Example On Hibernate Update Query

This is the program to update an object (1 complete row) in the database, which is already persisted in the database, then we have the following two approaches…

Approach 1

Load that object from the database, and modify its values, now hibernate automatically modifies the values on to database also, when ever the transaction is committed.

Approach 2:

If we want to modify object in the database, then create new object with same id and we must call update() given by session interface.
Files required to execute this program..

• Product.java (My POJO class)
• product.hbm.xml (Xml mapping file )
• hibernate.cfg.xml (Xml configuration file)
• ClientProgram.java(java file to write our hibernate logic)

Related to approach 1:

Product.java (POJO)

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package str;   public class Product{       private int productId;     private String proName;     private double price;       public void setProductId(int productId)     {         this.productId = productId;     }     public int getProductId()     {         return productId;     }       public void setProName(String proName)     {         this.proName = proName;     }     public String getProName()     {         return proName;     }       public void setPrice(double price)     {         this.price = price;     }     public double getPrice()     {         return price;     } }

Product.hbm.xml

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xml version="1.0"?> "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">   <hibernate-mapping> <class name="str.Product" table="products">   <id name="productId" column="pid"  /> <property name="proName" column="pname" length="10"/> <property name="price"/>   </class> </hibernate-mapping>

hibernate.cfg.xml

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xml version='1.0' encoding='UTF-8'?> "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">   <hibernate-configuration> <session-factory> <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver </property> <property name="connection.url">jdbc:oracle:thin:@www.java4s.com:1521:XE</property> <property name="connection.username">system</property> <property name="connection.password">admin</property>   <property name="dialect">org.hibernate.dialect.OracleDialect</property> <property name="show_sql">true</property> <property name="hbm2ddl.auto">update</property>   <mapping resource="Product.hbm.xml"></mapping> </session-factory> </hibernate-configuration>

ClientProgram.java (* Recommended way)

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package str;   import org.hibernate.*; import org.hibernate.cfg.*;   public class ForOurLogic {       public static void main(String[] args)     {           Configuration cfg = new Configuration();         cfg.configure("hibernate.cfg.xml");           SessionFactory factory = cfg.buildSessionFactory();         Session session = factory.openSession();         Object o=session.load(Product.class,new Integer(105));         Product s=(Product)o;           Transaction tx = session.beginTransaction();      //s.setStno(105);   should not update, because we loaded with that number right..?         s.setPrice(4000);   // implicitly update method will be called..           tx.commit();           System.out.println("Object Updated successfully.....!!");         session.close();         factory.close();     }   }

Notes:

• See line number 20, actually there i tried to update Stno(105), we should not do this, because we have loaded the object from the database with his id number only, see line number 16, if we update hibernate will rises the exception
• See line number 24 once we call the commit(), automatically update method will be called by hibernate.
• When ever an object is loaded from the database then hibernate stores the loaded object in cache-memory maintained by session-interface
• Once an object is loaded, if we do any modifications on that object by calling its setter methods, then these modification are stored in the object maintained by cache-memory
• if we modify the loaded object for multiple times then also the modifications will be stored in object maintained by the cache-memory only.
• when ever we issue commit() operation then hibernate verify whether any changes are there between the object stored in the cache and object in the database, if changes exists then hibernate automatically updates the database by generating any update operation.
• What am saying is hibernate automatically maintains synchronization between cache-memory object and database table objects (rows)

Related to approach 2:

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package str;   import org.hibernate.*; import org.hibernate.cfg.*;   public class ForOurLogic {       public static void main(String[] args)     {           Configuration cfg = new Configuration();         cfg.configure("hibernate.cfg.xml");           SessionFactory factory = cfg.buildSessionFactory();         Session session = factory.openSession();              Product p=new Product();         p.setProductId(104);  // 104 must be in the DB         p.setProName("Someting");                 Transaction tx = session.beginTransaction();             session.update(p);         tx.commit();           System.out.println("Object Updated successfully.....!!");         session.close();         factory.close();     }   }