Geek asks and answers

Recursive Queries (F # 3.0)

I am trying to determine the type of Bill Of Materials queries using the recently introduced F # 3.0 query understanding syntax. Although such queries can be defined using yield!seq methods for in-memory collections, I haven’t lacked translating them into an understanding of queries intended for remote IQueryable sources. My guess is that the hard part will be to “train” the provider in recognizing common table expressions from recursive patterns.

Any ideas?

+3
source share
1 answer

, , F # 3.0 . , F # 3.0 IQueryable, #, .

, . F # SQL- ( ), - , FQ (), , , LINQ to SQL ( , , ).

, :

open System.IO
open Microsoft.FSharp.Quotations

type MyQueryBuilder() =
  member x.For(a, body) = Seq.collect body a
  member x.Quote(e) = e
  member x.YieldFrom(s) = s
  member x.Run(e:Expr<'T>) : 'T = failwithf "%A" e

// Example using the custom query builder
// (fails, printing the quoted query)
let mquery = MyQueryBuilder()    
let n = [1 .. 10]

let rec nums a : seq<int> =
  mquery { for b in n do
           yield! nums b }

Run , . MyQueryBuilder query - . query.Run ( IQueryable).

, , , , , , , - , , . , LINQ to SQL , , - , .

+5

More articles:


All Articles