javahibernatejpaormlazy-loading

Clarifying terminology - What does "hydrating" a JPA or Hibernate entity mean when fetching the entity from the DB

In the context of ORM / Lazy loading of entities, my understanding of the term "Hydration" is as follows:

"Hydrating" describes the process of populating some or all of the previously unpopulated attributes of an entity fetched using lazy loading.

Eg: class Author is loaded from the database:

@Entity
class Author
{
     @Id
     long id;
     List<Book> books;
}

Initially, the books collection is not populated.

It is my understanding that the process of loading the books collection from the database is referred to as "Hydrating" the collection.

Is this definition correct, and is the term common place? Is there another more common term I should be using for this process?

Solution

  • Hydrate began as a term for populating an instantiated (but empty) value-object/model from a db, (specifically in Hibernate.)

    Various other ORMs and tools like BizTalk use Hydrate and other related terminology, (e.g. BizTalk uses the term Dehydrated to mean an instance is available but not yet populated.)

    Personally I'm averse to redundant terminology overhauls, populated means the same thing, without re-inventing language. It adds nothing and leads to confusion (common first thought on encountering re-invented terms: is this somehow different and magical?).

    The BizTalk extension of this style of language, specifically Dehydrated is redundant. I expect people haven't forgotten how to say, empty, or clear?

    Hydrated and its related metaphors are essentially marketing tools, invented to differentiate Hibernate from competing products.

    At this point Hibernate and other ORM products have used these terms for many years, so Hydrate (and Dehydrate) are here to stay.