Hibernate查詢語言(HQL)是一種面向對象的查詢語言,類似於SQL,但不是對表和列操作,HQL適用於持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盡可能避免數據庫可移植性的麻煩,並采取Hibernate的SQL生成和緩存策略的優勢。
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,如果要加載一個完整的持久化對象到內存中。下面是一個使用FROM子句的簡單的語法:
1 String hql = "FROM Employee";//Employee 是實體類名,嚴格區分大小寫 2 Query query = session.createQuery(hql); 3 List results = query.list();
如果需要完全限定在HQL一個類名,只需指定如下的包和類名:
1 String hql = "FROM com.shuyinghengxie.haha.Employee"; 2 Query query = session.createQuery(hql); 3 List results = query.list();
AS 語句
AS子句可以用來別名分配給類中的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 AS E"; Query query = session.createQuery(hql); List results = query.list();
AS關鍵字是可選的,也可以直接在之后的類名指定別名,如下所示:
1 String hql = "FROM Employee E"; 2 Query query = session.createQuery(hql); 3 List results = query.list();
SELECT 子句
SELECT子句提供了更多的控制權比from子句的結果集。如果想獲得對象而不是整個對象的幾個屬性,使用SELECT子句。下面是一個使用SELECT語句來獲取Employee對象只是FIRST_NAME字段的簡單的語法:
String hql = "SELECT E.firstName FROM Employee E"; Query query = session.createQuery(hql); List results = query.list();
值得注意的是在這里,Employee.firstName是Employee對象的一個屬性,而不是EMPLOYEE表的一個字段。
WHERE 子句
如果想縮小了從存儲返回的特定對象,可以使用WHERE子句。下面是一個使用WHERE子句的簡單的語法:
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)通過在對象的任何屬性排序結果。下面是一個使用ORDER BY子句的簡單的語法:
String hql = "FROM Employee E WHERE E.id > 10 ORDER BY E.salary DESC"; Query query = session.createQuery(hql); List results = query.list();
如果想通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 = "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
該子句允許從Hibernate的它基於屬性的值的數據庫和組提取信息,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 = "SELECT SUM(E.salary), E.firtName FROM Employee E " + "GROUP BY E.firstName"; Query query = session.createQuery(hql); List results = query.list();
使用命名參數
Hibernate命名在其HQL查詢參數支持。這使得編寫接受來自用戶的輸入容易,不必對SQL注入攻擊防御HQL查詢。下面是一個使用命名參數的簡單的語法:
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,以及不同的刪除工作,在Hibernate 3和Hibernate2一樣。 Query接口現在包含一個名為executeUpdate()方法用於執行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。下面是一個使用UPDATE子句的簡單的語法:
1 String hql = "UPDATE Employee set salary = :salary " + 2 "WHERE id = :employee_id"; 3 Query query = session.createQuery(hql); 4 query.setParameter("salary", 1000); 5 query.setParameter("employee_id", 10); 6 int result = query.executeUpdate(); 7 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。下面是一個使用DELETE子句的簡單的語法:
1 String hql = "DELETE FROM Employee " + 2 "WHERE id = :employee_id"; 3 Query query = session.createQuery(hql); 4 query.setParameter("employee_id", 10); 5 int result = query.executeUpdate(); 6 System.out.println("Rows affected: " + result);
INSERT 子句
HQL支持INSERT INTO子句中只記錄在那里可以插入從一個對象到另一個對象。以下是使用INSERT INTO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);
聚合方法
HQL支持多種聚合方法,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。下面的查詢將只返回唯一的計數:
1 String hql = "SELECT count(distinct E.firstName) FROM Employee E"; 2 Query query = session.createQuery(hql); 3 List results = query.list();
使用查詢分頁
有用於分頁查詢接口的兩個方法。
- Query setFirstResult(int startPosition)
- Query setMaxResults(int maxResult)
采用上述兩種方法一起,可以在網站或Swing應用程序構建一個分頁組件。下面是例子,可以擴展來獲取10行:
