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在Java的Hibernate框架中對數據庫數據停止查詢操作

編輯：關於JAVA

在Java的Hibernate框架中對數據庫數據停止查詢操作。本站提示廣大學習愛好者：（在Java的Hibernate框架中對數據庫數據停止查詢操作）文章只能為提供參考，不一定能成為您想要的結果。以下是在Java的Hibernate框架中對數據庫數據停止查詢操作正文

Hibernate查詢說話（HQL）是一種面向對象的查詢說話，相似於SQL，但不是對表和列操作，HQL實用於耐久對象和它們的屬性。 HQL查詢由Hibernate轉換成傳統的SQL查詢，這在圈上的數據庫履行操作。

固然可以直接應用SQL語句和Hibernate應用原生SQL，但建議應用HQL盡量防止數據庫可移植性的費事，並采用Hibernate的SQL生成懈弛存戰略的優勢。

都像SELECT，FROM和WHERE等症結字不辨別年夜小寫，但如表名和列名的屬性是辨別在HQL敏感。

FROM 語句
應用FROM子句，假如要加載一個完全的耐久化對象到內存中。上面是一個應用FROM子句的簡略的語法：

String hql = "FROM Employee";
Query query = session.createQuery(hql);
List results = query.list();

假如須要完整限制在HQL一個類名，只需指定以下的包和類名：

String hql = "FROM com.hibernatebook.criteria.Employee";
Query query = session.createQuery(hql);
List results = query.list();

AS 語句
AS子句可以用來別號分派給類中的HQL查詢，特殊是當有很長的查詢。例如，我們後面簡略的例子是以下幾點：

String hql = "FROM Employee AS E";
Query query = session.createQuery(hql);
List results = query.list();

AS症結字是可選的，也能夠直接在以後的類名指定別號，以下所示：

String hql = "FROM Employee E";
Query query = session.createQuery(hql);
List results = query.list();

SELECT 子句
SELECT子句供給了更多的掌握權比from子句的成果集。假如想取得對象而不是全部對象的幾個屬性，應用SELECT子句。上面是一個應用SELECT語句來獲得Employee對象只是FIRST_NAME字段的簡略的語法：

String hql = "SELECT E.firstName FROM Employee E";
Query query = session.createQuery(hql);
List results = query.list();

值得留意的是在這裡，Employee.firstName是Employee對象的一個屬性，而不是EMPLOYEE表的一個字段。

WHERE 子句
假如想減少了從存儲前往的特定對象，可使用WHERE子句。上面是一個應用WHERE子句的簡略的語法：

String hql = "FROM Employee E WHERE E.id = 10";
Query query = session.createQuery(hql);
List results = query.list();

ORDER BY 子句
若要排序HQL查詢的成果，將須要應用ORDER BY子句。您可以在成果集按升序（ASC）或降序（DESC）經由過程在對象的任何屬性排序成果。上面是一個應用ORDER BY子句的簡略的語法：

String hql = "FROM Employee E WHERE E.id > 10 ORDER BY E.salary DESC";
Query query = session.createQuery(hql);
List results = query.list();

假如想經由過程一個以上的屬性停止排序，你會僅僅是額定的屬性添加到由子句用逗號離隔，以下所示的敕令的開頭：

String hql = "FROM Employee E WHERE E.id > 10 " +
       "ORDER BY E.firstName DESC, E.salary DESC ";
Query query = session.createQuery(hql);
List results = query.list();

GROUP BY 子句
該子句許可從Hibernate的它基於屬性的值的數據庫和組提守信息，而且平日應用成果包含總值。上面是一個應用GROUP BY子句的語法很簡略：

String hql = "SELECT SUM(E.salary), E.firtName FROM Employee E " +
       "GROUP BY E.firstName";
Query query = session.createQuery(hql);
List results = query.list();

應用定名參數
Hibernate定名在其HQL查詢參數支撐。這使得編寫接收來自用戶的輸出輕易，不用對SQL注入進擊進攻HQL查詢。上面是一個應用定名參數的簡略的語法：

String hql = "FROM Employee E WHERE E.id = :employee_id";
Query query = session.createQuery(hql);
query.setParameter("employee_id",10);
List results = query.list();

UPDATE 子句
批量更新是新的HQL與Hibernate3，和分歧的刪除任務，在Hibernate 3和Hibernate2一樣。 Query接口如今包括一個名為executeUpdate()辦法用於履行HQL UPDATE或DELETE語句。

