Hibernate的Trafodion方言

對象-關係映射(ORM)提供了一個框架，應用程序可使用一個對象範例，查詢並操做數據庫中的數據。該框架以多種語言實現，封裝了數據操做所需的代碼。這樣，您無需瞭解SQL，便可使用一個對象訪問數據，該對象隱藏了每一個數據庫查詢語言的變化。

假設有如下的Employees表：

ID	Name	Address	Department	Salary
1	John	Milpitas, CA	Engineer	$100,000
2	Tom	Cupertino, CA	Support	$80,000
3	James	Sunnyvale, CA	Pubs	$70,000
4	Mike	San Jose, CA	Marketing	$95,000
5	Maya	Fremont, CA	Sales Rep	$80,000

如下示例在Employees表中檢索可得到的ID、Name和Salary列：

SQL> SELECT ID, NAME, SALARY FROM Employees where ID = 1;

若是用編程的方式，您必須建立如下代碼：

String selectSQL = 「SELECT ID, NAME FROM Employees WHERE ID = 1」 ;
Statement = dbConnection.createStatement() ;
ResultSet rs = Statement.executeQuery(selectSQL ) ;
while (rs.next())
{
String userid = rs.getString(「ID」) ;
String username = rs.getString(「NAME」) ;
}

可是，ORM的代碼爲：

Employee_list = EmployeeTable.query(ID=1) ;

如您所見，ORM簡化了複雜的代碼。除此以外，ORM還具備如下優勢：

• 數據模型在一個地方，節約時間。
• 便於代碼的更新、維護和從新使用。
• 使用您的首選編程語言，靈活性高。

固然，您必需要花點時間學習ORM。Hibernate (Java)、Propel或Doctrine (PHP)、Django或SQLAlchemy (Python)周圍有不少ORM。

本文重點討論Hibernate。Hibernate ORM (Hibernate)是一個Java的對象-關係映射框架，提供面向對象的域模型-傳統關係型數據庫的映射。Hibernate用高層級的對象處理函數替代直接的持久化相關數據庫訪問，解決了對象-關係的抗阻失配問題。Hibernate是自由軟件，符合GNU寬通用公共許可協議2.1。功能包括Java類-數據庫表的映射（和Java數據類型-SQL數據類型的映射）、數據查詢和檢索。Hibernate生成SQL調用，減輕開發人員的手動結果集處理和對象轉換。使用Hibernate的應用程序是很是輕便的，只需很小的性能開銷，便可支持SQL數據庫。

Hibernate位於傳統的Java對象和數據庫服務器之間，根據適當的O/R機制和模式，處理持久化這些對象的全部操做。

Hibernate採用分層架構，分離了底層的API。Hibernate利用數據庫和配置數據，嚮應用程序提供持久化服務（和持久對象）。下圖顯示了Hibernate的高層架構：

接下來，瞭解Trafodion如何支持Hibernate框架。若要支持Hibernate，數據庫的供應商必須建立一個方言，該方言要可以實現最佳性能、可以利用豐富的功能。有些功能/函數可能只在Trafodion（或其餘數據庫）中可用，不受Hibernate的支持。在這種狀況下，Hibernate SQL方言會將您的Hibernate應用程序翻譯成SQL語言，與您的數據庫進行通訊。咱們建立了一個Trafodion方言，若是遇到Hibernate應用程序，Hibernate將解析此類功能。Trafodion方言的JIRA：https://hibernate.atlassian.n...。

使用Trafodion方言的步驟和示例代碼

1.建立Trafodion數據庫表。

*SET SCHEMA TRAFODION.SEABASE;
DROP TABLE employee;
CREATE TABLE EMPLOYEE (
id INT NOT NULL ,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary INT default NULL,
PRIMARY KEY (id)
);
CREATE SEQUENCE trafodion.seabase.empseq;*

2.建立POJO類。

Employee.java的內容：

package trafodion.hibernate.common;
public class Employee {
private int id;
private String firstName;
private String lastName;
private int salary;
public Employee() {}
public Employee(String fname, String lname, int salary) {
this.firstName = fname;
this.lastName = lname;
this.salary = salary;
}
public int getId() {
return id;
}
public void setId( int id ) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName( String first_name ) {
this.firstName = first_name;
}
public String getLastName() {
return lastName;
}
public void setLastName( String last_name ) {
this.lastName = last_name;
}
public int getSalary() {
return salary;
}
public void setSalary( int salary ) {
this.salary = salary;
}
}

