hibernate 標準查詢

hibernate 提供了操縱對象和相應的 rdbms 表中可用的數據的替代方法。其中最常用的一種方法是標準的 api，它允許你建立一個標準的可編程查詢對象來應用過濾規則和邏輯條件。

hibernate session 接口提供了 createcriteria() 方法，可用于創建一個 criteria 對象，使當您的應用程序執行一個標準查詢時返回一個持久化對象的類的實例。

以下是一個最簡單的標準查詢的例子，它只是簡單地返回對應于員工類的每個對象：

criteria cr = session.createcriteria(employee.class);  
list results = cr.list();

對標準的限制

你可以使用 criteria 對象可用的 add() 方法去添加一個標準查詢的限制。

以下是一個示例，它實現了添加一個限制，令返回工資等于 2000 的記錄：

criteria cr = session.createcriteria(employee.class);    
cr.add(restrictions.eq("salary", 2000));    
list results = cr.list();

以下是幾個例子，涵蓋了不同的情況，可按要求進行使用：

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"));

你可以模仿以下示例，使用邏輯表達式創建 and 或 or 的條件組合：

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();

另外，上述所有的條件都可按之前的教程中解釋的那樣與 hql 直接使用。

分頁使用標準

這里有兩種分頁標準接口方法：

利用上述兩種方法結合在一起，我們可以在我們的 web 或 swing 應用程序構建一個分頁組件。以下是一個例子，利用它你可以一次取出 10 行：

criteria cr = session.createcriteria(employee.class);
cr.setfirstresult(1);
cr.setmaxresults(10);
list results = cr.list();

排序結果

標準 api 提供了 org.hibernate.criterion.order 類可以去根據你的一個對象的屬性把你的排序結果集按升序或降序排列。這個例子演示了如何使用 order 類對結果集進行排序：

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();

預測與聚合

標準 api 提供了 org.hibernate.criterion.projections 類可得到各屬性值的平均值，最大值或最小值。projections 類與 restrictions 類相似，均提供了幾個獲取預測實例的靜態工廠方法。

以下是幾個例子，涵蓋了不同的情況，可按要求進行使用：

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"));

標準查詢示例

考慮下面的 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;
   }
}

讓我們創建以下員工表來存儲 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)
);

以下是映射文件：

<?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，我們將用 main() 方法創建應用程序類來運行應用程序，我們將使用 criteria 查詢：

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();
      }
   }
}

編譯和執行

這是編譯并運行上述應用程序的步驟。確保你有適當的 path 和 classpath，然后執行編譯程序。

• 按照在配置一章講述的方法創建 hibernate.cfg.xml 配置文件。
• 如上述所示創建 employee.hbm.xml 映射文件。
• 如上述所示創建 employee.java 源文件并編譯。
• 如上述所示創建 manageemployee.java 源文件并編譯。
• 執行 manageemployee 二進制代碼運行程序。

你會得到下面的結果，并且記錄將會在 employee 表創建。

$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

如果你檢查你的 employee 表，它應該有以下記錄：

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)
mysql>