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。
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)
);此表仅有一个记录，如下所示 -
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：
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”。
<?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。
IbatisRead.java File
该文件具有从 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 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 ");
}
}