fix(mongodb): skip $$REMOVE check for required fields to enable index usage

[Kkartik14]

Description

Fixes prisma/prisma#29000

This PR fixes a critical performance issue where all MongoDB queries bypass indexes due to unconditional $$REMOVE checks.

Problem

Previously, every scalar filter in mongodb-query-connector was wrapped with:

{ $and: [<filter>, { $ne: ["$field", "$$REMOVE"] }] }

This forces MongoDB to use $expr (aggregation expressions), which cannot use indexes, causing full collection scans (COLLSCAN) on every query—including _id and @unique field lookups.

Root Cause

The exclude_undefineds() function was designed to handle optional fields that might be undefined in MongoDB documents. However, it was being called unconditionally for all fields, including:

• _id primary key (impossible to be missing)
• @unique required fields (have indexes that should be used)
• Required fields (Prisma enforces on create, cannot be missing)

Solution

Only add the $$REMOVE check for optional fields. Required fields and _id cannot be undefined by definition.

Added !field.is_required() condition before calling exclude_undefineds() in:

• default_scalar_filter() (line 278)
• insensitive_scalar_filter() (line 421)

Related Issues

• [MongoDB] All queries use $expr + $$REMOVE, bypassing indexes even for _id, @unique, and required fields prisma#29000 (main issue)
• Prisma is using $expr and $and in Mongo, resulting in the query by-passing indexes prisma#22878
• findFirstAndThrow on the primary key sometimes leads to a COLLSCAN when using mongodb prisma#23775
• MongoDB Connector generates queries which do not take advantage of indices. prisma#17396

[CLAassistant]

All committers have signed the CLA.

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing Kkartik14:fix/mongodb-index-bypass (e9f3bea) with main (56fb1a4)}

Summary

✅ 11 untouched benchmarks
⏩ 11 skipped benchmarks¹

Footnotes

1. 11 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