ORM features in hibernate

Hibernate is Object Relational Mapping(ORM) framework. Hibernate has the advantages while comparing with JDBC. That advantages will make developer life will be easy were implementing or maintaining the java application. Hibernate ORM features are,
  • Hibernate gives the support of POJO/POJI model programming.
  • It is also API independent.
  • Light weight technology, no need of web or application servers.
  • No byte code enhancement like EJB.
  • Supports inheritance and polymorphism features. EJB component do not support inheritance.
  • Pluggable with any Java/JEE or framework software based applications.
  • The persistence logic of hibernate application can be access from all type of java client application.
  • Gives implicit middleware services like jdbc connection pooling, transaction management etc..,
  • Gives support to work with third party jdbc connection pooling.
  • Support to call stored procedures and functions.
  • Supports database independent query language called HQL[Hibernate Query Language].
  • Supports object level relationship.
                  1. One-to-One

                  2. One-to-Many
                  3. Many-to-One
                  4. Many-to-Many
  • Uses hibernate specific data structure "Bag" which is advanced to list.
  • The result generated via select operations is serializable object by default.
  • Provides three full-featured query facilities:
                 1. Hibernate Query Language
                 2. Hibernate Criteria Query API
                 3. Native SQL

Hibernate applications are not distributed. Hence the setup of hibernate must reside with the application/component which needs to interact with database software.

Note: Database server can be anywhere through out the world.Still our hibernate application can access our database server just like a jdbc program. But here entire setup should be there at client side as shown in the above diagram.

It's mandatory to have all resources like POJO classes, mapping files and configuration file along with client program in client side environment.

Below diagram gives you the clear cut picture which explains about clear picture,
  1. Server side environment
  2. Client side environment

Hibernate Configuration file:
  • Its a xml file.
  • Any file name *.xml can become hibernate configuration file.
  • Standard name is "hibernate.cfg.xml"
  • Database Level: It is a database level. It means for every database we can have a separate configuration file. Ex: If we are using only one database in our application then we can have only one hibernate configuration file. If we are using two databases in our application then need to use two hibernate configuration files and so on.
  • DTD[Document Type Definition]: In beginning of this file we need to specify DTD. It is used to validate xml file while parsing the xml file. It's compulsory to specify DTD. Instead of trying this DTD we can copy and paste it from existing predefined examples from 'hibernate-home\etc\hibernate.cfg.xml' file.
  • Then we need to configure all required properties of configuration file. Then we can go for configuring all the mapping files.
  • This file contains hibernate properties having values that are required to establish connection with database software and pass special instruction to database software and hibernate software.
  • Using these details hibernate software constructs a pool of hibernate session objects represented by hibernate session factory object.
  • Each hibernate session object encapsulates the functionality of jdbc connection object and statement object.
Properties of Hibernate Configuration file: In configuration file we need to configure the following 5 properties mandatory.
  • hibernate.dialect
  • hibernate.connection.driver_class(Oracle)/hibernate.connection.driver(MySQL)
  • hibernate.connection.url
  • hibernate.connection.username
  • hibernate.connection.password
Note: These properties need not to follow any order. Driver class, url, username and password are same like jdbc program.

Dialect class:
  • Its a database specific class. It means it differs from one database to another database.
  • Dialect  classes are provided by hibernate api.
  • Using dialect class our hibernate engine can know all the inner details about underlying database server. So that it can generate database specific queries at run time of program.
  • For MySQL database software: org.hibernate.dialect.MySQLDialect
  • for oracle 9i: org.hibernate.dialect.Oracle9Dialect
  • for other versions of oracle: org.hibernate.dialect.OracleDialect
There are many properties in hibernate configuration file. But most of the properties are having regularly used default values.

