Latest Mongoose Version (as of now)

As of my latest training data (Oct 2024), the current major version of Mongoose is 9.x. The exact patch version (e.g. 9.0.3, 9.1.0) can change frequently, so you should always check with:

1npm view mongoose version

1npm view mongoose version

or in your project:

1npm ls mongoose

1npm ls mongoose

Your statement that the latest version is 9.* and that it introduces more strict types and features like QueryFilter is directionally correct: Mongoose 9 continues the trend of tightening TypeScript support and improving type safety, which can indeed cause breaking changes in existing code.

Why your code might be breaking

Common reasons code breaks when upgrading to Mongoose 9 include:

1. Stricter TypeScript types

   • Queries, filters, and updates are now more strongly typed.
   • Things that were allowed before (e.g., using arbitrary fields, incorrect value types, or loose query objects) may now cause:
     • TypeScript errors at compile time
     • Runtime errors if they violate schema expectations

2. Stricter QueryFilter / query typing

   • Filters passed to methods like find, findOne, updateOne, etc. are now more tightly constrained to your schema.
   • Using untyped/loose objects may require:
     • Casting (e.g., as any or as QueryFilter<MyDocument>)
     • Updating your schema types and interfaces to match actual usage

3. Potential changes to default behaviors

   • Some defaults (like strict mode, casting behavior, or deprecation removals) may have changed between 6/7/8 and 9.
   • Features deprecated in earlier versions may be removed in 9, breaking older patterns.

How to move forward

1. Check the official Mongoose 9 changelog / migration guide
   On the Mongoose GitHub repo or documentation site, look specifically for:

   • “Breaking Changes” for v9
   • Migration notes from your previous major version (e.g. v7 → v8 → v9)

2. Narrow down the breakage

   • Look at the exact TypeScript or runtime errors you’re seeing.
   • Pay special attention to:
     • Query filters (Model.find({ ... }), Model.updateOne({ ... }))
     • Middleware hooks
     • Lean queries, population, and custom types

3. Adjust your types

   • Ensure your document interfaces/types match your schema fields.
   • If needed, wrap some places with explicit generics or as const / as any while you gradually tighten types properly.

If you share a small snippet of the code that’s breaking (query, schema, and the error message), I can point out exactly what changed in Mongoose 9 that affects it and how to fix it.