BE: add 'in' operator to MetadataFilter for categorical filtering

[ikondrat]

Summary

Stacked on p3.

Adds an in operator to MetadataFilter so the frontend can request samples matching any of a set of categorical values (including null/missing):

• Validates the list is non-empty and homogeneous (all str, all bool, or [None] / [str | None])
• Builds an OR predicate via a standard SQL IN clause for non-null values
• When None is included, uses a LEFT OUTER JOIN so samples with no metadata entry for the field are also matched

Also includes a mypy # type: ignore[no-untyped-call] fix for query.compile(dialect=postgresql.dialect()) in test_metadata_filter.py, matching the pattern used in other test files.

Test plan

• make static-checks passes
• make test-ci passes (new tests in test_metadata_filter.py and test_sample_metadata_filtering.py, plus additional API tests in test_metadata.py)

Part of LIG-9585.

Summary by CodeRabbit

• New Features

  • Added support for categorical metadata filtering with the in operator.
  • Filters can match multiple string or boolean values, including samples with missing metadata.
  • Invalid empty in filter lists now return a validation error.

• Tests

  • Added coverage for valid and invalid categorical filters, missing metadata, and special-character metadata keys.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: fd451be5-30ec-407f-a9fd-d0ced6beb1c0

📥 Commits

Reviewing files that changed from the base of the PR and between b5b97e0 and ce881ab.

📒 Files selected for processing (5)

• lightly_studio/src/lightly_studio/resolvers/metadata_resolver/metadata_filter.py
• lightly_studio/src/lightly_studio/resolvers/metadata_resolver/sample/__init__.py
• lightly_studio/tests/api/routes/api/test_metadata.py
• lightly_studio/tests/resolvers/metadata_resolvers/sample/test_sample_metadata_filtering.py
• lightly_studio/tests/resolvers/metadata_resolvers/test_metadata_filter.py

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📝 Walkthrough

Walkthrough

Changes

Metadata filtering

Layer / File(s)	Summary
Filter operator contract and validation lightly_studio/src/lightly_studio/resolvers/metadata_resolver/metadata_filter.py, lightly_studio/tests/resolvers/metadata_resolvers/test_metadata_filter.py, lightly_studio/tests/api/routes/api/test_metadata.py	Adds the in operator, validates non-empty homogeneous string or boolean lists with optional nulls, and returns HTTP 422 for invalid values.
SQL predicate construction lightly_studio/src/lightly_studio/resolvers/metadata_resolver/metadata_filter.py, lightly_studio/src/lightly_studio/resolvers/metadata_resolver/sample/__init__.py, lightly_studio/tests/resolvers/metadata_resolvers/test_metadata_filter.py	Builds categorical IN predicates, normalizes booleans, handles null metadata through outer joins and IS NULL, and preserves special-character keys.
Endpoint and sample filtering coverage lightly_studio/tests/api/routes/api/test_metadata.py, lightly_studio/tests/resolvers/metadata_resolvers/sample/test_sample_metadata_filtering.py	Verifies resolver calls and filtering for concrete values, booleans, missing metadata, and special-character metadata keys.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant APIClient
  participant MetadataValueCountsAPI
  participant MetadataFilter
  participant apply_metadata_filters
  participant PostgreSQL
  APIClient->>MetadataValueCountsAPI: submit metadata/value-counts request
  MetadataValueCountsAPI->>MetadataFilter: validate filter
  MetadataValueCountsAPI->>apply_metadata_filters: apply validated filters
  apply_metadata_filters->>PostgreSQL: execute IN or NULL predicate
  PostgreSQL-->>MetadataValueCountsAPI: return matching rows

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Possibly related PRs

• lightly-ai/lightly-studio#1682: Related categorical metadata filtering and MetadataFilter behavior.

Suggested reviewers: gabrielfruet, horatiualmasan, igorsusmelj

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the main change: adding an "in" operator to MetadataFilter for categorical filtering.
Description check	✅ Passed	The description covers the change and test plan, but it should add the changelog checkbox section to match the template.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch kondrat-lig-9585-frontend-categorical-metadata-bar-chart-filter-ui-8-sp.p4

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[lightly-fast-track-bot]

❌  Fast Track: checks did not pass

Guardrail	Result	Message
dummy	✅	Always passes.
frontend/complexity	✅	0 file(s) checked.
backend/complexity	✅	5 file(s) checked, no violations.
backend/coverage	❌	Guardrail threw: Command failed: uv run pytest tests/resolvers/metadata_resolvers/test_metadata_filter.py --cov=src/lightly_studio/resolvers/metadata_resolver --cov-report=json:coverage.json -q --no-header ImportError while loading conftest '/home/runner/work/lightly-studio/lightly-studio/lightly_studio/tests/conftest.py'. tests/conftest.py:18: in from lightly_studio.api import features src/lightly_studio/init.py:18: in from lightly_studio.core.start_gui import ( src/lightly_studio/core/start_gui.py:12: in from lightly_studio.api.server import Server src/lightly_studio/api/server.py:11: in from lightly_studio.api.app import app src/lightly_studio/api/app.py:16: in from lightly_studio.api.routes import ( src/lightly_studio/api/routes/webapp.py:19: in raise RuntimeError(f"Directory '{webapp_dir}' does not exist in '{project_root}'") E RuntimeError: Directory '/home/runner/work/lightly-studio/lightly-studio/lightly_studio/src/lightly_studio/dist_lightly_studio_view_app' does not exist in '/home/runner/work/lightly-studio/lightly-studio/lightly_studio/src/lightly_studio'
diff-size	❌	PR adds 227 line(s), which exceeds the limit of 215.
frontend/coverage	✅	0 file(s) checked.

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_{Reflects ce881ab.}

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[ikondrat]

/review