HibernateUtil.java的內容：

package trafodion.hibernate.persistence;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();
private static SessionFactory buildSessionFactory() {
try {
// Create the SessionFactory from hibernate.cfg.xml
return new Configuration().configure().buildSessionFactory();
}
catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
System.err.println(「Initial SessionFactory creation failed.」 + ex);
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
public static void shutdown() {
// Close caches and connection pools
getSessionFactory().close();
}
}

3.建立映射配置文件。

如下文件告訴Hibernate如何映射Java類型-數據庫表：

Employee.hbm.xml文件的內容：

「http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd」

該Java類包含員工的詳細信息：

trafodion.seabase.empseq

Trafodion數據庫的hibernate配置文件內容：

「-//Hibernate/Hibernate Configuration DTD 3.0//EN」
「http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd」>
false
org.trafodion.jdbc.t4.T4Driver
zz
jdbc:t4jdbc://10.12.10.21:12345/:
zz
org.hibernate.dialect.TrafodionDialect
true

4.建立應用程序類文件（ManageEmployee.java）。

package trafodion.hibernate.common;
import java.util.List;
import java.util.Date;
import java.util.Iterator;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class ManageEmployee {
  private static SessionFactory factory;
   public static void main(String[] args) {
      try{
         factory = new Configuration().configure().buildSessionFactory();
      }catch (Throwable ex) {
         System.err.println("Failed to create sessionFactory object." + ex);
         throw new ExceptionInInitializerError(ex);
      }
      ManageEmployee ME = new ManageEmployee();
      /* Add few employee records in database */
      Integer empID1 = ME.addEmployee("AAA", "Ali", 1000);
      Integer empID2 = ME.addEmployee("BBB", "Das", 5000);
      Integer empID3 = ME.addEmployee("CCC", "Paul", 10000);
      /* List down all the employees */
      ME.listEmployees();
      /* Update employee's records */
      ME.updateEmployee(empID1, 5000);
      /* List down all the employees */
      ME.listEmployees();
      /* Delete an employee from the database */
      ME.deleteEmployee(empID2);
      /* List down new list of the employees */
      ME.listEmployees();
   }
   /* Method to CREATE an employee in the database */
   public Integer addEmployee(String fname, String lname, int salary){
      Session session = factory.openSession();
      Transaction tx = null;
      Integer employeeID = null;
      try{
         tx = session.beginTransaction();
         Employee employee = new Employee(fname, lname, salary);
         employeeID = (Integer) session.save(employee);
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace();
      }finally {
         session.close();
      }
      return employeeID;
   }
   /* Method to  READ all the employees */
   public void listEmployees( ){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Query qry= session.createQuery("FROM Employee");
         List employees= qry.list();
         //List employees = session.createQuery("FROM Employee").list();
         for (Iterator iterator =
                    employees.iterator(); iterator.hasNext();){
            Employee employee = (Employee) iterator.next();
            System.out.print("First Name: " + employee.getFirstName());
            System.out.print("  Last Name: " + employee.getLastName());
            System.out.println("  Salary: " + employee.getSalary());
         }
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace();
      }finally {
         session.close();
      }
   }
   /* Method to UPDATE salary for an employee */
   public void updateEmployee(Integer EmployeeID, int salary ){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Employee employee =
            (Employee)session.get(Employee.class, EmployeeID);
         employee.setSalary( salary );
         session.update(employee);
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace();
      }finally {
         session.close();
      }
   }
   /* Method to DELETE an employee from the records */
   public void deleteEmployee(Integer EmployeeID){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Employee employee =
             (Employee)session.get(Employee.class, EmployeeID);
         session.delete(employee);
         tx.commit();
      }catch (HibernateException e) {
        if (tx!=null) tx.rollback();
         e.printStackTrace();
      }finally {
         session.close();
      }
   }
 }

致謝：感謝ADP首席數據科學家，Haifeng Li爲Trafodion方言做出的貢獻