Verify if object is already inside Entity Framework context

Question

I'm getting an issue while using EF4, when I'm trying to verify if object is already inside Entity Framework context.

I have this code below

        var entityName = Entity4Test + Guid.NewGuid();

        using( var ctx = new EnviroDataContext() )
        {
            var etc = new Entity
            {
                Name = entityName
            };

            ctx.Entity.AddObject( etc );

                var q = from p in ctx.Entity
                        where p.Name == entityName
                        select p;

// Why 'q.ToList().Count == 0'?

                ctx.SaveChanges();
            }

My question is, why my search after insertion, came out empty?

I know that the data is persisted after 'SaveChanges', but what if I need to 'query' my entity memory data.

Extending the question

I have a business rule that by adding 1 item A, triggers the insertion of others entities B. The issue is, I have validation rule that on insertion of B,t A must already exists.

Because all of these actions are made before 'SaveChanges', I get an error that EntityA doesn't exists.

Other case, I have a Name field that is unique on a table. If I try to run AddEntityName("bla") twice and then 'SaveChanges', I get an exception from DB [Unique constraints], even after passing my validation for insertion, that guaranties that a name is unique.

Anyone have any idea?

RPM1984 · Accepted Answer · 2010-12-09 22:52:13Z

9

When you do .AddObject, it adds it to EF's internal "graph" (memory) in a pending state of "Added".

Only once you do ctx.SaveChanges() will the changes be persisted to the underlying store.

The query you are writing is against the database, and the change hasn't been persisted yet.

So if you execute your query after you do ctx.SaveChanges(), the count will be as expected.

On a side note, if you want to see if an entity is already in the graph (e.g before you "Attach"), read up on ObjectStateManager.TryGetObjectStateEntry.

edited Dec 9, 2010 at 22:52

answered Dec 9, 2010 at 22:46

RPM1984

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4 Comments

muek Over a year ago

I understand what you are saying, but the question is, if that behavior make sense, if you have business rules that implies more insertions and validations?

RPM1984 Over a year ago

@muek - sorry, don't understand your question. What do you mean?

RPM1984 Over a year ago

Right, so your trying to query the 'memory' data - e.g the graph. Well, you cant :) As i said, you can use TryGetObjectStateEntry to see what entities are in the graph, but this is generally used when trying to Attach entities, so you don't get "object key already exists" error. Im still not understanding what your specifically trying to achieve. What exactly are you trying to do in this particular method?

muek Over a year ago

You didn't gave me the answer that I want, but I think that you gave me the one possible. Thanks

Michael Gattuso · Accepted Answer · 2010-12-09 22:18:04Z

1

I haven't used EF4 but have used the previous version so I don't know if their is a different expectation in EF4. It looks like you are attempting to search for the asset in the DB before actually committing it. You should call SaveChanges first then search for it.

answered Dec 9, 2010 at 22:18

Michael Gattuso

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