add a sequence number to transactions for sorting

Author: samwillis

.changeset/khaki-cougars-give.md

@@ -0,0 +1,5 @@
+---
+"@tanstack/db": patch
+---
+
+add a sequence number to transactions to when sorting we can ensure that those created in the same ms are sorted in the correct order

packages/db/src/collection.ts

@@ -277,8 +277,8 @@ export class CollectionImpl<
       throw new Error(`Collection requires a sync config`)
     }
 
-    this.transactions = new SortedMap<string, Transaction<any>>(
-      (a, b) => a.createdAt.getTime() - b.createdAt.getTime()
+    this.transactions = new SortedMap<string, Transaction<any>>((a, b) =>
+      a.compareCreatedAt(b)
     )
 
     this.config = config

packages/db/src/transactions.ts

@@ -12,6 +12,8 @@ import type {
 const transactions: Array<Transaction<any>> = []
 let transactionStack: Array<Transaction<any>> = []
 
+let sequenceNumber = 0
+
 export function createTransaction<
   TData extends object = Record<string, unknown>,
 >(config: TransactionConfig<TData>): Transaction<TData> {
@@ -54,6 +56,7 @@ export class Transaction<
   public isPersisted: Deferred<Transaction<T, TOperation>>
   public autoCommit: boolean
   public createdAt: Date
+  public sequenceNumber: number
   public metadata: Record<string, unknown>
   public error?: {
     message: string
@@ -71,6 +74,7 @@ export class Transaction<
     this.isPersisted = createDeferred<Transaction<T, TOperation>>()
     this.autoCommit = config.autoCommit ?? true
     this.createdAt = new Date()
+    this.sequenceNumber = sequenceNumber++
     this.metadata = config.metadata ?? {}
   }
 
@@ -200,4 +204,19 @@ export class Transaction<
 
     return this
   }
+
+  /**
+   * Compare two transactions by their createdAt time and sequence number in order
+   * to sort them in the order they were created.
+   * @param other - The other transaction to compare to
+   * @returns -1 if this transaction was created before the other, 1 if it was created after, 0 if they were created at the same time
+   */
+  compareCreatedAt(other: Transaction<any>): number {
+    const createdAtComparison =
+      this.createdAt.getTime() - other.createdAt.getTime()
+    if (createdAtComparison !== 0) {
+      return createdAtComparison
+    }
+    return this.sequenceNumber - other.sequenceNumber
+  }
 }