1 String hql = "FROM Employee"; 2 Query query = session.createQuery(hql); 3 query.setFirstResult(1); 4 query.setMaxResults(10); 5 List results = query.list();
查詢條件
Hibernate提供了操作對象,並依次數據在RDBMS表可用的備用方式。其中一個方法是標准的API,它允許你建立一個標准的查詢對象編程,可以套用過濾規則和邏輯條件。
Hibernate的Session接口提供了可用於創建一個返回的持久化對象的類的實例時,應用程序執行一個條件查詢一個Criteria對象createCriteria()方法。
以下是最簡單的一個條件查詢的例子是將簡單地返回對應於Employee類的每個對象。
Criteria cr = session.createCriteria(Employee.class); List results = cr.list();
限制與標准:
可以使用add()方法可用於Criteria對象添加限制條件查詢。下面是例子增加一個限制與薪水返回的記錄是等於2000:
1 Criteria cr = session.createCriteria(Employee.class); 2 cr.add(Restrictions.eq("salary", 2000)); 3 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:
1 Criteria cr = session.createCriteria(Employee.class); 2 3 // To get records having salary more than 2000 4 cr.add(Restrictions.gt("salary", 2000)); 5 6 // To get records having salary less than 2000 7 cr.add(Restrictions.lt("salary", 2000)); 8 9 // To get records having fistName starting with zara 10 cr.add(Restrictions.like("firstName", "zara%")); 11 12 // Case sensitive form of the above restriction. 13 cr.add(Restrictions.ilike("firstName", "zara%")); 14 15 // To get records having salary in between 1000 and 2000 16 cr.add(Restrictions.between("salary", 1000, 2000)); 17 18 // To check if the given property is null 19 cr.add(Restrictions.isNull("salary")); 20 21 // To check if the given property is not null 22 cr.add(Restrictions.isNotNull("salary")); 23 24 // To check if the given property is empty 25 cr.add(Restrictions.isEmpty("salary")); 26 27 // To check if the given property is not empty 28 cr.add(Restrictions.isNotEmpty("salary")); 29 可以創建AND或OR使用LogicalExpression限制如下條件: 30 31 Criteria cr = session.createCriteria(Employee.class); 32 33 Criterion salary = Restrictions.gt("salary", 2000); 34 Criterion name = Restrictions.ilike("firstNname","zara%"); 35 36 // To get records matching with OR condistions 37 LogicalExpression orExp = Restrictions.or(salary, name); 38 cr.add( orExp ); 39 40 41 // To get records matching with AND condistions 42 LogicalExpression andExp = Restrictions.and(salary, name); 43 cr.add( andExp ); 44 45 List results = cr.list();
雖然上述所有條件,可以直接使用HQL在前面的教程中介紹。
分頁使用標准:
還有的標准接口,用於分頁的兩種方法。
- public Criteria setFirstResult(int firstResult)
- public Criteria setMaxResults(int maxResults)
采用上述兩種方法一起,我們可以在我們的網站或Swing應用程序構建一個分頁組件。下面是例子,可以擴展來每次獲取10行:
1 Criteria cr = session.createCriteria(Employee.class); 2 cr.setFirstResult(1); 3 cr.setMaxResults(10); 4 List results = cr.list();
排序的結果:
標准的API提供了org.hibernate.criterion.Order類排序按升序或降序排列你的結果集,根據對象的屬性。這個例子演示了如何使用Order類的結果集進行排序:
1 Criteria cr = session.createCriteria(Employee.class); 2 // To get records having salary more than 2000 3 cr.add(Restrictions.gt("salary", 2000)); 4 5 // To sort records in descening order 6 crit.addOrder(Order.desc("salary")); 7 8 // To sort records in ascending order 9 crit.addOrder(Order.asc("salary")); 10 11 List results = cr.list();
預測與聚合:
該Criteria API提供了一個org.hibernate.criterion.Projections類可用於獲取平均值,最大值或最小值的屬性值。Projections類是類似於類限制,因為它提供了幾個靜態工廠方法用於獲得Projection 實例。 provides the
以下是涉及不同的方案的一些例子,可按規定使用:
