Entity framework core - very atypical model relationship

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I have a model (let's call it "foo") that can have multiple children of another model (let's call that one "bar"). Now I would like for foo to have both a collection of child bar models, but I also would like for foo to have a variable of type "bar" that is only populated by the one bar child with "IsActive" set to true. Is this possible with fluent or annotations?

Here is what the classes would sort of look like (not exactly, just enough to get the idea across):

class foo
{
int FooID;
Bar ActiveBar;
ICollection<bar> Bars;
}

class bar
{
int BarID;
int FooID;
bool IsActive;
}

What I have tried:

I looked into the fluent for establishing foreign keys and principal keys, but this is more of a "where" situation.I am now sure where to look for achieving this relationship...if it is even possible.

Posted 3-Aug-21 8:41am

TimWallace

Updated 5-Aug-21 1:45am

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Super Lloyd · Answer 1 · 2021-08-03T17:07:00

Solution 1

how about

C#

class foo
{
  public Bar ActiveBar { get; private set; }
  public IReadonlyCollection<bar> Bars { get; }

  public void SelectBarAt(int index); // <<== magic happens here
}

Posted 3-Aug-21 17:07pm

Super Lloyd

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TimWallace 5-Aug-21 6:26am

Thanks Lloyd, but I was hoping for a way to create a "pure" model - properties only - using Entity Framework Core Code first

Richard Deeming · Answer 2 · 2021-08-05T01:45:00

Assuming you don't actually need that relationship embedded in the database, you can simply do:

C#

class Foo
{
    public ICollection<Bar> Bars { get; set; }
    public Bar ActiveBar => Bars?.FirstOrDefault(b => b.IsActive);
}

You'll probably also want a unique filtered index on the Bar table, so that you can only have one active Bar per Foo:

C#

modelBuilder.Entity<Bar>().HasIndex(b => b.FooID).IsUnique().HasFilter("IsActive = 1");