Hibernate Tutorial
Hibernate tutorial
1. Introduction
Hibernate; the latest Open Source persistence technology at the heart of J2EE EJB 3.0 is available for download from Hibernet.org.The
- Hibernate 3.0 provides three full-featured query facilities: Hibernate Query Language, the newly enhanced Hibernate Criteria Query API, and enhanced support for queries expressed in the native SQL dialect of the database.
- Filters for working with temporal (historical), regional or permissioned data.
- Enhanced Criteria query API: with full support for projection/aggregation and subselects.
- Runtime performance monitoring: via JMX or local Java API, including a second-level cache browser.
- Eclipse support, including a suite of Eclipse plug-ins for working with Hibernate 3.0, including mapping editor, interactive query prototyping, schema reverse engineering tool.
- Hibernate is Free under LGPL: Hibernate can be used to develop/package and distribute the applications for free.
- Hibernate is Scalable: Hibernate is very performant and due to its dual-layer architecture can be used in the clustered environments.
- Less Development Time: Hibernate reduces the development timings as it supports inheritance, polymorphism, composition and the Java Collection framework.
- Automatic Key Generation: Hibernate supports the automatic generation of primary key for your table
- EJB3-style persistence operations: EJB3 defines the create() and merge() operations, which are slightly different to Hibernate's saveOrUpdate() and saveOrUpdateCopy() operations. Hibernate3 will support all four operations as methods of the Session interface.
- Hibernate XML binding enables data to be represented as XML and POJOs interchangeably.
- The EJB3 draft specification support for POJO persistence and annotations.
Hibernate Architecture
The above diagram shows that Hibernate is using the database and configuration data (properties and xml mapping) to provide persistence services (and persistent objects) to the application.
To use Hibernate, it is required to create Java classes that represents the table in the database and then map the instance variable in the class with the columns in the database. Then Hibernate can be used to perform operations on the database like select, insert, update and delete the records in the table. Hibernate automatically creates the query to perform these operations.
Hibernate architecture has three main components:
- Connection Management: - Hibernate Connection management service provide efficient management of the database connections. Database connection is the most expensive part of interacting with the database as it requires a lot of resources of open and close the database connection.
- Transaction Management: - Transaction management service provides the ability to the user to execute more than one database statements at a time.
- Object relational Mapping: - Object relational mapping is technique of mapping the data representation from an object model to a relational data model. This part of the Hibernate is used to select, insert, update and delete the records form the underlying table. When we pass an object to a Session.save() method, Hibernate reads the state of the variables of that object and executes the necessary query.
- Hibernate is very good tool as far as object relational mapping , but in terms of connection management and transaction management, it is lacking in performance and capabilities. So usually hibernate is being used with other connection management and transaction management tools. For example apache DBCP is used for connection pooling with the Hibernate.
-
Hibernate provides a lot of flexibility in use. It is called "Lite" architecture when we only use the object relational mapping component. While in "Full Cream" architecture all the three component Object Relational mapping, Connection Management and Transaction Management) are used.
Hibernate ExampleThis section demonstrates how to create a simple program to insert record in Oracle database. You can run this program from Eclipse or from command prompt as well.
Configuring Hibernate:-
In this application Hibernate provided the connection pooling and transaction management is used for simplicity. Hibernate uses the hibernate.cfg.xml to create the connection pool and setup required environment. Here is the code:
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
oracle.jdbc.driver.OracleDriver
jdbc:oracle:thin:@192.168.1.176:1521:CAM
In the above configuration file we specified to use the "
Hibernate, supports many database. With the use of the Hibernate (Object/Relational Mapping and Transparent Object Persistence for Java and SQL Databases), we can use the following databases dialect type property:
· DB2 - org.hibernate.dialect.DB2Dialect
· HypersonicSQL - org.hibernate.dialect.HSQLDialect
· Informix - org.hibernate.dialect.InformixDialect
· Ingres - org.hibernate.dialect.IngresDialect
· Interbase - org.hibernate.dialect.InterbaseDialect
· Pointbase - org.hibernate.dialect.PointbaseDialect
· PostgreSQL - org.hibernate.dialect.PostgreSQLDialect
· Mckoi SQL - org.hibernate.dialect.MckoiDialect
· Microsoft SQL Server - org.hibernate.dialect.SQLServerDialect
· MySQL - org.hibernate.dialect.MySQLDialect
· Oracle (any version) - org.hibernate.dialect.OracleDialect
· Oracle 9 - org.hibernate.dialect.Oracle9Dialect
· Progress - org.hibernate.dialect.ProgressDialect
· FrontBase - org.hibernate.dialect.FrontbaseDialect
· SAP DB - org.hibernate.dialect.SAPDBDialect
· Sybase - org.hibernate.dialect.SybaseDialect
· Sybase Anywhere - org.hibernate.dialect.SybaseAnywhereDialect
The
Hibernate JDBC Properties used :-
hibernate.connection.driver_class :-jdbc driver class
hibernate.connection.url :- jdbc URL
hibernate.connection.username :- database user
hibernate.connection.password :- database user password
hibernate.connection.pool_size :- maximum number of pooled connections
Hibernate.dialect :-The classname of a Hibernate Dialect
hibernate.show_sql :-Write all SQL statements to console (True/false).
