Hibernate interfaces explained

In this blog post, I will be explaining some of the interfaces that are commonly used in a Hibernate application

Sample Code

Consider the following code that queries a table via Hibernate:

public class Main {	public static void main(String[] args) {				Person person = new Person("Mickey Mouse",35); //This corresponds to a table called Person with name and age fields		SessionFactory  sessionFactory = new Configuration().configure().buildSessionFactory();		Session session = sessionFactory.openSession();		Transaction tx = session.beginTransaction();		session.save(person);		tx.commit();		session.close();		sessionFactory.close();					}}

Configuration

The Configuration object is the first Hibernate object that you will need to create in any Hibernate application. It encapsulates the Hibernate configuration file i.e. hibernate.cfg.xml. A typical Hibernate application usually creates a Configuration object only once during application initialization. The  configuration.configure method reads the hibernate.cfg.xml file and sets up the Configuration object using the properties in this file. The Configuration object is required to create the SessionFactory object.

SessionFactory

The SessionFactory contains all the data in the hibernate configuration file. The code creates a SessionFactory using a Configuration object. The configuration.buildSessionFactory method sets up the SessionFactory object with the configuration data in the config file. A typical Hibernate application create the SessionFactory object only once at the start of the application and keeps it for later use. The SessionFactory corresponds to the database config file, so if your application connects to several databases with different config files, you will need to have separate SessionFactory objects corresponding to each database.

Session

Next, the code creates a session object. The code uses the sessionFactory.openSession method to create a Session object.  The session represents the physical connection with the database, so whenever a session is created, internally a connection is established to the database. The code uses the session object to actually save data and retrieve data from the database.

Transaction

Next, the code creates a transaction. As you might be aware, in database terminology, a transaction represents a unit of work. So if you want to execute several database operations as a single unit, you can club them into a transaction. A transaction ensures that either all the operations will be executed. If one operation fails the entire transaction will fail. So the database will be reverted to the state that it was before the transaction began. Hibernate defines the transaction interface to represent a transaction.  A transaction is associated with a Session and is usually instantiated by a call to session.beginTransaction(). This gives an instance of the Transaction object. The code can then use the transaction object for committing the changes to the database.

Comments

Post a Comment

Popular posts from this blog

How to use logging in SpringBoot with code samples

Image
In this article, we will learn how to use logging in SpringBoot. Introduction There are several Java logging frameworks like logback, log4j, and so on. Spring Boot supports out-of-the-box support for logback. Let us learn how to use logging in SpringBoot with logback. Step 1 – Create a New Maven Project Create a new Maven project. (Refer to  this  blog post). This will create a project in Eclipse as follows:   Step 2 – Add the Spring Boot Dependencies Add the spring-boot-starter-web dependency to the pom.xml . So, the pom.xml should look as follows: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.learnjava</groupId> <artifactId>learnjava-springboot-logging-example</artifactId> <version>0.0.1-SNAPSHOT&
Read more

Python While Loop with code samples

Much like a Java while loop, you can use a Python while loop to repeatedly execute a block of code as long as a condition is true. In this article, we will learn more about the Python while loop. Python While loop Syntax A while loop in Python has the following syntax: while <condition>: loop body The while keyword is followed by a condition. If the condition evaluates to true, the body of the loop is executed. Once the body of the loop is completed, the condition is checked again and this is repeated until the condition evaluates to false at which point the loop is exited. While loop Sample Code The following code demonstrates how you can use the while loop: num=10counter=1total=0while counter<=num: total += counter counter+=1print("sum of first 10 numbers is",total) This code adds the numbers from 1 to 10 and prints the sum. It uses a while loop to iterate from 1 to 10. The while loop checks the condition counter <= num and if so adds the current value of count
Read more

How to convert a List to a Set

In this blog post ,I will be showing you how you can convert a List to a Set. Consider the following code snippet: public class ListToSetDemo {public static void main(String[] args) {List<Integer> list = Arrays.asList(5,3,11,15,9);//Method 1Set<Integer> set = new HashSet<Integer>(list);System.out.println("Set is "+set);//method 2Set<Integer> set2 = new HashSet<Integer>();set2.addAll(list);System.out.println("Set is "+set2);}} This code demonstrates two ways to convert a List to a Set. Method 1 Here, we are creating a new HashSet . We are invoking the constructor that accepts a Collection object. Here, we are passing in the input list to this constructor.   Method 2 Here again, we are creating a new HashSet . However, we are using the default constructor. We are then invoking the addAll method and passing in the input list.   When you run this code, it will print the following output: Set is [3, 5, 9, 11, 15]Set is [3, 5, 9, 11, 15] No
Read more