在UPDATE子句可以用於更新一個或多個對象中的一個或多個屬性。上面是一個應用UPDATE子句的簡略的語法：

String hql = "UPDATE Employee set salary = :salary " + 
       "WHERE id = :employee_id";
Query query = session.createQuery(hql);
query.setParameter("salary", 1000);
query.setParameter("employee_id", 10);
int result = query.executeUpdate();
System.out.println("Rows affected: " + result);

DELETE 子句
DELETE子句可以用來刪除一個或多個對象。上面是一個應用DELETE子句的簡略的語法：

String hql = "DELETE FROM Employee " + 
       "WHERE id = :employee_id";
Query query = session.createQuery(hql);
query.setParameter("employee_id", 10);
int result = query.executeUpdate();
System.out.println("Rows affected: " + result);

INSERT 子句
HQL支撐INSERT INTO子句中只記載在那邊可以拔出從一個對象到另外一個對象。以下是應用INSERT INTO子句的簡略的語法：

String hql = "INSERT INTO Employee(firstName, lastName, salary)" + 
       "SELECT firstName, lastName, salary FROM old_employee";
Query query = session.createQuery(hql);
int result = query.executeUpdate();
System.out.println("Rows affected: " + result);

聚合辦法
HQL支撐多種聚合辦法，相似於SQL。他們任務在HQL異樣的方法在SQL和上面的可用功效列表：

DISTINCT症結字只盤算在該行設定的獨一值。上面的查詢將只前往獨一的計數：

String hql = "SELECT count(distinct E.firstName) FROM Employee E";
Query query = session.createQuery(hql);
List results = query.list();

應用查詢分頁
有效於分頁查詢接口的兩個辦法。

Query setFirstResult(int startPosition)
Query setMaxResults(int maxResult)

采取上述兩種辦法一路，可以在網站或Swing運用法式構建一個分頁組件。上面是例子，可以擴大來獲得10行：

String hql = "FROM Employee";
Query query = session.createQuery(hql);
query.setFirstResult(1);
query.setMaxResults(10);
List results = query.list();

查詢前提
Hibernate供給了操尴尬刁難象，並順次數據在RDBMS表可用的備用方法。個中一個辦法是尺度的API，它許可你樹立一個尺度的查詢對象編程，可以套用過濾規矩和邏輯前提。
Hibernate的Session接口供給了可用於創立一個前往的耐久化對象的類的實例時，運用法式履行一個前提查詢一個Criteria對象createCriteria()辦法。

以下是最簡略的一個前提查詢的例子是將簡略地前往對應於Employee類的每一個對象。

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

限制與尺度：
可使用add（）辦法可用於Criteria對象添加限制前提查詢。上面是例子增長一個限制與薪水前往的記載是等於2000：

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

以下是幾個例子籠罩分歧的場景，而且可以依據請求應用：

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"));
可以創立AND或OR應用LogicalExpression限制以下前提：

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();

固然上述一切前提，可以直接應用HQL在後面的教程中引見。

分頁應用尺度：
還有的尺度接口，用於分頁的兩種辦法。

public Criteria setFirstResult(int firstResult)
public Criteria setMaxResults(int maxResults)

采取上述兩種辦法一路，我們可以在我們的網站或Swing運用法式構建一個分頁組件。上面是例子，可以擴大來每次獲得10行：

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

排序的成果：
尺度的API供給了org.hibernate.criterion.Order類排序按升序或降序分列你的成果集，依據對象的屬性。這個例子演示了若何應用Order類的成果集停止排序：

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();

猜測與聚合：
該Criteria API供給了一個org.hibernate.criterion.Projections類可用於獲得均勻值，最年夜值或最小值的屬性值。Projections類是相似於類限制，由於它供給了幾個靜態工場辦法用於取得Projection 實例。 provides the

以下是觸及分歧的計劃的一些例子，可按劃定應用：

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 Queries 例子：
斟酌上面的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;
  }
}

讓我們創立上面的EMPLOYEE表來存儲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)
);

以下將被映照文件。

<?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>

最初，我們將創立運用法式類的main（）辦法來運轉，我們將應用Criteria查詢的運用法式：

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(); 
   }
  }
}

編譯和履行：
上面是步調來編譯並運轉上述運用法式。請確保您已在停止的編譯和履行之前，恰當地設置PATH和CLASSPATH。

創立hibernate.cfg.xml設置裝備擺設文件中設置裝備擺設章節說明。
創立Employee.hbm.xml映照文件，如上圖所示。
創立Employee.java源文件，如上圖所示，並編譯它。
創立ManageEmployee.java源文件，如上圖所示，並編譯它。
履行ManageEmployee二進制運轉法式.

會獲得以下成果，並記載將創立在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

假如檢討EMPLOYEE表，它應當記載以下：

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)