hibernate.hbm2ddl.auto :- Automatically export schema DDL to the database when the SessionFactory is created. With create drop, the database schema will be dropped when the SessionFactory is closed explicitly. e.g. update | create | create-drop
Writing First Persistence Class: - Hibernate, uses the Plain Old Java Objects (POJOs) classes to map to the database table. We can configure the variables to map to the database column. Here is the code for Book. java:
/**
* Java Class to map to the database Book table
*/
package avakaya.book;
public class Book
{
private String bookId;
private String strBookName;
/**
* @return Returns the strBookName.
*/
public String getStrBookName()
{
return strBookName;
}
/**
* @param strBookName The strBookName to set.
*/
public void setStrBookName(String strBookName)
{
this.strBookName = strBookName;
}
/**
* Method getBookId
* Description :
* @return
*/
public String getBookId()
{
return bookId;
}
/**
* Method setBookId
* Description :
* @param string
*/
public void setBookId(String string)
{
bookId = string;
}
}
Mapping the Contact Object to the Database Contact table :- The file contact.hbm.xml is used to map Contact Object to the Contact table in the database. Here is the code for book.hbm.xml:
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
Setting Up Database :- Create a table Contact under the data base.
CREATE TABLE BOOK ( ID VARCHAR2(10 BYTE), NAME VARCHAR2(10 BYTE) ) LOGGING NOCACHE NOPARALLEL;
Developing Code to Test Hibernate example:-
package avakaya.book;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
/**
* Hibernate example to inset data into Book table
*/
public class BookAccess
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
//Create new instance of Contact and set values in it by reading them from form object
System.out.println("Inserting Record");
Book book = new Book();
book.setBookId("12348");
book.setStrBookName("MyBook2");
session.save(book);
tx.commit();
System.out.println("Done");
}
catch (Exception e)
{
e.printStackTrace();
System.out.println(e.getMessage());
}
finally
{
if (session != null)
{
session.flush();
session.close();
}
}
}
Hibernate O/R mapping -A Look
Let us consider the following file to understand O/R Mapping
Hibernate mapping documents are simple xml documents. Here are important elements of the mapping file:.
The first or root element of hibernate mapping document is
· class element(s) are present.
·
The
·
The
primary key maps to the ID field of the table CONTACT. The attributes of the id element are:
o name: The property name used by the persistent class.
o column: The column used to store the primary key value.
o type: The Java data type used.
o unsaved-value: This is the value used to determine if a class has been made persistent. If the value of the id attribute is null, then it means that this object has not been persisted.
·
The
* Increment - This is used to generate primary keys of type long, short or int that are unique only. It should not be used in the clustered deployment environment.
* Sequence - Hibernate can also use the sequences to generate the primary key. It can be used with DB2, PostgreSQL, Oracle, SAP DB databases.
* Assigned - Assigned method is used when application code generates the primary key.
·
The property elements define standard Java attributes and their mapping into database schema. The property element supports the column child element to specify additional properties, such as the index name on a column or a specific column type.
