Hibernate 查詢語句


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 


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