CODEWITHSUNDEEP
javahibernatejpa
heez
heez

Reputation: 2659

JPA - What exactly does it mean for an entity object to persist? What is the definition of persistence?

I'm fairly new to java web applications and I am undertaking the task of learning JPA. However, it is not explicitly clear what it means for an entity object to persist. I think I have an idea, but I would rather not assume its meaning.

I am referencing the Oracle JPA Doc, but they continue to use the words like "persist" or "persistence" when describing persistent fields/properties. Can someone shed some light on this idea of persistence? And maybe define what it means for an instance of an entity to be persistent?

And if you could not use the word "persistent" (or any form of the word) in your definition that would be much appreciated. A simple answer would be great, but more in-depth explanations are definitely welcome! Thanks so much!

Upvotes: 12

Views: 9903

Answers (2)

Shabbir Essaji
Shabbir Essaji

Reputation: 619

  • Persistence simply means to Store Permanently.

    • In JAVA we work with Objects and try to store Object's values into database(RDBMS mostly).
    • JPA provides implementation for Object Relation Mapping(ORM) ,so that we can directly store Object into Database as a new Tuple.
    • Object, in JPA, are converted to Entity for mapping it to the Table in Database.

  • So Persisting an Entity means Permanently Storing Object(Entity) into Database.

Hope this Helps!!

Upvotes: 27

duffymo
duffymo

Reputation: 308763

"Persist" means "lives on after the application is shut down". The object is not just in volatile memory; it's in more permanent storage on disk. If the application is shut down, or the user ends their session and begins a new one, the old data is still available from permanent storage on disk.

Databases store information on disks, unless they are in-memory versions that give you the advantage of using SQL but little else. If you use a relational SQL database, you get a query language that makes it easy to Create/Read/Update/Delete information without having to worry about how it's stored on the disk.

SQL databases store relations on disk using different data structures (e.g. B-Tree). Relations are defined in terms of tables and columns. Each record in a table consists of a tuple of row values. Objects have to map tables and columns to objects and attributes using object-relational mapping. JPA generalizes this idea and builds it into Java EE, following the example of implementations like TopLink and Hibernate.

NoSQL databases, like MongoDB, also store information on disk as documents rather than relations.

Object databases serialize an object and all its children using formats like Java serialization, XML, JSON, or custom formats (e.g. Google protocol buffers).

Graph databases, like Neo4J, can be thought of as more general cases of object databases.

Upvotes: 14

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