1.1. Understanding Hibernate element
In this section we will look into the
The
This is the optional element under
Here is the lists of some commonly used generators in hibernate:
| Generator | Description |
| increment | It generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. It should not the used in the clustered environment. |
| identity | It supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. The returned identifier is of type long, short or int. |
| sequence | The sequence generator uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator in Interbase. The returned identifier is of type long, short or int |
| | The |
| seqhilo | The seqhilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a named database sequence. |
| uuid | The uuid generator uses a 128-bit UUID algorithm to generate identifiers of type string, unique within a network (the IP address is used). The UUID is encoded as a string of hexadecimal digits of length 32. |
| guid | It uses a database-generated GUID string on MS SQL Server and MySQL. |
| native | It picks identity, sequence or |
| assigned | lets the application to assign an identifier to the object before save() is called. This is the default strategy if no |
| select | retrieves a primary key assigned by a database trigger by selecting the row by some unique key and retrieving the primary key value. |
| foreign | uses the identifier of another associated object. Usually used in conjunction with a |
1.1. Using Hibernate to generate id incrementally
As we have seen in the last section that the increment class generates identifiers of type long, short or int that is unique only when no other process is inserting data into the same table. In this lesson I will show you how to write running program to demonstrate it. You should not use this method to generate the primary key in case of clustured environment.
In this section we will create/alter table in database, add mappings in the book.hbm.xml file, develop/modify the POJO class (Book.java), and write the program to test it out.
Create Table in the database:
User the following sql statement to create a new table in the database
CREATE TABLE BOOK ( ID INTEGER DEFAULT 0, BOOKNAME VARCHAR2(50 BYTE) DEFAULT NULL ) LOGGING NOCACHE NOPARALLEL;
Developing POJO Class (Book.java)
Book.java is our POJO class which is to be persisted to the database table "book”
/**
* Java Class to map to the database Book table
*/
package avakaya.book;
/**
* Class Book
* Description : POJO
* @version $Revision: 1.0 $
*/
public class Book {
private int lngBookId;
private String strBookName;
/**
* @return Returns the lngBookId.
*/
public int getLngBookId() {
return lngBookId;
}
/**
* @param lngBookId The lngBookId to set.
*/
public void setLngBookId(int lngBookId) {
this.lngBookId = lngBookId;
}
/**
* @return Returns the strBookName.
*/
public String getStrBookName() {
return strBookName;
}
/**
* @param strBookName The strBookName to set.
*/
public void setStrBookName(String strBookName) {
this.strBookName = strBookName;
}
}
Adding Mapping entries to existing.hbm.xml / book.hbm.xml
Add the following mapping code into the contact.hbm.xml file
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
Note:- We have used
Adding
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
oracle.jdbc.driver.OracleDriver
jdbc:oracle:thin:@192.168.1.176:1521:CAM
Write the client program and test it out
Here is the code of our client program to test the application
/****************************************************************************
* @(#) IdIncrementExample.java Feb 22, 2006
****************************************************************************/
package avakaya.book;
//Hibernate Imports
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
/**
* Class
* Description :
* @version $Revision: 1.0 $
* @author Avakaya R
*
*/
public class IdIncrementExample
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
org.hibernate.Transaction tx = session.beginTransaction();
//Create new instance of Contact and set values in it by reading them from form object
System.out.println("Inserting Book object into database..");
Book book = new Book();
book.setStrBookName("Hibernate Tutorial2");
session.save(book);
System.out.println("Book object persisted to the database.");
tx.commit();
session.flush();
session.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
}
}
}
Hibernate Query Language or HQL for short is extremely powerful query language. HQL is much like SQL and are case-insensitive, except for the names of the Java Classes and properties. Hibernate Query Language is used to execute queries against database. Hibernate automatically generates the sql query and execute it against underlying database if HQL is used in the application. HQL is based on the relational object models and makes the SQL object oriented. Hibernate Query Language uses Classes and properties instead of tables and columns. Hibernate Query Language is extremely powerful and it supports Polymorphism, Associations, Much less verbose than SQL.
There are other options that can be used while using Hibernate. These are Query By Criteria (QBC) and Query BY Example (QBE) using Criteria API and the Native SQL queries. In this section we will understand HQL in detail.
Why to use HQL?
- Full support for relational operations: HQL allows representing SQL queries in the form of objects. Hibernate Query Language uses Classes and properties instead of tables and columns.
- Return result as Object: The HQL queries return the query result(s) in the form of object(s), which is easy to use. This elemenates the need of creating the object and populate the data from result set.
- Polymorphic Queries: HQL fully supports polymorphic queries. Polymorphic queries results the query results along with all the child objects if any.
- Easy to Learn: Hibernate Queries are easy to learn and it can be easily implemented in the applications.
- Support for Advance features: HQL contains many advance features such as pagination, fetch join with dynamic profiling, Inner/outer/full joins, Cartesian products. It also supports Projection, Aggregation (max, avg) and grouping, Ordering, Sub queries and SQL function calls.
