Hibernate - Criteria 查詢

上一頁
下一頁

Hibernate 提供了操作物件以及 RDBMS 表中資料的替代方法。其中一種方法是 Criteria API，它允許您以程式設計方式構建 Criteria 查詢物件，您可以在其中應用過濾規則和邏輯條件。

Hibernate 的 Session 介面提供了 createCriteria() 方法，該方法可用於建立一個 Criteria 物件，當您的應用程式執行 Criteria 查詢時，該物件將返回持久化物件類的例項。

以下是最簡單的 Criteria 查詢示例，它將簡單地返回與 Employee 類對應的每個物件。

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

Criteria 的限制條件

您可以使用 Criteria 物件可用的 add() 方法為 Criteria 查詢新增限制條件。以下是如何新增限制條件以返回薪資等於 2000 的記錄的示例 -

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

以下是一些涵蓋不同場景的示例，可以根據需要使用 -

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"));

您可以使用 LogicalExpression 限制條件建立 AND 或 OR 條件，如下所示 -

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

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

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

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

List results = cr.list();

儘管所有上述條件都可以直接與 HQL 一起使用，如前面教程中所述。

使用 Criteria 進行分頁

Criteria 介面有兩種分頁方法。

序號 方法和描述
1

public Criteria setFirstResult(int firstResult)

此方法接受一個整數，表示結果集中第一行的索引，從第 0 行開始。
2

public Criteria setMaxResults(int maxResults)

此方法告訴 Hibernate 檢索固定數量的 maxResults 物件。

將以上兩種方法結合使用，我們可以在 Web 或 Swing 應用程式中構建分頁元件。以下是一個示例，您可以將其擴充套件為一次獲取 10 行 -

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

排序結果

Criteria API 提供了 org.hibernate.criterion.Order 類，用於根據物件的某個屬性以升序或降序對結果集進行排序。此示例演示瞭如何使用 Order 類對結果集進行排序 -

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
cr.addOrder(Order.desc("salary"));

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

List results = cr.list();

投影和聚合

Criteria API 提供了 org.hibernate.criterion.Projections 類，該類可用於獲取屬性值的平均值、最大值或最小值。Projections 類類似於 Restrictions 類，因為它提供了多個靜態工廠方法來獲取 Projection 例項。

以下是一些涵蓋不同場景的示例，可以根據需要使用 -

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"));

Criteria 查詢示例

考慮以下 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;
   }
}

讓我們建立以下 EMPLOYEE 表來儲存 Employee 物件 -

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)
);

以下將是對映檔案。

<?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>

最後，我們將建立包含 main() 方法的應用程式類來執行應用程式，在其中我們將使用 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 Total 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(); 
      }
   }
}

編譯和執行

以下是編譯和執行上述應用程式的步驟。在繼續編譯和執行之前，請確保已正確設定 PATH 和 CLASSPATH。

  • 建立 hibernate.cfg.xml 配置檔案，如配置章節中所述。

  • 建立 Employee.hbm.xml 對映檔案，如上所示。

  • 建立 Employee.java 原始檔，如上所示，並進行編譯。

  • 建立 ManageEmployee.java 原始檔，如上所示，並進行編譯。

  • 執行 ManageEmployee 二進位制檔案以執行程式。

您將獲得以下結果，並且記錄將被建立到 EMPLOYEE 表中。

$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

如果您檢查 EMPLOYEE 表，它應該包含以下記錄 -

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>
列印頁面
上一頁
下一頁
廣告

© . All rights reserved.