Hibernate查詢條件
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();
限製與標準：
可以使用add（）方法可用於Criteria對象添加限製條件查詢。下麵是例子增加一個限製與薪水返回的記錄是等於2000：
Criteria cr = session.createCriteria(Employee.class); cr.add(Restrictions.eq("salary", 2000)); 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：
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"));
可以創建AND或OR使用LogicalExpression限製如下條件：
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();
雖然上述所有條件，可以直接使用HQL在前麵的教學中介紹。
分頁使用標準：
還有的標準接口，用於分頁的兩種方法。
| S.N. | 方法 & 描述 |
|---|---|
| 1 |
public Criteria setFirstResult(int firstResult) This method takes an integer that represents the first row in your result set, starting with row 0. |
| 2 |
public Criteria setMaxResults(int maxResults) This method tells Hibernate to retrieve a fixed number maxResults of objects. |
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。下麵是例子，可以擴展來每次獲取10行：
Criteria cr = session.createCriteria(Employee.class); cr.setFirstResult(1); cr.setMaxResults(10); List results = cr.list();
排序的結果：
標準的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：
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：
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類是類似於類限製，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：
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"));
Criteria Queries 例子：
考慮下麵的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; } }
讓我們創建下麵的EMPLOYEE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) );
以下將被映射文件。
<?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>
最後，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：
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：
下麵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。
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創建hibernate.cfg.xml配置文件中配置章節解釋。
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創建Employee.hbm.xml映射文件，如上圖所示。
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創建Employee.java源文件，如上圖所示，並編譯它。
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創建ManageEmployee.java源文件，如上圖所示，並編譯它。
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執行ManageEmployee二進製運行程序.
會得到以下結果，並記錄將創建在EMPLOYEE表中。
$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
如果檢查EMPLOYEE表，它應該記錄如下：
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>