- Database independent: Queries written in HQL are database independent (If database supports the underlying feature).
Understanding HQL Syntax
Any Hibernate Query Language may consist of following elements:
- Clauses
- Aggregate functions
- Subqueries
Clauses in the HQL are:
- from
- select
- where
- order by
- group by
Aggregate functions are:
- avg(...), sum(...), min(...), max(...)
- count(*)
- count(...), count(distinct ...), count(all...)
Subqueries
Subqueries are nothing but it’s a query within another query. Hibernate supports Subqueries if the underlying database supports it.
1.1. Preparing table for HQL Examples
Create an insurance table
CREATE TABLE Insurance (
ID INTEGER default 0,
insurance_name varchar(50) default NULL,
invested_amount INTEGER default NULL,
investement_date DATE default NULL,
PRIMARY KEY (ID)
1.1. Writing ORM for Insurance table
Create POJO class:
Here is the code of our java file (Insurance.java), which we will map to the insurance table
/****************************************************************************
* @(#) Insurance.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import java.util.Date;
/**
* Class
* Description : POJO Class
* @author Avakaya R
*
*/
public class Insurance
{
private int lngInsuranceId;
private String insuranceName;
private int investementAmount;
private Date investementDate;
/**
* Method getInsuranceName
* Description :
* @return
*/
public String getInsuranceName()
{
return insuranceName;
}
/**
* Method getInvestementAmount
* Description :
* @return
*/
public int getInvestementAmount()
{
return investementAmount;
}
/**
* Method getInvestementDate
* Description :
* @return
*/
public Date getInvestementDate()
{
return investementDate;
}
/**
* Method getLngInsuranceId
* Description :
* @return
*/
public int getLngInsuranceId()
{
return lngInsuranceId;
}
/**
* Method setInsuranceName
* Description :
* @param string
*/
public void setInsuranceName(String string)
{
insuranceName = string;
}
/**
* Method setInvestementAmount
* Description :
* @param i
*/
public void setInvestementAmount(int i)
{
investementAmount = i;
}
/**
* Method setInvestementDate
* Description :
* @param date
*/
public void setInvestementDate(Date date)
{
investementDate = date;
}
/**
* Method setLngInsuranceId
* Description :
* @param i
*/
public void setLngInsuranceId(int i)
{
lngInsuranceId = i;
}
}
Adding mappings into existing.hbm.xml file / insurance.hbm.xml
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
Adding
"-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
oracle.jdbc.driver.OracleDriver
jdbc:oracle:thin:@192.168.1.176:1521:CAM
1.1. HQL from clause Example
In this example you will learn how to use the HQL from clause. The from clause is the simplest possible Hibernate Query.
Syntax :-
From <
Example of from clause is:
from Insurance insurance
Here is the full code of the from clause example:
/****************************************************************************
* @(#) FromClauseHQLExample.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import java.util.Iterator;
import org.hibernate.Session;
import org.hibernate.*;
import org.hibernate.cfg.*;
public class FromClauseHQLExample
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
//Using from Clause
String SQL_QUERY = "from Insurance insurance"; // use from to get all records
Query query = session.createQuery(SQL_QUERY);
for (Iterator it = query.iterate(); it.hasNext();)
{
Insurance insurance = (Insurance)it.next();
System.out.println("ID: " + insurance.getLngInsuranceId());
System.out.println(
"First Name: " + insurance.getInsuranceName());
}
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
session.flush();
session.close();
}
}
}
1.1. Hibernate Select Clause
In this section we will write example code to select the data from Insurance table using Hibernate Select Clause. The select clause picks up objects and properties to return in the query result set.
