chore: support for pre-filters in $vectorSearch MCP-240

[kmruiz]

Proposed changes

Adds support pre-filters in the aggregate tool, when using the $vectorSearch stage. We are also adding more matchers for better accuracy tests, namely:

• Matcher.caseInsensitiveString: for checking if a string is equal to another ignoring the case. Some LLMs can change the casing of values, and we don't have control over that unless the user specifically prompts for it, so for our tests, we will assume they are correct.
• Matcher.not: negates a matcher. For example, to ensure an array does not contain a specific value.
• Matcher.arrayOrSingle: Matches either [ value ] or value. This is important because MQL queries sometimes support both values.

Checklist

• I have signed the MongoDB CLA

[Copilot]

Pull Request Overview

This PR adds support for pre-filters in the $vectorSearch stage of the aggregate tool, along with new matcher utilities to improve accuracy test flexibility.

Key Changes:

• Enhanced $vectorSearch filter field description to distinguish between pre-filtering (using indexed filter fields) and post-filtering (using $match stages)
• Added three new matcher utilities: caseInsensitiveString for case-insensitive string comparisons, not for negating matchers, and arrayOrSingle for matching either array or single values
• Expanded accuracy tests to validate pre-filter and post-filter scenarios in vector search queries

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tests/accuracy/sdk/matcher.ts	Added new matcher classes (CaseInsensitiveStringMatcher, NotMatcher, ArrayOrSingleValueMatching) and corresponding factory methods
tests/accuracy/aggregate.test.ts	Added new test cases for pre-filter and post-filter scenarios, refactored common embedding parameters, and fixed typo "sci-fy" → "sci-fi"
src/tools/mongodb/read/aggregate.ts	Updated pipeline description with detailed guidance on pre-filtering vs post-filtering in $vectorSearch stages

[coveralls]

Pull Request Test Coverage Report for Build 18784361545

Details

• 18 of 23 (78.26%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.03%) to 80.105%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/common/search/embeddingsProvider.ts	14	19	73.68%

Totals
Change from base Build 18777096610:	-0.03%
Covered Lines:	6307
Relevant Lines:	7732

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💛 - Coveralls

[github-actions]

📊 Accuracy Test Results

📈 Summary

Metric	Value
Commit SHA	ff4d03cfa0293d05df11a5459bc65b3846f15d65
Run ID	62b757e2-8449-41c4-97a2-595be939d617
Status	done
Total Prompts Evaluated	100
Models Tested	1
Average Accuracy	92.2%
Responses with 0% Accuracy	7
Responses with 75% Accuracy	4
Responses with 100% Accuracy	91

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📎 Download Full HTML Report - Look for the accuracy-test-summary artifact for detailed results.

Report generated on: 10/24/2025, 4:13:07 PM