From 6ebfea0f30a1d8ea24947380382969db616319cc Mon Sep 17 00:00:00 2001
From: Max Nowack <maxnowack@users.noreply.github.com>
Date: Mon, 11 Nov 2024 10:14:06 +0100
Subject: [PATCH] feat: allow specifying custom items merger for
 AutoFetchCollection

---
 docs/replication/index.md                    | 4 ++++
 packages/signaldb/src/AutoFetchCollection.ts | 5 ++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/docs/replication/index.md b/docs/replication/index.md
index 43ebbf1d..96f71b53 100644
--- a/docs/replication/index.md
+++ b/docs/replication/index.md
@@ -110,6 +110,10 @@ const Todos = new AutoFetchCollection({
   // If a persistence adapter is used, the data is loaded first and will be updated after the server data is fetched
   // If the data will be updated, the data will be saved to the persistence adapter and pushed to the server simultaneously
   persistence: createLocalStorageAdapter('todos'),
+
+  // Optionally you can also specify a mergeItems function to merge items
+  // if they're returned by multiple fetchQueryItems calls.
+  mergeItems: (itemA, itemB) => ({ ...itemA, ...itemB }),
 })
 
 // You can also observe the loading state of the collection.
diff --git a/packages/signaldb/src/AutoFetchCollection.ts b/packages/signaldb/src/AutoFetchCollection.ts
index 23083862..8cf43368 100644
--- a/packages/signaldb/src/AutoFetchCollection.ts
+++ b/packages/signaldb/src/AutoFetchCollection.ts
@@ -10,6 +10,7 @@ interface AutoFetchOptions<T extends { id: I } & Record<string, any>, I> {
   fetchQueryItems: (selector: Selector<T>) => ReturnType<ReplicatedCollectionOptions<T, I>['pull']>,
   purgeDelay?: number,
   registerRemoteChange?: (onChange: () => Promise<void>) => Promise<void>,
+  mergeItems?: (itemA: T, itemB: T) => T,
 }
 export type AutoFetchCollectionOptions<
   T extends BaseItem<I>,
@@ -35,6 +36,7 @@ export default class AutoFetchCollection<
   private reactivityAdapter: ReactivityAdapter | null = null
   private loadingSignals = new Map<string, Signal<boolean>>()
   private isFetchingSignal: Signal<boolean>
+  private mergeItems: (itemA: T, itemB: T) => T
 
   /**
    * @param options {Object} - Options for the collection.
@@ -54,7 +56,7 @@ export default class AutoFetchCollection<
               newItems.push(item)
               return
             }
-            newItems[index] = { ...newItems[index], ...item }
+            newItems[index] = this.mergeItems(newItems[index], item)
           })
           return newItems
         }, []),
@@ -64,6 +66,7 @@ export default class AutoFetchCollection<
         return Promise.resolve()
       },
     })
+    this.mergeItems = options.mergeItems ?? ((itemA, itemB) => ({ ...itemA, ...itemB }))
     this.purgeDelay = options.purgeDelay ?? 10000 // 10 seconds
     this.isFetchingSignal = createSignal(options.reactivity?.create(), false)
     if (!triggerRemoteChange) throw new Error('No triggerRemoteChange method found. Looks like your persistence adapter was not registered')