Syntax
Select <
Here is the query example:
Select insurance.lngInsuranceId, insurance.insuranceName, insurance.investementAmount, insurance.investementDate from Insurance insurance
This selects all the rows (insurance.lngInsuranceId, insurance.insuranceName, insurance.investementAmount, insurance.investementDate) from Insurance table,
Hibernate generates the necessary sql query and selects all the records from Insurance table. Here is the code of our java file which shows how select HQL can be used:
/****************************************************************************
* @(#) SelectClauseExample.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class SelectClauseExample
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
//Create Select Clause HQL
String SQL_QUERY =
"Select insurance.lngInsuranceId,insurance.insuranceName,"
+ "insurance.investementAmount,insurance.investementDate from Insurance insurance";
Query query = session.createQuery(SQL_QUERY);
for (Iterator it = query.iterate(); it.hasNext();)
{
Object[] row = (Object[])it.next();
System.out.println("ID: " + row[0]);
System.out.println("Name: " + row[1]);
System.out.println("Amount: " + row[2]);
}
session.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
}
}
}
1.1. HQL Where Clause Example
Where Clause is used to limit the results returned from database. It can be used with aliases and if the aliases are not present in the Query, the properties can be referred by name. For example:
from Insurance where lngInsuranceId='1'
Where Clause can be used with or without Select Clause. Here the example code:
/****************************************************************************
* @(#) WhereClauseExample.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class WhereClauseExample
{
public static void main(String[] args) {
Session session = null;
try{
// This step will read hibernate.cfg.xml and prepare hibernate for use
SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
session =sessionFactory.openSession();
System.out.println("*******************************");
System.out.println("Query using Hibernate Query Language");
//Query using Hibernate Query Language
String SQL_QUERY =" from Insurance as insurance where insurance.lngInsuranceId='1'";
Query query = session.createQuery(SQL_QUERY);
for(Iterator it=query.iterate();it.hasNext();){
Insurance insurance=(Insurance)it.next();
System.out.println("ID: " + insurance.getLngInsuranceId());
System.out.println("Name: " + insurance.getInsuranceName());
}
System.out.println("*******************************");
System.out.println("Where Clause With Select Clause");
//Where Clause With Select Clause
SQL_QUERY ="Select insurance.lngInsuranceId,insurance.insuranceName," +
"insurance.investementAmount,insurance.investementDate from Insurance insurance "+
" where insurance.lngInsuranceId='1'";
query = session.createQuery(SQL_QUERY);
for(Iterator it=query.iterate();it.hasNext();){
Object[] row = (Object[]) it.next();
System.out.println("ID: " + row[0]);
System.out.println("Name: " + row[1]);
}
System.out.println("*******************************");
session.close();
}catch(Exception e){
System.out.println(e.getMessage());
}finally{
}
}
}
1.2. HQL Group By Clause Example
Group by clause is used to return the aggregate values by grouping on returned component. HQL supports Group By Clause. In our example we will calculate the sum of invested amount in each insurance type. Here is the java code for calculating the invested amount insurance wise
/****************************************************************************
* @(#) HQLGroupByExample.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import java.util.Iterator;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HQLGroupByExample
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for
// use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
//Group By Clause Example
String SQL_QUERY =
"select sum(insurance.investementAmount),insurance.insuranceName "
+ "from Insurance insurance group by insurance.insuranceName";
Query query = session.createQuery(SQL_QUERY);
for (Iterator it = query.iterate(); it.hasNext();)
{
Object[] row = (Object[])it.next();
System.out.println("Invested Amount: " + row[0]);
System.out.println("Insurance Name: " + row[1]);
}
session.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
}
}
}
1.1. HQL Order By Example
Order by clause is used to retrieve the data from database in the sorted order by any property of returned class or components. HQL supports Order By Clause. In our example we will retrieve the data sorted on the insurance type. Here is the java example code:
/****************************************************************************
* @(#) HQLOrderByExample.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import org.hibernate.Session;
import org.hibernate.*;
import org.hibernate.cfg.*;
import java.util.*;
public class HQLOrderByExample
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for
// use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
//Order By Example
String SQL_QUERY =
" from Insurance as insurance order by insurance.insuranceName";
Query query = session.createQuery(SQL_QUERY);
for (Iterator it = query.iterate(); it.hasNext();)
{
Insurance insurance = (Insurance)it.next();
System.out.println("ID: " + insurance.getLngInsuranceId());
System.out.println("Name: " + insurance.getInsuranceName());
}
session.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
}
}
}
1. Hibernate Criteria Query Example
The Criteria interface allows to create and execute object-oriented queries. Criteria Query is used mostly in case of multi criteria search screens, where HQL is not very effective.
