Hibernate 查询语句

Hibernate查询语言(HQL)是一种面向对象的查询语言,类似于SQL,但不是对表和列操作,HQL适用于持久对象和它们的属性。 HQL查询由Hibernate转换成传统的SQL查询,这在圈上的数据库执行操作。

虽然可以直接使用SQL语句和Hibernate使用原生SQL,但建议使用HQL尽可能避免数据库可移植性的麻烦,并采取Hibernate的SQL生成和缓存策略的优势。

都像SELECT,FROM和WHERE等关键字不区分大小写,但如表名和列名的属性是区分在HQL敏感。

FROM 语句
使用FROM子句,如果要加载一个完整的持久化对象到内存中。下面是一个使用FROM子句的简单的语法:

1 String hql = "FROM Employee";//Employee 是实体类名,严格区分大小写
2 Query query = session.createQuery(hql);
3 List results = query.list();

如果需要完全限定在HQL一个类名,只需指定如下的包和类名:

1 String hql = "FROM com.shuyinghengxie.haha.Employee";
2 Query query = session.createQuery(hql);
3 List results = query.list();

AS 语句
AS子句可以用来别名分配给类中的HQL查询,特别是当有很长的查询。例如,我们前面简单的例子是以下几点:

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

AS关键字是可选的,也可以直接在之后的类名指定别名,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权比from子句的结果集。如果想获得对象而不是整个对象的几个属性,使用SELECT子句。下面是一个使用SELECT语句来获取Employee对象只是FIRST_NAME字段的简单的语法:

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

值得注意的是在这里,Employee.firstName是Employee对象的一个属性,而不是EMPLOYEE表的一个字段。

WHERE 子句
如果想缩小了从存储返回的特定对象,可以使用WHERE子句。下面是一个使用WHERE子句的简单的语法:

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查询的结果,将需要使用ORDER BY子句。您可以在结果集按升序(ASC)或降序(DESC)通过在对象的任何属性排序结果。下面是一个使用ORDER BY子句的简单的语法:

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

如果想通过一个以上的属性进行排序,你会仅仅是额外的属性添加到由子句用逗号隔开,如下所示的命令的结尾:

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
该子句允许从Hibernate的它基于属性的值的数据库和组提取信息,并且通常使用结果包括总值。下面是一个使用GROUP BY子句的语法很简单:

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

使用命名参数
Hibernate命名在其HQL查询参数支持。这使得编写接受来自用户的输入容易,不必对SQL注入攻击防御HQL查询。下面是一个使用命名参数的简单的语法:

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与Hibernate3,以及不同的删除工作,在Hibernate 3和Hibernate2一样。 Query接口现在包含一个名为executeUpdate()方法用于执行HQL UPDATE或DELETE语句。

在UPDATE子句可以用于更新一个或多个对象中的一个或多个属性。下面是一个使用UPDATE子句的简单的语法:

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子句可以用来删除一个或多个对象。下面是一个使用DELETE子句的简单的语法:

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子句中只记录在那里可以插入从一个对象到另一个对象。以下是使用INSERT INTO子句的简单的语法:

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支持多种聚合方法,类似于SQL。他们工作在HQL同样的方式在SQL和下面的可用功能列表:

DISTINCT关键字只计算在该行设定的唯一值。下面的查询将只返回唯一的计数:

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

使用查询分页
有用于分页查询接口的两个方法。

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

采用上述两种方法一起,可以在网站或Swing应用程序构建一个分页组件。下面是例子,可以扩展来获取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();

查询条件
Hibernate提供了操作对象,并依次数据在RDBMS表可用的备用方式。其中一个方法是标准的API,它允许你建立一个标准的查询对象编程,可以套用过滤规则和逻辑条件。
Hibernate的Session接口提供了可用于创建一个返回的持久化对象的类的实例时,应用程序执行一个条件查询一个Criteria对象createCriteria()方法。

以下是最简单的一个条件查询的例子是将简单地返回对应于Employee类的每个对象。

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

限制与标准:
可以使用add()方法可用于Criteria对象添加限制条件查询。下面是例子增加一个限制与薪水返回的记录是等于2000:

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

以下是几个例子覆盖不同的场景,并且可以根据要求使用:

 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 可以创建AND或OR使用LogicalExpression限制如下条件:
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();

虽然上述所有条件,可以直接使用HQL在前面的教程中介绍。

分页使用标准:
还有的标准接口,用于分页的两种方法。

  • public Criteria setFirstResult(int firstResult)
  • 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:

1 Criteria cr = session.createCriteria(Employee.class);
2 cr.setFirstResult(1);
3 cr.setMaxResults(10);
4 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:

 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();

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:

 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:
考虑下面的POJO类:

 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 }

让我们创建下面的EMPLOYEE表来存储Employee对象:

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 );

以下将被映射文件

 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:

  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 }

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。

转自http://www.jb51.net/article/76764.htm 

posted @ 2016-11-09 09:39  丶疏影横斜  阅读(4070)  评论(0编辑  收藏  举报