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How to create custom ID generator for Entity Framework?

Posted on 2013-05-11
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Last Modified: 2013-05-16
How can I create a custom ID generator for Entity Framework to use a unique string for a primary key?

My client has a requirement that all tables must contain a primary key of a GUID but to be stored as a CHAR(32) without dashes for braces.  Currently, I am having to manually stuff the PK values manually while instantiating entities and/or adding them to collections.  I would really like for Entity Framework to call a small piece of custom logic to create the primary key AND have this generator available in the Designer for model-first design:

id = Guid.NewGuid().Replace("-", "").Replace("{", "").Replace("}", "");

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Question by:MrNMrsGeek
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2 Comments
 
LVL 42

Accepted Solution

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sedgwick earned 1000 total points
ID: 39159198
the following posts explained it:
http://stackoverflow.com/questions/5275306/does-entity-framework-4-code-first-have-support-for-identity-generators-like-nhi
http://stackoverflow.com/questions/5643620/assigning-ids-to-entities-with-entityframework-4

basiaclly, u override OnModelCreating and call HasDatabaseGeneratedOption() with HasDatabaseGeneratedOption.None to disable auto ID generation.
then u override SaveChanges() and use your generation code for the identity column:
public override int SaveChanges()
    {
        foreach (var entry in ChangeTracker.Entries<MyEntity>()
            .Where(e => e.State == EntityState.Added))
        {
            entry.Entity.Id = Guid.NewGuid().Replace("-", "").Replace("{", "").Replace("}", "");
        }

        return base.SaveChanges();
    }
}

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Author Closing Comment

by:MrNMrsGeek
ID: 39172313
Not exactly a generator.  Not exactly what I wanted.  However, this works, I guess.  I was specifically looking for a generator.  Overriding SaveChanges is a hack in that I must either (a) force all of my types to have the same property, or (b) check the entity type within SaveChanges to find all custom types that have said property, or (c) use Reflection to determine IF the object has the property.  None of these are what I want.  My only reason for awarding this as a solution was because it is not sedgwick's fault.
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