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feat(EventStoreDb): Add AccessStrategy.CustomOrigin #222

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feat(EventStoreDb): Add AccessStrategy.CustomOrigin #222

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12 changes: 7 additions & 5 deletions src/Equinox.EventStore/EventStore.fs
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Original file line number Diff line number Diff line change
Expand Up @@ -446,6 +446,9 @@ type AccessStrategy<'event,'state> =
/// Scanning for events concludes when any event passes the <c>isOrigin</c> test.
/// See https://eventstore.org/docs/event-sourcing-basics/rolling-snapshots/index.html
| RollingSnapshots of isOrigin : ('event -> bool) * toSnapshot : ('state -> 'event)
/// Customize the loading process, walking events toward the the oldest one (in batches)
/// Short-circuits if the supplied `isOrigin` identifies the given event as being a valid alternate starting point
| CustomOrigin of isOrigin : ('event -> bool)

type private CompactionContext(eventsLen : int, capacityBeforeCompaction : int) =
/// Determines whether writing a Compaction event is warranted (based on the existing state and the current accumulated changes)
Expand All @@ -456,22 +459,21 @@ type private Category<'event, 'state, 'context>(context : Context, codec : FsCod

let compactionPredicate =
match access with
| None -> None
| None | Some (AccessStrategy.CustomOrigin _) -> None
| Some AccessStrategy.LatestKnownEvent -> Some (fun _ -> true)
| Some (AccessStrategy.RollingSnapshots (isValid, _)) -> Some isValid

let isOrigin =
match access with
| None | Some AccessStrategy.LatestKnownEvent -> fun _ -> true
| Some (AccessStrategy.RollingSnapshots (isValid, _)) -> isValid
| Some (AccessStrategy.RollingSnapshots (isValid, _)) | Some (AccessStrategy.CustomOrigin isValid) -> isValid

let loadAlgorithm load streamName initial log =
let batched = load initial (context.LoadBatched streamName log (tryDecode,None))
let compacted = load initial (context.LoadBackwardsStoppingAtCompactionEvent streamName log (tryDecode, isOrigin))
match access with
| None -> batched
| Some AccessStrategy.LatestKnownEvent
| Some (AccessStrategy.RollingSnapshots _) -> compacted
| Some AccessStrategy.LatestKnownEvent | Some (AccessStrategy.RollingSnapshots _) | Some (AccessStrategy.CustomOrigin _) -> compacted

let load (fold : 'state -> 'event seq -> 'state) initial f = async {
let! token, events = f
Expand All @@ -489,7 +491,7 @@ type private Category<'event, 'state, 'context>(context : Context, codec : FsCod
let encode e = codec.Encode(ctx, e)
let events =
match access with
| None | Some AccessStrategy.LatestKnownEvent -> events
| None | Some AccessStrategy.LatestKnownEvent | Some (AccessStrategy.CustomOrigin _) -> events
| Some (AccessStrategy.RollingSnapshots (_, compact)) ->
let cc = CompactionContext(List.length events, pos.batchCapacityLimit.Value)
if cc.IsCompactionDue then events @ [fold state events |> compact] else events
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