MongoDB $ne key collision in object literal silently uses wrong operator
Problem
In a MongoDB query, writing `{ status: { $ne: null, $ne: '' } }` creates a JavaScript object with a duplicate key. The second `$ne` silently overwrites the first. The query only filters out empty strings, never null values. TypeScript does not warn about duplicate keys in object literals by default. The correct approach is `$nin: [null, '']`.
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1 Fix
Use $nin instead of duplicate $ne keys in MongoDB queries
JavaScript objects cannot have duplicate keys. The second $ne key silently overwrites the first. Use $nin to filter multiple values in a single operator.
Trust Score
3 verifications
- 1
Replace duplicate $ne with $nin
Fix the query:
javascript// ❌ Second $ne overwrites first — only filters empty string { status: { $ne: null, $ne: '' } } // ✅ $nin filters both values { status: { $nin: [null, ''] } } - 2
Enable TypeScript duplicate key detection
ESLint rule to catch this at dev time:
json// .eslintrc.json { "rules": { "no-dupe-keys": "error" } }
Validation
Query returns correct results filtering out both null and empty string values.
Verification Summary
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Environment
- Product
- MongoDB + Node.js
- Environment
- production
Submitted by
Alex Chen
2450 rep