1 Criteria cr = session.createCriteria(Employee.class); 2 3 // To get total row count. 4 cr.setProjection(Projections.rowCount()); 5 6 // To get average of a property. 7 cr.setProjection(Projections.avg("salary")); 8 9 // To get distinct count of a property. 10 cr.setProjection(Projections.countDistinct("firstName")); 11 12 // To get maximum of a property. 13 cr.setProjection(Projections.max("salary")); 14 15 // To get minimum of a property. 16 cr.setProjection(Projections.min("salary")); 17 18 // To get sum of a property. 19 cr.setProjection(Projections.sum("salary"));
Criteria Queries 例子:
考慮下面的POJO類:
1 public class Employee { 2 private int id; 3 private String firstName; 4 private String lastName; 5 private int salary; 6 7 public Employee() {} 8 public Employee(String fname, String lname, int salary) { 9 this.firstName = fname; 10 this.lastName = lname; 11 this.salary = salary; 12 } 13 public int getId() { 14 return id; 15 } 16 public void setId( int id ) { 17 this.id = id; 18 } 19 public String getFirstName() { 20 return firstName; 21 } 22 public void setFirstName( String first_name ) { 23 this.firstName = first_name; 24 } 25 public String getLastName() { 26 return lastName; 27 } 28 public void setLastName( String last_name ) { 29 this.lastName = last_name; 30 } 31 public int getSalary() { 32 return salary; 33 } 34 public void setSalary( int salary ) { 35 this.salary = salary; 36 } 37 }
讓我們創建下面的EMPLOYEE表來存儲Employee對象:
1 create table EMPLOYEE ( 2 id INT NOT NULL auto_increment, 3 first_name VARCHAR(20) default NULL, 4 last_name VARCHAR(20) default NULL, 5 salary INT default NULL, 6 PRIMARY KEY (id) 7 );
以下將被映射文件
1 <?xml version="1.0" encoding="utf-8"?> 2 <!DOCTYPE hibernate-mapping PUBLIC 3 "-//Hibernate/Hibernate Mapping DTD//EN" 4 "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> 5 6 <hibernate-mapping> 7 <class name="Employee" table="EMPLOYEE"> 8 <meta attribute="class-description"> 9 This class contains the employee detail. 10 </meta> 11 <id name="id" type="int" column="id"> 12 <generator class="native"/> 13 </id> 14 <property name="firstName" column="first_name" type="string"/> 15 <property name="lastName" column="last_name" type="string"/> 16 <property name="salary" column="salary" type="int"/> 17 </class> 18 </hibernate-mapping>
最后,我們將創建應用程序類的main()方法來運行,我們將使用Criteria查詢的應用程序:
1 import java.util.List; 2 import java.util.Date; 3 import java.util.Iterator; 4 5 import org.hibernate.HibernateException; 6 import org.hibernate.Session; 7 import org.hibernate.Transaction; 8 import org.hibernate.SessionFactory; 9 import org.hibernate.Criteria; 10 import org.hibernate.criterion.Restrictions; 11 import org.hibernate.criterion.Projections; 12 import org.hibernate.cfg.Configuration; 13 14 public class ManageEmployee { 15 private static SessionFactory factory; 16 public static void main(String[] args) { 17 try{ 18 factory = new Configuration().configure().buildSessionFactory(); 19 }catch (Throwable ex) { 20 System.err.println("Failed to create sessionFactory object." + ex); 21 throw new ExceptionInInitializerError(ex); 22 } 23 ManageEmployee ME = new ManageEmployee(); 24 25 /* Add few employee records in database */ 26 Integer empID1 = ME.addEmployee("Zara", "Ali", 2000); 27 Integer empID2 = ME.addEmployee("Daisy", "Das", 