In-memory Drain abstractions applied to A Functional Architecture with F#
This post shows how to apply the Drain filter abstraction to the master branch of the Pluralsight course about A Functional Architecture with F# by Mark Seemann.
As the diff-output shows, applying filtering with Drains cuts the maintenance of multiple homogenous abstractions, and makes the code cleaner and easier to reason about.
(Also available as a GitHub Gist.)
diff --git a/BookingApi/DomainModel.fs b/BookingApi/DomainModel.fs
index 4a4260f..c2079cf 100644
--- a/BookingApi/DomainModel.fs
+++ b/BookingApi/DomainModel.fs
@@ -7,6 +7,23 @@ type Period =
| Month of int * int
| Day of int * int * int
+[<AutoOpen>]
+module Drain =
+ type IDrainable<'a, 'b> =
+ inherit seq<'a>
+ abstract On : 'b -> seq<'a>
+
+ let on x (d : IDrainable<'a, 'b>) = d.On x
+
+ let ofSeq areEqual s =
+ { new IDrainable<'a, 'b> with
+ member this.On x = s |> Seq.filter (fun y -> areEqual y x)
+ member this.GetEnumerator() = s.GetEnumerator()
+ member this.GetEnumerator() =
+ (this :> 'a seq).GetEnumerator() :> System.Collections.IEnumerator }
+
+ let empty<'a, 'b> = Seq.empty<'a> |> ofSeq (fun x (y : 'b) -> false)
+
module Dates =
let InitInfinite (date : DateTime) =
date |> Seq.unfold (fun d -> Some(d, d.AddDays 1.0))
@@ -30,24 +47,11 @@ module Dates =
module Reservations =
- type IReservations =
- inherit seq<Envelope<Reservation>>
- abstract Between : DateTime -> DateTime -> seq<Envelope<Reservation>>
-
- type ReservationsInMemory(reservations) =
- interface IReservations with
- member this.Between min max =
- reservations
- |> Seq.filter (fun r -> min <= r.Item.Date && r.Item.Date <= max)
- member this.GetEnumerator() =
- reservations.GetEnumerator()
- member this.GetEnumerator() =
- (this :> seq<Envelope<Reservation>>).GetEnumerator() :> System.Collections.IEnumerator
-
- let ToReservations reservations = ReservationsInMemory(reservations)
+ let ToReservations reservations =
+ reservations |> Drain.ofSeq (fun x y -> x.Item.Date >= fst y && x.Item.Date <= snd y)
- let Between min max (reservations : IReservations) =
- reservations.Between min max
+ let Between min max (reservations : IDrainable<Envelope<Reservation>, DateTime * DateTime>) =
+ reservations |> Drain.on(min, max)
let On (date : DateTime) reservations =
let min = date.Date
@@ -73,18 +77,8 @@ module Reservations =
module Notifications =
- type INotifications =
- inherit seq<Envelope<Notification>>
- abstract About : Guid -> seq<Envelope<Notification>>
-
- type NotificationsInMemory(notifications : Envelope<Notification> seq) =
- interface INotifications with
- member this.About id =
- notifications |> Seq.filter (fun n -> n.Item.About = id)
- member this.GetEnumerator() = notifications.GetEnumerator()
- member this.GetEnumerator() =
- (this :> Envelope<Notification> seq).GetEnumerator() :> System.Collections.IEnumerator
-
- let ToNotifications notifications = NotificationsInMemory(notifications)
-
- let About id (notifications : INotifications) = notifications.About id
+ let ToNotifications notifications =
+ notifications |> Drain.ofSeq (fun x y -> x.Item.About = y)
+
+ let About id (notifications : IDrainable<Envelope<Notification>, Guid>) =
+ notifications |> Drain.on id
diff --git a/BookingApi/Controllers.fs b/BookingApi/Controllers.fs
index 2234ae0..986c5a9 100644
--- a/BookingApi/Controllers.fs
+++ b/BookingApi/Controllers.fs
@@ -41,7 +41,7 @@ type ReservationsController() =
if disposing then subject.Dispose()
base.Dispose disposing
