Hibernate 標(biāo)準(zhǔn)查詢

標(biāo)準(zhǔn)查詢

Hibernate 提供了操縱對象和相應(yīng)的 RDBMS 表中可用的數(shù)據(jù)的替代方法。一種方法是標(biāo)準(zhǔn)的 API，它允許你建立一個(gè)標(biāo)準(zhǔn)的可編程查詢對象來應(yīng)用過濾規(guī)則和邏輯條件。

Hibernate Session 接口提供了 createCriteria() 方法，可用于創(chuàng)建一個(gè) Criteria 對象，使當(dāng)您的應(yīng)用程序執(zhí)行一個(gè)標(biāo)準(zhǔn)查詢時(shí)返回一個(gè)持久化對象的類的實(shí)例。

以下是一個(gè)最簡單的標(biāo)準(zhǔn)查詢的例子，它只是簡單地返回對應(yīng)于員工類的每個(gè)對象：

Criteria cr = session.createCriteria(Employee.class);  
List results = cr.list();  

對標(biāo)準(zhǔn)的限制

你可以使用 Criteria 對象可用的 add() 方法去添加一個(gè)標(biāo)準(zhǔn)查詢的限制。

以下是一個(gè)示例，它實(shí)現(xiàn)了添加一個(gè)限制，令返回工資等于 2000 的記錄：

Criteria cr = session.createCriteria(Employee.class);    
cr.add(Restrictions.eq("salary", 2000));    
List results = cr.list();  

以下是幾個(gè)例子，涵蓋了不同的情況，可按要求進(jìn)行使用：

Criteria cr = session.createCriteria(Employee.class);

// To get records having salary more than 2000
cr.add(Restrictions.gt("salary", 2000));

// To get records having salary less than 2000
cr.add(Restrictions.lt("salary", 2000));

// To get records having fistName starting with zara
cr.add(Restrictions.like("firstName", "zara%"));

// Case sensitive form of the above restriction.
cr.add(Restrictions.ilike("firstName", "zara%"));

// To get records having salary in between 1000 and 2000
cr.add(Restrictions.between("salary", 1000, 2000));

// To check if the given property is null
cr.add(Restrictions.isNull("salary"));

// To check if the given property is not null
cr.add(Restrictions.isNotNull("salary"));

// To check if the given property is empty
cr.add(Restrictions.isEmpty("salary"));

// To check if the given property is not empty
cr.add(Restrictions.isNotEmpty("salary"));

你可以模仿以下示例，使用邏輯表達(dá)式創(chuàng)建 AND 或 OR 的條件組合：

Criteria cr = session.createCriteria(Employee.class);

Criterion salary = Restrictions.gt("salary", 2000);
Criterion name = Restrictions.ilike("firstNname","zara%");

// To get records matching with OR condistions
LogicalExpression orExp = Restrictions.or(salary, name);
cr.add( orExp );

// To get records matching with AND condistions
LogicalExpression andExp = Restrictions.and(salary, name);
cr.add( andExp );

List results = cr.list();

另外，上述所有的條件都可按之前的教程中解釋的那樣與 HQL 直接使用。

分頁使用標(biāo)準(zhǔn)

這里有兩種分頁標(biāo)準(zhǔn)接口方法：

利用上述兩種方法結(jié)合在一起，我們可以在我們的 Web 或 Swing 應(yīng)用程序構(gòu)建一個(gè)分頁組件。以下是一個(gè)例子，利用它你可以一次取出 10 行：

Criteria cr = session.createCriteria(Employee.class);
cr.setFirstResult(1);
cr.setMaxResults(10);
List results = cr.list();

排序結(jié)果

標(biāo)準(zhǔn) API 提供了 org.hibernate.criterion.order 類可以去根據(jù)你的一個(gè)對象的屬性把你的排序結(jié)果集按升序或降序排列。這個(gè)例子演示了如何使用 Order 類對結(jié)果集進(jìn)行排序：

Criteria cr = session.createCriteria(Employee.class);
// To get records having salary more than 2000
cr.add(Restrictions.gt("salary", 2000));

// To sort records in descening order
crit.addOrder(Order.desc("salary"));

// To sort records in ascending order
crit.addOrder(Order.asc("salary"));

List results = cr.list();  

預(yù)測與聚合

標(biāo)準(zhǔn) API 提供了 org.hibernate.criterion.projections 類可得到各屬性值的平均值，最大值或最小值。Projections 類與 Restrictions 類相似，均提供了幾個(gè)獲取預(yù)測實(shí)例的靜態(tài)工廠方法。