Hibernate mapping file:
  • Its a xml file.
  • Any file name *.xml can become hibernate mapping file.
  • Naming standard is <Pojo class name>.hbm.xml[hbm indecates hibernate mapping file]
  • DTD[Document Type Definition]: In beginning of this file we need to specify DTD. It is used to validate xml file while parsing the xml file. It is compulsory to specify DTD. DTD file of configuration file and mapping file are different.
  • One hibernate application can have multiple mapping files.
  • All mapping file names must be specified in hibernate.cfg.xml file.
  • We can have a separate mapping file for every pojo class or we can give mappings for multiple pojo classes in a single mapping file.
  • Hibernate mapping file contains OR Mapping configuration like class to table mapping members variables to columns mapping and relationships etc...
Types of Hibernate mappings: Hibernate allows the following OR Mapping file operations in mapping file.
  • Basic OR Mapping:[table-pojo class, table columns – pojo class properties...]
  • Inheritance Mapping:[<subclass>,<joined-subclass>...]
  • Collection Mapping: [<set>,<list>,<map>,<bag>,<idbag>]
  • Association Mapping: [<one-to-one>,<one-to-many>,<many-to-many>...]
  • Component Mapping: [<component> to declare another class object as a property of our pojo class].
Persistent Class [POJO Class]:
  • it is an ordinary java class without having API dependency.
  • An object of this class represents table row.
  • This class and its member variables are mapped with database table and its columns respectively in a hibernate mapping file.
  • Any java class can act as persistent class but it is recommended to take java bean as a persistent class with setter and getter methods.
Key points to remember about Hibernate Application:
  • It can be any Java/JEE application which needs to interact with database server.
  • The code in this application will be written by using hibernate API.
  • We need to follow following steps in our hibernate client application.
  1. Active hibernate engine.
  2. Read configuration file.
  • If hibernate configuration file is named as 'hibernate.cfg.xml' then need not to specify file name.
  • If hibernate configuration file is named other than 'hibernate.cfg.xml' then its compulsory to specify the file name.
  1. Build Session-factory.
  2. Get hibernate session object from session-factory.
  • Create persistent context object.
  • All persistent objects will be stored here.
  1. use session object to perform persistence operations through persistent class objects representing table rows.
  2. Close session object.
  • Release session object back to session-factory.
  • Destroy persistent context object. So that all persistent state objects will be thrown to detached state.
  1. close session-factory. It will destroy the entire session-factory so no more connection pool.
Note:
  • In the above 7 points, first 3 should get executed only once through out the application that too when we start to execute the application.
  • Point 4-6 are part of every client operation. So that every operation can interact with database server.
  • The final step should get executed only once at the time of terminating the application.
Synchronization: The modification what we do to out pojo class/persistent class will be reflected to table row and modification what we do for our table row will be reflected to pojo class object if the object is in persistent state.

How the hibernate program is able to perform synchronization between java object and table rows?
Ans: Every POJO class object that is representing table row will contain primary key value which is one of the number variables of the object. Based up on this primary key value synchronization works.

Hibernate software uses this primary key value as a criteria to update row data using select query and object data with row by using update query.

Note: Programmer configures one or more of the member variables of POJO class as primary key field in hibernate mapping file.

Primary Key: Every record of a table should be identified uniquely. To do this we can configure primary key.

Single field primary key: If only one member variable of POJO class is configured as primary key field then it is called singular field configuration. To configure this we can use <id> tag in mapping file.

Composite primary key: If more than one member variable of POJO class is configured as primary key field then it is called as composite primary key. To configure this we can use <composite-id> tag in mapping file.

If database table primary key is not specified then we can prefer unique key field to configure as a primary key in hibernate mapping file.

Different states of POJO class object: there are 3 states which are as follows,
1. Transient state:
  • Object is created by programmer with data. But is doesn't represent any table row.
  • This object does not contains any primary key value.
  • The object which is created for POJO class and which is not under control of hibernate application resides in transient state.
2. Persistent state:
  • The object that represents table row with primary key and managed under control of hibernate software is called as persistent state.
  • This object will be in synchronization with table row. 
  • Hibernate application developer's uses this kind of object in persistent logic development.
3. Detached state:
  • when session is closed persistent context will be destroyed and all the objects which are in persistent state will be thrown to detached state.
  • when table row of persistent state object is deleted then object becomes detached state.