5000); 28 Integer empID3 = ME.addEmployee("John", "Paul", 5000); 29 Integer empID4 = ME.addEmployee("Mohd", "Yasee", 3000); 30 31 /* List down all the employees */ 32 ME.listEmployees(); 33 34 /* Print Total employee's count */ 35 ME.countEmployee(); 36 37 /* Print Toatl salary */ 38 ME.totalSalary(); 39 } 40 /* Method to CREATE an employee in the database */ 41 public Integer addEmployee(String fname, String lname, int salary){ 42 Session session = factory.openSession(); 43 Transaction tx = null; 44 Integer employeeID = null; 45 try{ 46 tx = session.beginTransaction(); 47 Employee employee = new Employee(fname, lname, salary); 48 employeeID = (Integer) session.save(employee); 49 tx.commit(); 50 }catch (HibernateException e) { 51 if (tx!=null) tx.rollback(); 52 e.printStackTrace(); 53 }finally { 54 session.close(); 55 } 56 return employeeID; 57 } 58 59 /* Method to READ all the employees having salary more than 2000 */ 60 public void listEmployees( ){ 61 Session session = factory.openSession(); 62 Transaction tx = null; 63 try{ 64 tx = session.beginTransaction(); 65 Criteria cr = session.createCriteria(Employee.class); 66 // Add restriction. 67 cr.add(Restrictions.gt("salary", 2000)); 68 List employees = cr.list(); 69 70 for (Iterator iterator = 71 employees.iterator(); iterator.hasNext();){ 72 Employee employee = (Employee) iterator.next(); 73 System.out.print("First Name: " + employee.getFirstName()); 74 System.out.print(" Last Name: " + employee.getLastName()); 75 System.out.println(" Salary: " + employee.getSalary()); 76 } 77 tx.commit(); 78 }catch (HibernateException e) { 79 if (tx!=null) tx.rollback(); 80 e.printStackTrace(); 81 }finally { 82 session.close(); 83 } 84 } 85 /* Method to print total number of records */ 86 public void countEmployee(){ 87 Session session = factory.openSession(); 88 Transaction tx = null; 89 try{ 90 tx = session.beginTransaction(); 91 Criteria cr = session.createCriteria(Employee.class); 92 93 // To get total row count. 94 cr.setProjection(Projections.rowCount()); 95 List rowCount = cr.list(); 96 97 System.out.println("Total Coint: " + rowCount.get(0) ); 98 tx.commit(); 99 }catch (HibernateException e) { 100 if (tx!=null) tx.rollback(); 101 e.printStackTrace(); 102 }finally { 103 session.close(); 104 } 105 } 106 /* Method to print sum of salaries */ 107 public void totalSalary(){ 108 Session session = factory.openSession(); 109 Transaction tx = null; 110 try{ 111 tx = session.beginTransaction(); 112 Criteria cr = session.createCriteria(Employee.class); 113 114 // To get total salary. 115 cr.setProjection(Projections.sum("salary")); 116 List totalSalary = cr.list(); 117 118 System.out.println("Total Salary: " + totalSalary.get(0) ); 119 tx.commit(); 120 }catch (HibernateException e) { 121 if (tx!=null) tx.rollback(); 122 e.printStackTrace(); 123 }finally { 124 session.close(); 125 } 126 } 127 }
編譯和執行:
下面是步驟來編譯並運行上述應用程序。請確保您已在進行的編譯和執行之前,適當地設置PATH和CLASSPATH。
- 創建hibernate.cfg.xml配置文件中配置章節解釋。
- 創建Employee.hbm.xml映射文件,如上圖所示。
- 創建Employee.java源文件,如上圖所示,並編譯它。
- 創建ManageEmployee.java源文件,如上圖所示,並編譯它。
- 執行ManageEmployee二進制運行程序.
會得到以下結果,並記錄將創建在EMPLOYEE表中。
轉自http://www.jb51.net/article/76764.htm