Does Entity Framework Code First support this kind of mapping?

Question

Lets assume I have a class model like so:

public class BlogPost
{
     ...

     [Key]
     public Guid Id {get;private set;}
     public virtual ICollection Comments {get;private set;}
}
public class Comment
{    
     [Key]
     public Guid Id {get;private set;}
     public string Text{get;set;}
}

Don't read too much into my pseudocode here, but what I want to know if: Do the comment class have to have a Guid BlogPostId or BlogPost parent property?

can I model the comment class as I did above, and still have it mapped to the blogpost through the BlogPost.Comments property. e.g. by providing some other mapping attributes

I don't want aggregate members to know anything about their AR.

Sergey Berezovskiy · Accepted Answer · 2013-11-28 13:57:26Z

2

Yes, you are not forced to specify post id (i.e. FK) or reference in comment entity when post have navigation property for comments:

public class BlogPost
{
    public Guid Id { get; private set; }
    public virtual ICollection<Comment> Comments { get; private set; }
}

public class Comment
{
    public Guid Id { get; private set; }
    public string Text { get; set; }
}

In this case EF will generate FK column in Comments table which will have name BlogPost_Id (by default it uses parent entity name with parent entity key property name). Also you don't need to mark key column with [Key] attribute if column has name like id or TypeNameId.

Generated tables will look like:

enter image description here

If you want to change generate FK name without declaring property on comment entity, you can use fluent mappings (generally I suggest you to use fluent mappings instead of data annotation attributes - that will make your entities cleaner). To provide mappings override OnModelCreating method of your data context:

modelBuilder.Entity<BlogPost>()
    .HasMany(bp => bp.Comments)
    .WithRequired()
    .Map(c => c.MapKey("PostId"))
    .WillCascadeOnDelete();

edited Nov 28, 2013 at 13:57

answered Nov 28, 2013 at 13:36

Sergey Berezovskiy

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2 Comments

Roger Johansson Over a year ago

Oohh , nice, didn't think it was smart enough to do this by convention only. thanks :)

Roger Johansson Over a year ago

Is it possible to name the column for the foreign key w/o adding a property for it? e.g. if I want the foreign key to map to an existing column for legacy reasons?

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