The interface org.hibernate.Criteria is used to create the criterion for the search. The org.hibernate.Criteria interface represents a query against a persistent class. The Session is a factory for Criteria instances. Here is a simple example of Hibernate Criterial Query for the insurance table created earlier
/****************************************************************************
* @(#) HibernateCriteriaQueryExample.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import java.util.Iterator;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateCriteriaQueryExample
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for
// use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
//Criteria Query Example
Criteria crit = session.createCriteria(Insurance.class);
java.util.List insurances = crit.list();
for (Iterator it = insurances.iterator(); it.hasNext();)
{
Insurance insurance = (Insurance)it.next();
System.out.println("ID: " + insurance.getLngInsuranceId());
System.out.println("Name: " + insurance.getInsuranceName());
}
session.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
}
}
}
The above Criteria Query example selects all the records from the table and displays on the console. In the above code the following code creates a new Criteria instance, for the class Insurance:
Criteria crit = session.createCriteria(Insurance.class);
The code:
List insurances = crit.list();
creates the sql query and execute against database to retrieve the data.
1.1. Criteria Query Examples
In the last lesson we learnt how to use Criteria Query to select all the records from Insurance table. In this lesson we will learn how to restrict the results returned from the database. Different method provided by Criteria interface can be used with the help of Restrictions to restrict the records fetched from database.
Criteria Interface provides the following methods:
| Method | Description |
| add | The Add method adds a Criterion to constrain the results to be retrieved. |
| addOrder | Add an Order to the result set. |
| createAlias | Join an association, assigning an alias to the joined entity |
| createCriteria | This method is used to create a new Criteria, "rooted" at the associated entity. |
| setFetchSize | This method is used to set a fetch size for the underlying JDBC query. |
| setFirstResult | This method is used to set the first result to be retrieved. |
| setMaxResults | This method is used to set a limit upon the number of objects to be retrieved. |
| uniqueResult | This method is used to instruct the Hibernate to fetch and return the unique records from database. |
Class Restriction provides built-in criterion via static factory methods. Important methods of the Restriction class are:
| Method | Description |
| Restriction.allEq | This is used to apply an "equals" constraint to each property in the key set of a Map |
| Restriction.between | This is used to apply a "between" constraint to the named property |
| Restriction.eq | This is used to apply an "equal" constraint to the named property |
| Restriction.ge | This is used to apply a "greater than or equal" constraint to the named property |
| Restriction.gt | This is used to apply a "greater than" constraint to the named property |
| Restriction.idEq | This is used to apply an "equal" constraint to the identifier property |
| Restriction.ilike | This is case-insensitive "like", similar to Postgres ilike operator |
| Restriction.in | This is used to apply an "in" constraint to the named property |
| Restriction.isNotNull | This is used to apply an "is not null" constraint to the named property |
| Restriction.isNull | This is used to apply an "is null" constraint to the named property |
| Restriction.le | This is used to apply a "less than or equal" constraint to the named property |
| Restriction.like | This is used to apply a "like" constraint to the named property |
| Restriction.lt | This is used to apply a "less than" constraint to the named property |
| Restriction.ltProperty | This is used to apply a "less than" constraint to two properties |
| Restriction.ne | This is used to apply a "not equal" constraint to the named property |
| Restriction.neProperty | This is used to apply a "not equal" constraint to two properties |
| Restriction.not | This returns the negation of an expression |
| Restriction.or | This returns the disjuction of two expressions |
Here is an example code that shows how to use Restrictions.like method and restrict the maximum rows returned by query by setting the Criteria.setMaxResults() value to 5.
/****************************************************************************
* @(#) HibernateCriteriaQueryExample2.java Feb 22, 2006
****************************************************************************/
package avakaya.insurance;
import org.hibernate.Session;
import org.hibernate.*;
import org.hibernate.criterion.*;
import org.hibernate.cfg.*;
import java.util.*;
public class HibernateCriteriaQueryExample2
{
public static void main(String[] args)
{
Session session = null;
try
{
// This step will read hibernate.cfg.xml and prepare hibernate for
// use
SessionFactory sessionFactory =
new Configuration().configure().buildSessionFactory();
session = sessionFactory.openSession();
//Criteria Query Example
Criteria crit = session.createCriteria(Insurance.class);
crit.add(Restrictions.like("insuranceName", "%Life%"));
//Like condition
crit.setMaxResults(5); //Restricts the max rows to 5
List insurances = crit.list();
for (Iterator it = insurances.iterator(); it.hasNext();)
{
Insurance insurance = (Insurance)it.next();
System.out.println("ID: " + insurance.getLngInsuranceId());
System.out.println("Name: " + insurance.getInsuranceName());
}
session.close();
}
catch (Exception e)
{
System.out.println(e.getMessage());
}
finally
{
}
}
}
1 comment:
Awesome information, many thanks to the article writer. It’s understandable to me now, the effectiveness and importance is mind-boggling. Thank you once again and good luck!
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