Hibernate查詢語言（HQL）是一種物件導向的查詢語言，類似於SQL，但不是對錶和列操作，HQL適用於持久性物件和它們的屬性。 HQL查詢由Hibernate轉換成傳統的SQL查詢，這會在圈上的資料庫執行操作。
雖然可以直接使用SQL語句和Hibernate使用原生SQL，但建議使用HQL盡可能避免資料庫可移植性的麻煩，並採取Hibernate的SQL產生和快取策略的優勢。
都像SELECT，FROM和WHERE等關鍵字不區分大小寫，但如表名和列名的屬性是區分在HQL敏感。
FROM 語句
使用FROM子句，如果要載入一個完整的持久化物件到記憶體中。以下是使用FROM子句的簡單的語法：
String hql = "FROM Employee"; Query query = session.createQuery(hql); List results = query.list();
如果需要完全限定在HQL一個類別名，只需指定如下的套件和類別名稱：
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
String hql = "FROM Employee AS E"; Query query = session.createQuery(hql); List results = query.list();
AS子句可以用來別名分配給類別中的HQL查詢，特別是當有很長的查詢。例如，我們前面簡單的例子是以下幾點：
String hql = "FROM Employee E"; Query query = session.createQuery(hql); List results = query.list();
AS關鍵字是可選的，也可以直接在之後的類別名稱指定別名，如下所示：
String hql = "SELECT E.firstName FROM Employee E"; Query query = session.createQuery(hql); List results = query.list();
SELECT子句提供了更多的控制權比from子句的結果集。如果想要取得物件而不是整個物件的幾個屬性，使用SELECT子句。下面是使用SELECT語句來取得Employee物件只是FIRST_NAME欄位的簡單的語法：
String hql = "FROM Employee E WHERE E.id = 10"; Query query = session.createQuery(hql); List results = query.list();
如果想縮小了從儲存返回的特定對象，可以使用WHERE子句。以下是使用WHERE子句的簡單的語法：
String hql = "FROM Employee E WHERE E.id > 10 ORDER BY E.salary DESC"; Query query = session.createQuery(hql); List results = query.list();
若要排序HQL查詢的結果，將需要使用ORDER BY子句。您可以在結果集按升序（ASC）或降序（DESC）透過在物件的任何屬性排序結果。以下是一個使用ORDER BY子句的簡單的語法：
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();如果想透過一個以上的屬性進行排序，你會僅僅是額外的屬性添加到由子句用逗號隔開，如下所示的命令的結尾：
String hql = "SELECT SUM(E.salary), E.firtName FROM Employee E " +
"GROUP BY E.firstName";
Query query = session.createQuery(hql);
List results = query.list();該子句允許從Hibernate的它基於屬性的值的資料庫和群組提取訊息，並且通常使用結果包括總值。下面是一個使用GROUP BY子句的語法很簡單：
String hql = "FROM Employee E WHERE E.id = :employee_id";
Query query = session.createQuery(hql);
query.setParameter("employee_id",10);
List results = query.list();Hibernate命名在其HQL查詢參數支援。這使得編寫接受來自使用者的輸入容易，不必對SQL注入攻擊防禦HQL查詢。以下是使用命名參數的簡單的語法：
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);批次更新是新的HQL與Hibernate3，以及不同的刪除工作，在Hibernate 3和Hibernate2一樣。 Query介面現在包含一個名為executeUpdate()方法用來執行HQL UPDATE或DELETE語句。
在UPDATE子句可以用來更新一個或多個物件中的一個或多個屬性。以下是使用UPDATE子句的簡單的語法：
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);DELETE子句可以用來刪除一個或多個物件。下面是一個使用DELETE子句的簡單的語法：
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);HQL支援INSERT INTO子句中只記錄在那裡可以插入從一個物件到另一個物件。以下是使用INSERT INTO子句的簡單的語法：
String hql = "SELECT count(distinct E.firstName) FROM Employee E"; Query query = session.createQuery(hql); List results = query.list();
聚合方法
HQL支援多種聚合方法，類似於SQL。他們工作在HQL同樣的方式在SQL和下面的可用功能列表：DISTINCT關鍵字只計算在該行設定的唯一值。下面的查詢將只傳回唯一的計數：
String hql = "FROM Employee"; Query query = session.createQuery(hql); query.setFirstResult(1); query.setMaxResults(10); List results = query.list();
有兩個用於分頁查詢介面的方法。
Query setFirstResult(int startPosition)
Query setMaxResults(int maxResult)
採用上述兩種方法一起，可以在網站或Swing應用程式建立一個分頁元件。下面是例子，可以擴充來取得10行：
Criteria cr = session.createCriteria(Employee.class); List results = cr.list();
查詢條件
Hibernate提供了操作對象，並依序資料在RDBMS表可用的備用方式。其中一個方法是標準的API，它允許你建立一個標準的查詢物件編程，可以套用過濾規則和邏輯條件。Hibernate的Session介面提供了可用於建立一個傳回的持久化物件的類別的實例時，應用程式執行一個條件查詢一個Criteria物件createCriteria()方法。
以下是最簡單的一個條件查詢的範例是將簡單地傳回對應於Employee類別的每個物件。
Criteria cr = session.createCriteria(Employee.class);
cr.add(Restrictions.eq("salary", 2000));
List results = cr.list();可以使用add（）方法可用於Criteria物件新增限制條件查詢。以下是例子增加一個限制與薪水返回的記錄是等於2000：
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"));
可以创建AND或OR使用LogicalExpression限制如下条件：
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();以下是幾個例子覆蓋不同的場景，並且可以根據要求使用：
Criteria cr = session.createCriteria(Employee.class); cr.setFirstResult(1); cr.setMaxResults(10); List results = cr.list();
public Criteria setMaxResults(int maxResults)
采用上述两种方法一起，我们可以在我们的网站或Swing应用程序构建一个分页组件。下面是例子，可以扩展来每次获取10行：
Criteria cr = session.createCriteria(Employee.class); cr.setFirstResult(1); cr.setMaxResults(10); List results = cr.list();
排序的结果：
标准的API提供了org.hibernate.criterion.Order类排序按升序或降序排列你的结果集，根据对象的属性。这个例子演示了如何使用Order类的结果集进行排序：
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();预测与聚合：
该Criteria API提供了一个org.hibernate.criterion.Projections类可用于获取平均值，最大值或最小值的属性值。Projections类是类似于类限制，因为它提供了几个静态工厂方法用于获得Projection 实例。 provides the
以下是涉及不同的方案的一些例子，可按规定使用：
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 Queries 例子：
考虑下面的POJO类：
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;
}
}让我们创建下面的EMPLOYEE表来存储Employee对象：
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) );
以下将被映射文件。
<?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，我们将创建应用程序类的main（）方法来运行，我们将使用Criteria查询的应用程序：
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();
}
}
}编译和执行：
下面是步骤来编译并运行上述应用程序。请确保您已在进行的编译和执行之前，适当地设置PATH和CLASSPATH。
创建hibernate.cfg.xml配置文件中配置章节解释。
创建Employee.hbm.xml映射文件，如上图所示。
创建Employee.java源文件，如上图所示，并编译它。
创建ManageEmployee.java源文件，如上图所示，并编译它。
执行ManageEmployee二进制运行程序.
会得到以下结果，并记录将创建在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
如果检查EMPLOYEE表，它应该记录如下：
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)
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