-type NotificationsController(notifications : Notifications.INotifications) =
+type NotificationsController(notifications) =
inherit ApiController()
member this.Get id =
@@ -61,7 +61,7 @@ type NotificationsController(notifications : Notifications.INotifications) =
member this.Notifications = notifications
-type AvailabilityController(reservations : Reservations.IReservations,
+type AvailabilityController(reservations,
seatingCapacity : int) =
inherit ApiController()
diff --git a/BookingApi/Infrastructure.fs b/BookingApi/Infrastructure.fs
index 18867a8..7082d19 100644
--- a/BookingApi/Infrastructure.fs
+++ b/BookingApi/Infrastructure.fs
@@ -9,7 +9,7 @@ open System.Reactive
open FSharp.Reactive
open Ploeh.Samples.Booking.HttpApi.Reservations
-type CompositionRoot(reservations : IReservations,
+type CompositionRoot(reservations,
notifications,
reservationRequestObserver,
seatingCapacity) =
diff --git a/BookingApi.UnitTests/TestDsl.fs b/BookingApi.UnitTests/TestDsl.fs
index df09626..cde8e4d 100644
--- a/BookingApi.UnitTests/TestDsl.fs
+++ b/BookingApi.UnitTests/TestDsl.fs
@@ -37,19 +37,20 @@ type DateStringCustomization() =
(context.Resolve typeof<DateTime> :?> DateTime).ToString "yyyy.MM.dd" :> obj
| _ -> NoSpecimen(request) :> obj }
+open Ploeh.Samples.Booking.HttpApi
+open Ploeh.Samples.Booking.HttpApi.Notifications
+
type NotificationsCustomization() =
interface ICustomization with
member this.Customize fixture =
- fixture.Customizations.Add(
- TypeRelay(
- typeof<Ploeh.Samples.Booking.HttpApi.Notifications.INotifications>,
- typeof<Ploeh.Samples.Booking.HttpApi.Notifications.NotificationsInMemory>))
-
+ let notifications =
+ fixture.CreateMany<Envelope<Notification>>() |> ToNotifications
+ fixture.Inject notifications
+
type ReservationsCustomization() =
interface ICustomization with
member this.Customize fixture =
- fixture.Inject<Ploeh.Samples.Booking.HttpApi.Reservations.IReservations>(
- [] |> Ploeh.Samples.Booking.HttpApi.Reservations.ToReservations)
+ fixture.Inject Drain.empty<Envelope<Reservation>, DateTime * DateTime>
type TestConventions() =
inherit CompositeCustomization(
diff --git a/BookingApi.UnitTests/DomainModelTests.fs b/BookingApi.UnitTests/DomainModelTests.fs
index 221e560..c021706 100644
--- a/BookingApi.UnitTests/DomainModelTests.fs
+++ b/BookingApi.UnitTests/DomainModelTests.fs
@@ -92,14 +92,10 @@ module DatesTests =
module ReserverationsTests =
open Reservations
-
- [<Theory; TestConventions>]
- let ReservationsInMemoryAreReservations (sut : ReservationsInMemory) =
- Assert.IsAssignableFrom<IReservations>(sut)
[<Theory; TestConventions>]
let ToReservationsReturnsCorrectResult (expected : Envelope<Reservation> seq) =
- let actual : ReservationsInMemory = expected |> ToReservations
+ let actual = expected |> ToReservations
Assert.Equal<Envelope<Reservation>>(expected, actual)
[<Theory; TestConventions>]
@@ -111,7 +107,7 @@ module ReserverationsTests =
let expected = reservations |> Seq.skip 2 |> Seq.take 6
let sut = reservations |> ToReservations
- let actual = (sut :> IReservations).Between min.Item.Date max.Item.Date
+ let actual = sut |> Drain.on(min.Item.Date, max.Item.Date)
Assert.Equal<Envelope<Reservation>>(expected, actual)
@@ -125,7 +121,7 @@ module ReserverationsTests =
let actual = sut |> Between min.Item.Date max.Item.Date
- let expected = (sut :> IReservations).Between min.Item.Date max.Item.Date
+ let expected = sut |> Drain.on(min.Item.Date, max.Item.Date)
Assert.Equal<Envelope<Reservation>>(expected, actual)
[<Theory; TestConventions>]
