hibernate 標(biāo)準(zhǔn)查詢

hibernate 提供了操縱對(duì)象和相應(yīng)的 rdbms 表中可用的數(shù)據(jù)的替代方法。其中最常用的一種方法是標(biāo)準(zhǔn)的 api，它允許你建立一個(gè)標(biāo)準(zhǔn)的可編程查詢對(duì)象來應(yīng)用過濾規(guī)則和邏輯條件。

hibernate session 接口提供了 createcriteria() 方法，可用于創(chuàng)建一個(gè) criteria 對(duì)象，使當(dāng)您的應(yīng)用程序執(zhí)行一個(gè)標(biāo)準(zhǔn)查詢時(shí)返回一個(gè)持久化對(duì)象的類的實(shí)例。

以下是一個(gè)最簡(jiǎn)單的標(biāo)準(zhǔn)查詢的例子，它只是簡(jiǎn)單地返回對(duì)應(yīng)于員工類的每個(gè)對(duì)象：

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

對(duì)標(biāo)準(zhǔn)的限制

你可以使用 criteria 對(duì)象可用的 add() 方法去添加一個(gè)標(biāo)準(zhǔn)查詢的限制。

以下是一個(gè)示例，它實(shí)現(xiàn)了添加一個(gè)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(gè)例子，涵蓋了不同的情況，可按要求進(jìn)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(dá)式創(chuàng)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(biāo)準(zhǔn)

這里有兩種分頁標(biāo)準(zhǔn)接口方法：

利用上述兩種方法結(jié)合在一起，我們可以在我們的 web 或 swing 應(yīng)用程序構(gòu)建一個(gè)分頁組件。以下是一個(gè)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(jié)果

標(biāo)準(zhǔn) api 提供了 org.hibernate.criterion.order 類可以去根據(jù)你的一個(gè)對(duì)象的屬性把你的排序結(jié)果集按升序或降序排列。這個(gè)例子演示了如何使用 order 類對(duì)結(jié)果集進(jìn)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(yù)測(cè)與聚合

標(biāo)準(zhǔn) 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(gè)獲取預(yù)測(cè)實(shí)例的靜態(tài)工廠方法。

以下是幾個(gè)例子，涵蓋了不同的情況，可按要求進(jìn)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(biāo)準(zhǔn)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(chuàng)建以下員工表來存儲(chǔ) employee 對(duì)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(chuàng)建應(yīng)用程序類來運(yùn)行應(yīng)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(zhí)行

這是編譯并運(yùn)行上述應(yīng)用程序的步驟。確保你有適當(dāng)?shù)?path 和 classpath，然后執(zhí)行編譯程序。

• 按照在配置一章講述的方法創(chuàng)建 hibernate.cfg.xml 配置文件。
• 如上述所示創(chuàng)建 employee.hbm.xml 映射文件。
• 如上述所示創(chuàng)建 employee.java 源文件并編譯。
• 如上述所示創(chuàng)建 manageemployee.java 源文件并編譯。
• 執(zhí)行 manageemployee 二進(jìn)制代碼運(yùn)行程序。

你會(huì)得到下面的結(jié)果，并且記錄將會(huì)在 employee 表創(chuàng)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(yīng)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>