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。

The resultMap element is the most important and powerful element in iBATIS. You can reduce up to 90% JDBC coding using iBATIS ResultMap and in some cases, it allows you to do things that JDBC does not even support.

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。

The design of ResultMaps is such that simple statements don’t require explicit result mappings at all, and more complex statements require no more than is absolutely necessary to describe the relationships.

本章仅简单介绍 iBATIS ResultMaps。

This chapter provides just a simple introduction of iBATIS ResultMaps.

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)
);

此表有两个记录，如下所示：

This table has two records as follows −

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。

To use iBATIS ResultMap, you do not need to modify the Employee.java file. Let us keep it as it was in the last chapter.

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。

Here we would modify Employee.xml to introduce <resultMap></resultMap> tag. This tag would have an id which is required to run this resultMap in our <select> tag’s resultMap attribute.

<?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：

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

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。

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.

  1. Create Employee.xml as shown above.

  2. Create Employee.java as shown above and compile it.

  3. Create IbatisResultMap.java as shown above and compile it.

  4. Execute IbatisResultMap binary to run the program.

你会得到在 EMPLOYEE 表上执行的读取操作，其结果如下。

You would get the following result which is a read operation on the EMPLOYEE table.

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