CODEWITHSUNDEEP
c#asp.net-mvcentity-framework
dav_i
dav_i

Reputation: 28097

When to use DbSet<T>.Add() vs DbSet<T>.Attach()

I have been using Add() and ran into a problem where by a parent entity was being duplicated in the database when Adding a child. Using Attach() solved this but I would like to know why rather than blindly stumbling around.

Upvotes: 38

Views: 22719

Answers (2)

Manzur Alahi
Manzur Alahi

Reputation: 2086

in case of ef-core

Attach is good for cases when you are adding a new entity to the database with navigational properties. Attach only marks newly created items as changed.

Let's say you are adding a new Employee to an Industry. If the industry already exists in the database it must have an ID. and the Employee you are adding is not inserted to the database yet so it does not have an ID yet (I am talking about row IDs here).

So what attach does is since the Industry already has an ID. Attach marks that as Unchanged. And your Employee who doesn't have an ID yet attach marks it as Added.

You can read more about this topic here: https://www.learnentityframeworkcore.com/dbcontext/modifying-data#attach

Upvotes: 7

Anderson Fortaleza
Anderson Fortaleza

Reputation: 2459

Well, when you use Attach you tell the context that the entity is already in the database, SaveChanges will have no effect over attached entities. Add, on the other hand, changes the state of the entity in the context (if it's already there) to Added, meaning it will always insert the entity in the database when you call SaveChanges.

That's the difference.

Upvotes: 39

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