typedesign.fs

/// The program is from http://codereview.stackexchange.com/q/20852
module Typedesign

type Metrics = 
  | Revenue
  | Volume
  | PriceAsp
  
  member m.FormatGroupings = 
    match m with
    | Revenue -> [ ("revenue", """$sum: { "$Amount" }" """) ]
    | Volume -> [ ("volume", """$sum: { "$Quantity" }" """) ]
    | PriceAsp -> List.append Revenue.FormatGroupings Volume.FormatGroupings
  
  member m.FormatProjections = 
    match m with
    | Revenue -> [ ("revenue", "$revenue") ]
    | Volume -> [ ("volume", "$volume") ]
    | PriceAsp -> [ ("priceAsp", """ $divide: ["$revenue", "$volume"]  """) ]

let buildQuery groupBy (metrics : Metrics list) = 
  let concatenate f = 
    let x = 
      metrics
      |> List.collect f
      |> List.map (fun m -> sprintf "{%s: %s}" (fst m) (snd m))
    System.String.Join(",", x)
  
  let groupings = concatenate (fun m -> m.FormatGroupings)
  let projections = concatenate (fun m -> m.FormatProjections)
  sprintf """{$group: {_id: {%s: "$%s"}}, %s}, $project: {%s}}""" groupBy 
    groupBy groupings projections