Location: Bengaluru, Karnataka 560017, India

Comments

Post a Comment

Popular posts from this blog

Hibernate auto increment with example

In previous example we learn how to map java object with database table for manually(not using auto increment) assigned all the values.  To create primary key auto increment application by using hibernate mapping(hbm.xml) or using annotations continue reading this article.  W e need to create a database and create an employee table by using the below query. Table: CREATE table EMPLOYEE( eid integer ( 10 ) primary key not null , firstname varchar ( 30 ), lastname varchar ( 30 ), designation varchar ( 30 ), salary double( 10 , 2 )); Here, we will create a bean/POJO (Plain Old Java Object) class of employee. Employee.java: package com . javatbrains . hibernate ; import java.io.Serializable ; /*This is the POJO class. It contains only Getter and Setter methods*/ public class Employee implements Serializable { private static final long serialVersionUID = - 75885815725314443L ; private int eid ; private String firstName ;
Read more

how to count the page views by using JSP

To count no.of page's are viewed by user in your application is a challenge in real time application. In this page we will see how to count the page views when user has viewed the page.           Here, we will do one example how many times user has visited each page in our application. In this post we will come to know, how to count the total application page views as well as individually each pages count.           Let us assume my web application name is "Page Counter". For creating the web application in eclipse IDE, Click here . This Page Counter contains three pages, assume that are the different pages in an application. But, there is the link between each other files for navigating from one page to another. Also it will show the total pages view count and individual page view count in all the pages. Let us see, below is my first jsp file,           You can declare the below content inside the < body > tag. Rest of the content in every page will b
Read more

Multithreading in java with example

Multithreading  is one of the most important concept in core java. In this article we will learn what is multithreading? , what is the use of it? and What is the use of Synchronization and when to use it?  with detailed examples. At a time, two or more threads are accessing the same object is called as Multithreading  in Java .  First, we will create two threads for two objects. It is also possible to run two or more threads on a single class object. In this case, there is a possibility to get unreliable results. If the two threads are perform same task, then they need same object to be executed each time. For your better understanding, take an example of any reservations like, railway, movie ticket booking,etc. Let us think only one berth is available in a train and two passengers are asking for that berth. The first person has sent a request to allocate that ticket/berth to him. At the same time, the second person also sent a request to allocate that ticket/berth to him
Read more

How to retrieve data from table by using JDBC with example

To retrieve data from mysql data table by using jdbc, we need to confirm weather which table data we need to retrieve. To confirm open your mysql and view all database names by using the ' show databases ' commands in mysql. Then select which is your database name from showing list of database names, by using the ' use <database name> ' command in mysql. Then we need to see all your existing tables by executing the ' show tables ' command. This command gives you the list of existing tables in your selected database. You need to use existing table only you can follow with that. But, here we will see with entirely new which is not existing in mysql database. Now, We will create simple mysql table with minimal columns. create table emp(eno integer(10), ename varchar(30), sal float); The above command creates a new table, we will move further to insert records into emp table by executing the insert which we mentioned in the below.
Read more

Prime, Fibonacci and Factorial number with example in java

Prime number, Fibonacci series and Factorial number programs are most commonly asked questions in interview. Read this article to know what is and how to write programs for prime number, fibonacci series and factorial number. Prime Number: prime number is natural number greater than 1 that has no positive divisor other than 1 and itself. A natural number greater than 1 is not a prime number, is called Composite number . For example, 7 is a prime number. Because it can divide with 1 and 7 only. Where as 8 is composite number. Since it has the divisor 2 and 4 in addition to the 1 and 8. The below example represents the finding the passing number is prime number or not. If the passing number is prime number it will print true otherwise it will print false. package com . javatbrains . practice ; public class PrimeNumber { public boolean isPrimeNumber ( int number ) { if ( number <= 1 ) return false ; // There's only one
Read more

How to insert images into database using JDBC?

