HighOrder EntityFramework

high_ef.fs

//how to implement CRUD with F# and entityframework and TypeClasses
     
//transform this into an highorder type
type Customer with static member queryId = <@ fun ( λ : Customer ) -> λ.Id @> 

//just a helper
type entity<'T> = ('T -> int)

//our highorder context
type EntitySet<'T when 'T : not struct> = {
    context : Entities
    getId : entity<'T>
} with
	member this.FindById id = <@ query { //we love AST, dont we?
		from entity in this.context.Set<'T> () do
		where ( (%this.queryId) entity = id )
		select entity } @> |> runQuery |> Seq.toList

//lets upgrade the boring entityframework to a kind of typeclass
let inline entitySet ( context : Entities ) ( template : ^T option ) = {   
    context = context
    getId = getId
    queryId = (^T : (static member queryId : Expr<('T -> int)>) ()) //almost like row polimorphism
}

//yes, this is MVC
let inline controller ( context : Entities ) ( operation : 'T Operation ) =
    let table = entitySet context None
    match operation with
    | Get ( Some id ) -> table.FindById id |> Seq.singleton
    | Get ( None ) -> table.List ()
    | Post ( entity ) -> table.AddOrUpdate entity; Seq.empty
    | Delete ( entity ) -> table.Delete entity; Seq.empty