From 29297bba6310c0eded6b674385299d777c9ca9d8 Mon Sep 17 00:00:00 2001
From: koresar <kore.sar@gmail.com>
Date: Wed, 15 May 2024 21:30:57 +1000
Subject: [PATCH] fix: use "_id" index hint for balance re-calc only of that ID
 was a recent one

---
 src/Book.ts | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/Book.ts b/src/Book.ts
index 8d1a5e4..f34a81b 100644
--- a/src/Book.ts
+++ b/src/Book.ts
@@ -109,7 +109,13 @@ export class Book<U extends ITransaction = ITransaction, J extends IJournal = IJ
 
     const partialBalanceOptions = { ...options };
     // If using a balance snapshot then make sure to use the appropriate (default "_id_") index for the additional balance calc.
-    if (parsedQuery._id) partialBalanceOptions.hint =  { _id: 1 };
+    if (parsedQuery._id && balanceSnapshot) {
+      const lastTransactionDate =  balanceSnapshot.transaction.getTimestamp();
+      if (lastTransactionDate.getTime() + this.expireBalanceSnapshotSec * 1000 > Date.now()) {
+        // last transaction for this balance was just recently, then let's use the "_id" index as it will likely be faster than any other.
+        partialBalanceOptions.hint =  { _id: 1 };
+      }
+    }
     const result = (await transactionModel.collection.aggregate([match, GROUP], partialBalanceOptions).toArray())[0];
 
     let balance = 0;