EntityManager vs SessionFactory

EntityManager vs SessionFactory: A Comparison

Both EntityManager and SessionFactory are used in Java-based applications for database interactions, but they come from different specifications and have different use-cases and features.

Origin:

• EntityManager: Part of the Java Persistence API (JPA), which is a specification for object-relational mapping in Java.
• SessionFactory: Part of Hibernate, which is an object-relational mapping (ORM) framework. Hibernate can be used as a JPA implementation, but it also has its own native API.

Usage:

• EntityManager: Used to create and remove persistent entity instances, to find entities by their primary key, and to query over entities.
• SessionFactory: Used to create Session instances. A Session represents a single-threaded unit of work. The SessionFactory is a thread-safe global object that is instantiated once.

Configuration:

• EntityManager: Configured via persistence.xml in JPA.
• SessionFactory: Configured via hibernate.cfg.xml or programmatically in Hibernate.

API:

• EntityManager: Provides a higher-level, object-oriented API that includes features like entity state management, automatic dirty checking, and more.
• SessionFactory: Provides a lower-level API that gives you more control over the database interactions but requires you to manage the session and transaction yourself.

Portability:

• EntityManager: Being a JPA specification, the code is generally portable across different JPA providers like Hibernate, EclipseLink, etc.
• SessionFactory: Tightly coupled with Hibernate, making it less portable.

Transactions:

• EntityManager: Transactions are managed by the EntityTransaction API.
• SessionFactory: Transactions are managed by the Transaction API from the Session object.

Query Language:

• EntityManager: Uses JPQL (Java Persistence Query Language) for querying.
• SessionFactory: Uses HQL (Hibernate Query Language), although it can also use native SQL queries.

Features:

• EntityManager: Generally easier to use and set up. Provides sufficient features for most use-cases.
• SessionFactory: Provides more advanced features like caching, lazy loading, and batch processing, which are configurable down to the session level.

Conclusion:

Use EntityManager for most general purposes and when you want to stick to the JPA specification for portability.

Use SessionFactory when you need more control over the session and transactions, or when you need to use Hibernate-specific features.