以下是幾個(gè)例子，涵蓋了不同的情況，可按要求進(jìn)行使用：

Criteria cr = session.createCriteria(Employee.class);

// To get total row count.
cr.setProjection(Projections.rowCount());

// To get average of a property.
cr.setProjection(Projections.avg("salary"));

// To get distinct count of a property.
cr.setProjection(Projections.countDistinct("firstName"));

// To get maximum of a property.
cr.setProjection(Projections.max("salary"));

// To get minimum of a property.
cr.setProjection(Projections.min("salary"));

// To get sum of a property.
cr.setProjection(Projections.sum("salary"));  

標(biāo)準(zhǔn)查詢示例

考慮下面的 POJO 類：

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;
   }
}

讓我們創(chuàng)建以下員工表來存儲(chǔ) Employee 對象：

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)
);

以下是映射文件：

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
 "-//Hibernate/Hibernate Mapping DTD//EN"
 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 

<hibernate-mapping>
   <class name="Employee" table="EMPLOYEE">
      <meta attribute="class-description">
         This class contains the employee detail. 
      </meta>
      <id name="id" type="int" column="id">
         <generator class="native"/>
      </id>
      <property name="firstName" column="first_name" type="string"/>
      <property name="lastName" column="last_name" type="string"/>
      <property name="salary" column="salary" type="int"/>
   </class>
</hibernate-mapping>  

最后，我們將用 main() 方法創(chuàng)建應(yīng)用程序類來運(yùn)行應(yīng)用程序，我們將使用 Criteria 查詢：

import java.util.List; 
import java.util.Date;
import java.util.Iterator; 

import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.Criteria;
import org.hibernate.criterion.Restrictions;
import org.hibernate.criterion.Projections;
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("Zara", "Ali", 2000);
      Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
      Integer empID3 = ME.addEmployee("John", "Paul", 5000);
      Integer empID4 = ME.addEmployee("Mohd", "Yasee", 3000);

      /* List down all the employees */
      ME.listEmployees();

      /* Print Total employee's count */
      ME.countEmployee();

      /* Print Toatl salary */
      ME.totalSalary();
   }
   /* 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 having salary more than 2000 */
   public void listEmployees( ){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Criteria cr = session.createCriteria(Employee.class);
         // Add restriction.
         cr.add(Restrictions.gt("salary", 2000));
         List employees = cr.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 print total number of records */
   public void countEmployee(){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Criteria cr = session.createCriteria(Employee.class);

         // To get total row count.
         cr.setProjection(Projections.rowCount());
         List rowCount = cr.list();

         System.out.println("Total Coint: " + rowCount.get(0) );
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
   }
  /* Method to print sum of salaries */
   public void totalSalary(){
      Session session = factory.openSession();
      Transaction tx = null;
      try{
         tx = session.beginTransaction();
         Criteria cr = session.createCriteria(Employee.class);

         // To get total salary.
         cr.setProjection(Projections.sum("salary"));
         List totalSalary = cr.list();

         System.out.println("Total Salary: " + totalSalary.get(0) );
         tx.commit();
      }catch (HibernateException e) {
         if (tx!=null) tx.rollback();
         e.printStackTrace(); 
      }finally {
         session.close(); 
      }
   }
}  

編譯和執(zhí)行

這是編譯并運(yùn)行上述應(yīng)用程序的步驟。確保你有適當(dāng)?shù)?PATH 和 CLASSPATH，然后執(zhí)行編譯程序。

• 按照在配置一章講述的方法創(chuàng)建 hibernate.cfg.xml 配置文件。
• 如上述所示創(chuàng)建 employee.hbm.xml 映射文件。
• 如上述所示創(chuàng)建 employee.java 源文件并編譯。
• 如上述所示創(chuàng)建 manageemployee.java 源文件并編譯。
• 執(zhí)行 manageemployee 二進(jìn)制代碼運(yùn)行程序。

你會(huì)得到下面的結(jié)果，并且記錄將會(huì)在 EMPLOYEE 表創(chuàng)建。

$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........

First Name: Daisy  Last Name: Das  Salary: 5000
First Name: John  Last Name: Paul  Salary: 5000
First Name: Mohd  Last Name: Yasee  Salary: 3000
Total Coint: 4
Total Salary: 15000

如果你檢查你的 EMPLOYEE 表，它應(yīng)該有以下記錄：

mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 14 | Zara       | Ali       |   2000 |
| 15 | Daisy      | Das       |   5000 |
| 16 | John       | Paul      |   5000 |
| 17 | Mohd       | Yasee     |   3000 |
+----+------------+-----------+--------+
4 rows in set (0.00 sec)
mysql>