Introduction to Spring Boot JPA
In this article, I am going to discuss the Introduction to Spring Boot JPA. Please read our previous article where we discussed Spring Boot AOP Other Implementations with Examples.
What is JPA?
JPA or Java Persistence API, is a specification for managing relational data in Java applications. It enables the storage and retrieval of data between Java objects/classes and a relational database using Object-Relation Mapping (ORM).
JPA provides a runtime EntityManager API for processing queries on the database. This API allows us to perform CRUD (Create, Read, Update, Delete) operations on the database. JPA uses a platform-independent object-oriented query language called JPQL (Java Persistent Query Language) to perform these operations.
It is important to note that JPA is not a framework. Instead, it defines a concept that can be implemented by any framework. In the context of persistence, JPA covers three areas: the Java Persistence API itself, Object-Relational metadata, and the API defined in the persistence package.
Spring Boot JPA is an implementation of the JPA specification that integrates with the Spring Boot framework. It provides additional features and simplifies the configuration process for using JPA in Spring Boot applications.
Why should we use JPA?
JPA is easier to use in comparison with other alternatives, such as JDBC (Java Database Connectivity) and SQL (Structured Query Language). JDBC and SQL store data in the form of records and tables, whereas JPA stores data in objects and classes. This makes it easier to work with data in a more object-oriented manner.
JPA is best suited for applications that do not require high performance. It provides several advantages over traditional data access methods. For example, rather than using Data Definition Languages (DDL), such as SQL, to perform queries, JPA uses XML and Java annotations. This makes it easier to define and manage the database schema.
JPA also allows you to save and load Java objects without using any Data Manipulation Languages (DML) at all. This means that we can work with data in a more natural and intuitive way, without having to write complex SQL statements.
JPQL (Java Persistent Query Language) is another advantage of JPA. It allows us to express queries in terms of Java entities rather than native SQL tables and columns. This makes it easier to write and understand queries, as they are closer to the way we think about data in our application.
Overall, JPA provides a more convenient and intuitive way to work with relational data in Java applications.
JPA has several important features that make it a powerful tool for managing relational data in Java applications.
- Repository and custom object-mapping abstraction: This allows easy mapping of Java objects to database tables and vice versa.
- Support for cross-store persistence: This means that we can store an entity partially in different database management systems. For example, we could store part of an entity in a MySQL database and another part in a Neo4j graph database.
- Ability to dynamically generate queries from the names of query methods: This makes it easy to write queries without having to write complex SQL statements. We simply define a method with a name that describes the query we want to perform and JPA will automatically generate the appropriate query.
- Domain base classes provide basic properties that are common to all entities: This makes it easy to define common properties for all entities without having to repeat the same code in each entity class.
- Transparent auditing: This means that we can easily track changes to data and see who made those changes and when.
- Ability to integrate custom repository code with JPA: This allows us to add custom functionality to our repositories and tailor them to our specific needs.
- Ease of integration with Spring Framework using a custom namespace: This makes it easy to use JPA in Spring applications and takes advantage of all its powerful features.
The JPA architecture consists of several units that work together to manage relational data in Java applications.
The Persistence class contains static methods for obtaining an EntityManagerFactory instance. The EntityManagerFactory is a factory class that creates and manages multiple instances of the EntityManager. It is responsible for creating and managing the lifecycle of EntityManager instances.
The EntityManager is an interface that controls persistence operations on objects. It provides methods for persisting, merging, removing, and finding entities. It also works with the Query instance to perform queries on the database.
Entities are persistence objects stored as records in the database. They represent the data that we want to store and retrieve from the database. Entities are defined using annotations or XML mappings.
The Persistence Unit defines a set of all entity classes managed by EntityManager instances in an application. It represents the data contained within a single data store. The Persistence Unit is defined in the persistence.xml file and can include information such as the data source, transaction type, and mapping files.
The EntityTransaction class maintains operations for each EntityManager and has a one-to-one relationship with it. It is responsible for managing transactions when performing persistence operations on entities.
The Query interface is implemented by each JPA vendor to obtain relation objects that meet specific criteria. It provides methods for creating and executing queries on the database.
Overall, the JPA architecture provides a powerful and flexible framework for managing relational data in Java applications.
The JPA architecture can be described using the following diagram:
JPA Class Relationship
All the forementioned classes share a relationship. It can be described using the following diagram:
The diagram can be interpreted as follows:
- The relationship between EntityManager and EntiyTransaction is one-to-one. There is an EntityTransaction instance for each EntityManager operation.
- The relationship between EntityManageFactory and EntiyManager is one-to-many. It is a factory class to EntityManager instance.
- The relationship between EntityManager and Query is one-to-many. We can execute any number of queries by using an instance of EntityManager class.
- The relationship between EntityManager and Entity is one-to-many. An EntityManager instance can manage multiple Entities.
Implementations of JPA
JPA is an open-source specification for managing relational data in Java applications. Various enterprise vendors have implemented JPA in their products. Some of these vendors include Eclipse and Red Hat.
There are several popular implementations of JPA available. Two of the most widely used implementations are Hibernate and EclipseLink. Both of these implementations provide powerful and flexible frameworks for managing relational data in Java applications.
Object-Relation Mapping (ORM) is a technique for mapping Java objects to database tables. It provides a bridge between a relational database, with its tables and records, and a Java application, with its classes and objects.
The ORM layer exists between the application and the database. It is responsible for converting Java classes and objects into a format that can be stored and managed in a relational database. This conversion process is known as mapping. This can be described using the following diagram:
By default, the name of the persisted object becomes the name of the table in the database and its fields become columns. For example, if you have a Java class called “Person” with fields “firstName” and “lastName”, the ORM layer would create a table called “Person” with columns “firstName” and “lastName”.
ORM makes it easier to work with relational data in a more object-oriented manner. Instead of writing complex SQL statements to interact with the database, you can work with your data using Java objects and classes. This makes it easier to develop and maintain your application.
Overall, ORM provides a powerful and flexible way to manage relational data in Java applications.
JPA vs Hibernate
JPA and Hibernate are both used to access, manage, and persist data between Java objects and a relational database. JPA is a Java specification that provides a standard approach for Object-Relation Mapping (ORM), while Hibernate is a lightweight, open-source ORM tool.
One key difference between JPA and Hibernate is that JPA is a specification that only provides interfaces, while Hibernate provides implementation classes. This means that JPA defines the standard for how data should be mapped and persisted, but it does not provide any concrete implementation. Hibernate, on the other hand, provides a concrete implementation of the JPA specification.
Another difference between JPA and Hibernate is the query language they use. JPA uses a platform-independent query language called Java Persistence Query Language (JPQL), while Hibernate uses its own query language called Hibernate Query Language (HQL).
JPA is defined in the javax.persistence package and is implemented by various ORM tools, including Hibernate. It uses EntityManager for handling data persistence. Hibernate, on the other hand, is defined in the org.hibernate package and is a provider of JPA. It uses Sessions for handling data persistence.
Overall, JPA and Hibernate are both powerful tools for managing relational data in Java applications. They have some differences in terms of their implementation and features, but they both provide a convenient and flexible way to work with relational data.
In the next article, I am going to discuss Spring Boot JPA with Examples. Here, in this article, I try to explain the Introduction to Spring Boot JPA. I hope you enjoy this Introduction to Spring Boot JPA article.