Get from IQueryable to IEnumerable

Question

this should be a quick one for all you f# rockers, but it's got me stuck at the moment.

I've got an F# type which I'm trying to get to implement a c# interface

public interface ICrudService<T> where T: DelEntity, new()
{
    IEnumerable<T> GetAll();
}

here's how it's implemnted in c#:

public IEnumerable<T> GetAll()
{
    return repo.GetAll();
}

repo.GetAll returns an IQueryable, but the c# compiler knows enough to convert to IEnumerable because IQueryable<T> : IEnumerable<T>. but In F# the compiler can't work it and I've tried a few attempt to cast it correctly

type CrudService<'T when 'T :(new : unit -> 'T) and 'T :> DelEntity>(repo : IRepo<'T>) = 
    interface ICrudService<'T> with
         member this.GetAll () = 
            repo.GetAll<'T>

this is giving me a type mismatch error

What is the exact message? (Reading it could have let you suss it out yourself) — Ruben Bartelink, Jun 01 '14 at 20:34

score 7 · Accepted Answer · answered May 31 '14 at 18:14

7

You need to cast to IEnumerable<'T>:

type CrudService<'T when 'T :(new : unit -> 'T) and 'T :> DelEntity>(repo : IRepo<'T>) = 
        interface ICrudService<'T> with
             member this.GetAll () = 
                repo.GetAll() :> IEnumerable<'T>

answered May 31 '14 at 18:14

Lee

142,018
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1

That did it. I had tried the cast to IEnumerable, but what I was missing was the brackets after the function call on GetAll. – Jonny Cundall May 31 '14 at 23:08

score 1 · Answer 2 · answered May 31 '14 at 18:15

1

What if you used Seq.cast<'T? It sounds like it just needs to be casted to the correct Type. Since IEnumerables are implemented differently in F# than they are in C#.

let seqCast : seq<int> = Seq.cast repo.GetAll<'T>

answered May 31 '14 at 18:15

Johnathon Sullinger

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Get from IQueryable to IEnumerable

2 Answers2

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