MONGOID-5924 Add support for flat indexing method in vector search#6152
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…dex definitions - Add `exact: false` parameter to `vector_search` (class and instance) so callers can request exact nearest-neighbor search; when true, numCandidates is omitted from the $vectorSearch stage, matching the behavior already present in auto_embed_search. - Validate at index-definition time that hnswOptions is not combined with indexingMethod: flat, per the Atlas Vector Search spec. - Document the flat indexing method in the vector_search_index DSL.
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Pull request overview
This PR adds support for flat vector search indexes and exposes exact: search behavior for vector search APIs.
Changes:
- Adds
exact:keyword support to class-level and instance-levelvector_search. - Adds validation preventing
hnswOptionswithindexingMethod: 'flat'. - Adds unit coverage for flat index validation and vector search pipeline construction.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
lib/mongoid/search_indexable.rb |
Updates vector search API, pipeline construction, validation, and documentation. |
spec/mongoid/search_indexable_spec.rb |
Adds tests for flat indexing validation and exact vector search pipeline behavior. |
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- Send exact: true to the $vectorSearch stage when exact: true is passed, matching the auto_embed_search behavior; previously only numCandidates was being omitted but the exact flag was never forwarded to MongoDB. - Add missing @param entry for exact: on the instance-level vector_search YARD block.
comandeo-mongo
approved these changes
Jun 8, 2026
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exact: falseparameter tovector_search(both class-level and instance-level), consistent with the existingauto_embed_searchAPI. Whenexact: true,numCandidatesis omitted from the$vectorSearchaggregation stage — required for exact nearest-neighbor search and correct behavior with flat indexes.hnswOptionsis not combined withindexingMethod: 'flat', per the Atlas Vector Search spec error table.indexingMethod: 'flat'in thevector_search_indexDSL with an example.The
indexingMethodfield itself already passed through the definition hash unchanged, so no DSL changes were needed for index creation. Per the spec,numCandidatesis accepted but ignored by the server for flat indexes, so Mongoid does not strip it automatically — users opt in to exact search viaexact: true.