@@ -203,12 +199,8 @@ module NotificationsTest =
open Notifications
[<Theory; TestConventions>]
- let NotificationsInMemoryAreNotifications (sut : NotificationsInMemory) =
- Assert.IsAssignableFrom<INotifications> sut
-
- [<Theory; TestConventions>]
let ToNotificationsReturnsCorrectResult (expected : Envelope<Notification> seq) =
- let actual : NotificationsInMemory = expected |> ToNotifications
+ let actual = expected |> ToNotifications
Assert.Equal<Envelope<Notification>>(expected, actual)
[<Theory; TestConventions>]
@@ -219,7 +211,7 @@ module NotificationsTest =
let expected = notifications |> PickRandom
let sut = notifications |> ToNotifications
- let actual = (sut :> INotifications).About expected.Item.About
+ let actual = sut |> Drain.on expected.Item.About
Assert.Equal(1, actual |> Seq.length)
Assert.Equal(expected, actual |> Seq.head)
@@ -232,7 +224,7 @@ module NotificationsTest =
let sut = generator |> Seq.take 10 |> Seq.toList |> ToNotifications
Assert.False(sut |> Seq.exists (fun n -> n.Item.About = about))
- let actual = (sut :> INotifications).About about
+ let actual = sut |> Drain.on about
Assert.True(actual |> Seq.isEmpty)
@@ -241,7 +233,7 @@ module NotificationsTest =
let sut = notifications |> ToNotifications
let about = (sut |> Seq.toList |> PickRandom).Item.About
- let actual : Envelope<Notification> seq = sut |> About about
+ let actual = sut |> About about
- let expected = (sut :> INotifications).About about
+ let expected = sut |> Drain.on about
Assert.Equal<Envelope<Notification>>(expected, actual)
diff --git a/BookingApi.UnitTests/ControllerTests.fs b/BookingApi.UnitTests/ControllerTests.fs
index 166278e..05f9363 100644
--- a/BookingApi.UnitTests/ControllerTests.fs
+++ b/BookingApi.UnitTests/ControllerTests.fs
@@ -79,11 +79,11 @@ module NotificationsControllerTests =
[<Theory; TestConventions>]
let NotificationsAreExposedForExpection
- ([<Frozen>]expected : Notifications.INotifications)
+ ([<Frozen>]expected : IDrainable<Envelope<Notification>, Guid>)
(sut : NotificationsController) =
- let actual : Notifications.INotifications = sut.Notifications
- Assert.Equal<Notifications.INotifications>(expected, actual)
+ let actual = sut.Notifications
+ Assert.Equal<IDrainable<Envelope<Notification>, Guid>>(expected, actual)
[<Theory; TestConventions>]
let GetWithoutMatchingNotificationReturnsCorrectResult
@@ -187,7 +187,7 @@ module AvailabilityControllerTests =
yearsInFuture : int) =
// Fixture setup
let reservations = mutableReservations |> Reservations.ToReservations
- fixture.Inject<Reservations.IReservations> reservations
+ fixture.Inject reservations
let sut =
fixture.Generate<AvailabilityController>()
|> Seq.filter (fun c -> c.SeatingCapacity > 1)
@@ -284,7 +284,7 @@ module AvailabilityControllerTests =
yearsInFuture : int) =
// Fixture setup
let reservations = mutableReservations |> Reservations.ToReservations
- fixture.Inject<Reservations.IReservations> reservations
+ fixture.Inject reservations
let sut =
fixture.Generate<AvailabilityController>()
|> Seq.filter (fun c -> c.SeatingCapacity > 1)
@@ -395,7 +395,7 @@ module AvailabilityControllerTests =
yearsInFuture : int) =
// Fixture setup
let reservations = mutableReservations |> Reservations.ToReservations
- fixture.Inject<Reservations.IReservations> reservations
+ fixture.Inject reservations
let sut =
fixture.Generate<AvailabilityController>()
|> Seq.filter (fun c -> c.SeatingCapacity > 1)
To apply the diff, access the source code by getting a Pluralsight subscription which is totally worth it for this course.