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AzureDocumentDB: fix CosineDistance scores and score threshold, support CosineSimilarity - #78
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adamsitnik merged 3 commits intoOct 28, 2026
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…hreshold keeps distances up to it COS returns the cosine similarity. With CosineDistance, the default, the provider returned that similarity as the score and kept scores >= ScoreThreshold. It now returns 1 - similarity and keeps distances <= ScoreThreshold, as InMemory does. The distance function conformance tests now check the scores.
COS returns the cosine similarity, so CosineSimilarity maps to it with the score as it is and keeps scores >= ScoreThreshold. Chroma, InMemory, PgVector and Redis already take both CosineSimilarity and CosineDistance. Co-authored-by: Empiree <Empiree@users.noreply.github.com>
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🟢 Approval recommended
Static review found no blocking issues in the focused scoring changes or regression coverage; tests were not executed during review.
No open issues 🎉
What changed in this PR
Fixes #72 by aligning AzureDocumentDB’s cosine-distance scores and thresholds with other vector-store providers, while adding explicit cosine-similarity support.
Changes:
- Converts cosine similarity to distance and translates distance thresholds into equivalent similarity filters.
- Supports
CosineSimilaritythrough the COS index metric and bumps the provider to 1.1.0. - Adds unit coverage and enables conformance checks for scores and cosine similarity.
| File | Description |
|---|---|
| MEVD/test/AzureDocumentDB.UnitTests/DocumentDBCollectionTests.cs | Updates the expected search score to cosine distance. |
| MEVD/test/AzureDocumentDB.UnitTests/DocumentDBCollectionDistanceFunctionTests.cs | Adds index, score, and threshold mapping tests. |
| MEVD/test/AzureDocumentDB.ConformanceTests/DocumentDBDistanceFunctionTests.cs | Enables score assertions and cosine-similarity tests. |
| MEVD/src/AzureDocumentDB/DocumentDBCollectionSearchMapping.cs | Converts scores and translates cosine-distance thresholds. |
| MEVD/src/AzureDocumentDB/DocumentDBCollectionCreateMapping.cs | Maps cosine similarity to COS. |
| MEVD/src/AzureDocumentDB/DocumentDBCollection.cs | Applies score conversion using the selected vector property. |
| MEVD/src/AzureDocumentDB/AzureDocumentDB.csproj | Updates the provider version to 1.1.0. |
Review effort: Balanced
adamsitnik
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Oct 28, 2026
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The changes look great, thank you @Laurianti !
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Fixes #72.
Fix
CosineDistance, the default. COS returns the cosine similarity, and the provider returned it as the score, so the best match had the highest score.ScoreThresholdkept scores>=the threshold, so a threshold on the distance dropped the closest records. Now the score is1 - similarityandScoreThresholdkeeps distances<=it, as InMemory does. In the repro of AzureDocumentDB: CosineDistance returns similarity scores, and ScoreThreshold filters the wrong way #72: scores 0, 1, 2, andScoreThreshold = 1.5keepssameandorthogonal.Changes
CosineSimilaritymaps to COS, with the score as it is andScoreThresholdas a minimum, as on Chroma, InMemory, PgVector and Redis, which take bothCosineSimilarityandCosineDistance. Before, it threwNotSupportedException.Tests
SearchReturnsRecordWithScoreAsyncnow expects the distance, and fails without the fix too.CosineSimilarity. Without the fix,CosineDistancefails on the scores andCosineSimilaritythrows.documentdb-local: 215 passed on net10.0 and 213 on net472.