Ibatis 简明教程

iBATIS - Result Maps

resultMap 元素是 iBATIS 中最重要的并且功能最强的元素。使用 iBATIS ResultMap 可以减少高达 90% 的 JDBC 编码，并且在某些情况下，它允许你执行 JDBC 甚至不支持的操作。

ResultMaps 的设计使得对于简单的语句根本不需要明确的结果映射，而对于更复杂的语句，不需要指定超出绝对必要的范围来描述关系的信息。

本章仅简单介绍 iBATIS ResultMaps。

我们在 MySQL 中有以下“员工”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)
);

此表有两个记录，如下所示：

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，你不必修改 Employee.java 文件。让我们将其保持在上一个章节中的样子。

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></resultMap> 标记。此标记将具有一个 id，我们的 <select> 标记的 resultMap 属性需要它才能运行该 resultMap。

<?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" class="Employee">
      <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

此文件具有使用 ResultMap 从 Employee 表读取记录的应用程序级逻辑：

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 ");
   }
}

Compilation and Run

以下是如何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。

按上述方式创建 Employee.xml。
按上述方式创建 Employee.java 并对其进行编译。
按照上面显示的方式创建 IbatisResultMap.java 并对其进行编译。
执行 IbatisResultMap 二进制文件以运行该程序。

你会得到在 EMPLOYEE 表上执行的读取操作，其结果如下。

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