert Operation -->
   <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>
   <!-- Perform Read Operation -->
   <select id="getAll" resultClass="Employee">
      SELECT * FROM EMPLOYEE
   </select>
   <!-- Perform Update Operation -->
   <update id="update" parameterClass="Employee">
      UPDATE EMPLOYEE
      SET    first_name = #first_name#
      WHERE  id = #id#
    </update>
   <!-- Perform Delete Operation -->
   <delete id="delete" parameterClass="int">
      DELETE FROM EMPLOYEE
      WHERE  id = #id#
   </delete>
   <!-- Using ResultMap -->
   <resultMap id="result">
      <result property="id" column="id"/>
      <result property="first_name" column="first_name"/>
      <result property="last_name" column="last_name"/>
      <result property="salary" column="salary"/>
   </resultMap> 
   <select id="useResultMap" resultMap="result">
      SELECT * FROM EMPLOYEE
      WHERE id=#id#
   </select>
</sqlMap>

IbatisResultMap.java File

此文件具有应用程序级逻辑，可使用ResultMap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 IbatisResultMap{
   public static void main(String[] args)
   throws IOException,SQLException{
      Reader rd = Resources.getResourceAsReader("SqlMapConfig.xml");
      SqlMapClient smc = SqlMapClientBuilder.buildSqlMapClient(rd);
      int id = 1;
      System.out.println("Going to read record.....");
      Employee e = (Employee)smc.queryForObject ("Employee.useResultMap", id);
      System.out.println("ID:  " + e.getId());
      System.out.println("First Name:  " + e.getFirstName());
      System.out.println("Last Name:  " + e.getLastName());
      System.out.println("Salary:  " + e.getSalary());
      System.out.println("Record 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IbatisResultMap.java并进行编译。
• 执行IbatisResultMap二进制文件来运行程序。

您将获得以下结果，这是EMPLOYEE表上的读取操作。

Going to read record.....
ID:  1
First Name:  Zara
Last Name:  Ali
Salary:  5000
Record read Successfully