How to insert images into database table by using JDBC? To know about these topic follow the below lines,           Before going to write a JDBC program for inserting images into database table, we need to create a specific table for inserting images column datatype. For creating the database table, execute the below command in MySQL command prompt. 1 2 3 4 CREATE TABLE ` images ` ( ` image_id ` int ( 11 ) NOT NULL AUTO_INCREMENT, ` image_flag ` int ( 11 ) NOT NULL , ` image ` longblob NOT NULL , PRIMARY KEY ( ` image_id ` ));           After executing the above query in MySQL command prompt, execute the below query to know weather the above table query is created or not. 1 Show tables;            When you have executed the above query that will show you the list of table which all exists in the current database. Current table is present in that list, then we will move to write the JDBC program to insert images. Otherwise execute the above C
Read more

How to sort list of objects in java with examples

We could achieve list of objects sorting in java by using sort() method which is available under Collections class as well as by using Comparable and Comparator  interfaces. Comparable and Comparator are two interfaces in java used to sort list of objects. These interfaces are available under java.util package along with Collections  class and other classes and interfaces. Comparable interface contains the method of       public int compareTo(Object obj) Comparator interface contains the method of       public int compare(Object obj1, Object obj2) The compare() and compareTo() methods will return negative integer(-1), or zero(0) or positive integer(1). When the first obj1 is less than obj2 method will return negative integer. When obj1 is equals to obj2 will return zero and when obj1 is grater than obj2 it will return positive integer. If it's objects are stored in any Collection classes like ArrayList, HashSet in Array and that time we need to use compare(
Read more

String interview questions and answers

String interview questions and answers are placed the current post as of my experience in interviews. This will helps who are trying to attend interview as fresher as well as experience. If any one is facing any other questions which are not present in the current page, please drop me an email to " subbareddynallamachu@gmail.com ".  Q1:  String is a class or data type? A: String is a class in java.lang package. But, in java, all classes are also are considered as data types. So we can take String as data type also. Q2:  What is the difference between == and equals() methods in java? A: == operator compares the references of the String object. It does not compare the content of the object. equals() method compares the contents. While comparing the Strings, equals method should be used as it yields the correct result. Q3:  What is String constant pool? A: String constant pool is a separate block of memory where the String objects are held by JVM. If a String object is create
Read more

Exception in thread "main" java.lang.NoClassDefFoundError: javax/transaction/SystemException

Exception in thread "main" java.lang.NoClassDefFoundError: javax/transaction/SystemException error we got in Hibernate 4.3 to work with my MySQL database. We are using hibernate code generation tool in Eclipse and we are able to connect to the database using the Hibernate configuration file. When we try to run code in my Main class application is connecting to the database, but transaction is failing and we got the following error: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Exception in thread "main" java . lang . NoClassDefFoundError : javax / transaction / SystemException at java . lang . Class . forName0 ( Native Method ) at java . lang . Class . forName ( Unknown Source ) at org . jboss . logging . Logger . getMessageLogger ( Logger . java : 2248 ) at org . jboss . logging . Logger . getMessageLogger ( Logger . java : 2214 ) at org . hibernate . cfg . Configuration .< clinit >( Configuration . java : 184 ) at be . comp . permanenti
Read more

Store file into table by using JDBC with example

To store large data files or text files into database table, we will use CLOB (Charecter Large Object) datatype of SQL . By using CLOB it is possible to save entire text book or a file or resume into a column of data table. If your using MySQL database instead of CLOB use LONGTEXT to save file into datatable. For saving files into a data table, we need to create one table which will contains a column type as CLOB to store files. Here, is the query to create a data table. 1 2 3 4 create table myfiles( file_id int ( 10 ), file_name varchar ( 30 ), file_type LONGTEXT); Once table creation completes, these table contains the 3 columns one is file_id represents the file id, file_name represents the name of the file and finally file_type will get save entire file into the table column. Now, we will move to write a JDBC program which will saves the file into the newly creating table. Here is the JDBC program, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Read more