Hibernate Tutorial for Beginners

Open-source Hibernate is a free OOP Java framework used in web applications for mapping object-oriented domain models with relational databases.

One may use HQL and SQL to query databases and enable robust object-relational mapping. However, ORM mapping implementation in Java simplifies with Hibernate, reducing significant complexities in your application, and is beneficial for people possessing a fundamental understanding of SQL. 

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Architecture of Hibernate 

Hibernate configuration is typically stored in the properties section or the hibernate.cfg.xml files. When searching for Java configuration, look for classes marked with the annotation @Configuration. 

To start working with a Java application and a database, begin with the Session Factory. The object represents the entire mappings collection between an application’s Java Types and an SQL database.

Session Factory 

Any user application may request a session object by contacting Session Factory. The Session Factory uses the configuration information included in the files to create the session object. Application and database interactions at different moments are included in a session, and a session class represents this. 

Query

Application programs may query the database for one or more stored items using the query language. Hibernate offers a variety of approaches, including NamedQuery and Criteria API, to query the databases. 

First-level Cache 

The cache utilised by the Hibernate Session object communicating with the database on the first level is called the First-level cache, also known as the session cache. It is responsible for caching items in the current session. Every request from the Session object to the database must travel via the first-level cache or the session cache before reaching the database. Therefore, it is essential to notice that the first-level cache remains accessible with the session object until it is no longer active. 

Transactions 

Transactions allow establishing data consistency with the ability to roll back if anything goes wrong. 

Persistent Objects 

Persistent objects are traditional Java objects (POJOs) saved in the database as rows in the linked table by the Hibernate framework. Hibernate configuration files either configure these objects or mark them with the @Entity annotation. 

Second-level Cache 

The second-level cache keeps track of things over several sessions. Enable and provide the cache provider to use second-level cache. For example, EhCache is a popular second-level cache provider in many applications. 

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Key Characteristics of the Hibernate Framework 

Hibernate is a Java domain object mapping framework designed to manage database tables. The framework simplifies working on database items using Java objects rather than SQL statements. In addition, taking care of transaction management, automated primary key creation, managing database connections, and associated implementations contribute to the development process. 

The Java Persistence API (JPA) standard is supported by the JPA provider Hibernate. It is a collection of standards for accessing, storing, and managing data. One can further use the advantage of Java objects and connect it with the relational database entities to ensure complete JPA support. 

High-performance and scalability

While Hibernate can grow in any environment, it offers a wide range of performance-enhancing features such as optimistic locking, lazy initialisation, and several other techniques. 

Simple to keep up with 

Since Hibernate does not need custom database structures or attributes, it can get challenging to manage. It creates SQL during system startup. However, when compared to JDBC, it is easier to maintain.

Classes such as AnnotationConfiguration, ServiceRegistryBuilder, and others have been deprecated rapidly in previous Hibernate versions.

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The Concepts of Entities, Equality, and Identity

Hibernate offers additional concepts to compare objects or characteristics to satisfy precise business rules. Besides preexisting knowledge of checking equalities in Java core, Hibernate concepts are equally important to map.  

1. Association Mappings between Hibernate Entities

When two entities are connected and referred to in a unidirectional or bi-directional way, use JPA annotations to annotate the java classes and turn them into permanent entities. First, however, it is crucial to grasp a few fundamental concepts before generating references between Hibernate entities. 

2. Entity/Persistence are two different things

A Hibernate-mapped object instance carries one of four states: transitory, permanent, detached, or deleted, depending on the object instance state in question. 

3. Cascade Types in Hibernate and JPA 

The “CascadeType” property is used in entities to enable cascade and inverse effects. There are several types of cascading choices accessible via CascadeType. 

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Advantages of Hibernate Annotations vs Mappings 

Before inline annotations, the sole method of creating Hibernate mappings was XML files. Even though different tools from Hibernate and third-party projects enabled automatic production of mappings from the Java source, this was not the case.

Annotations are the most current defined mappings but not the most effective ones. 

Here are a few advantages of Hibernate (or, more accurately, JPA) annotations.

Hibernate Query Language [HQL] is a query language for Hibernate

HQL shares similarities with object-oriented query language SQL. Its operation on permanent objects rather than tables and columns exhibits the functionality of a powerful query language.

JPQL, or Java Persistence Query Language, is a superset. Therefore, a valid JPQL query is considered a good HQL query. However, not all valid HQL queries are valid JPQL queries and vice versa.

Queries for Hibernate Criteria

Using the Criteria Query API, it is possible to construct nested, structured query expressions in Java, allowing for compile-time syntax verification not achievable with a query language like HQL or SQL. In addition to query by example (QBE) functionality, the Criteria API contains other features. 

For example, providing object instances possessing the desired characteristics rather than explaining components of your search step by step may save time and effort. It also contains techniques for projection and aggregation, such as the count method ().

Configuration of the Hibernate EhCache

Caching feature given by ORM frameworks allows users to have a fast-running web application while allowing the framework to decrease queries made in the database for a single transaction. Caching is helpful for users and the framework. Hibernate extends caching at both the first and second levels of the hierarchy.

Conclusion

The Hibernate software is considered a highly functional framework for all things Java. In this Hibernate tutorial, we covered the basics of using Hibernate.

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