Multi-select filter returns incorrect number of features when multiple values are selected

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#4,574 opened on Jul 1, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 58/100

Issue type: Bug
Clarity: Clearly specified
Activity status: Quiet
Tech stack: android, cpp, ios
Domain: mobile

Research direction

Reproduce the issue in the Mergin Maps mobile app using project tester-ws-1/test_feature_filtering, then trace the Filters flow for the multi-select-photo_survey-Favorite cities filter into the photo_survey features list. Compare the filtering behavior for Vienna and Prague with the QGIS attribute table. Done means all three features containing either selected value are shown on Android and iOS.

Written by the indexing model from the issue text.

Description

android 🤖 bug filtering iOS 🍎

Description

When a multi-select filter is configured on an array-type text field (e.g. "Favorite cities") and the user selects multiple values (e.g. Vienna and Prague), the filtered feature list shows fewer results than expected. Features containing either of the selected values should all be returned.

Environment
[x] Staging [ ] PROD

Application (+ app version, build, operating system)

Mergin Maps mobile 2026.3.0, Android 16 (Pixel 9)
Mergin Maps mobile 2026.3.0, iOS 26.0

Steps to reproduce

Clone and open project tester-ws-1/test_feature_filtering in the mobile app
Open Filters → select filter Multi select-photo_survey-Favorite cities
Select values: Vienna and Prague
Tap Apply filters
Open the photo_survey features list

Actual results

2 features are shown.

Expected results

3 features are shown — all features whose "Favorite cities" field contains Vienna or Prague:

Monica Geller — {Bratislava, Vienna}
Chandler Bing — {Bratislava, Prague}
Janice Hosenb... — {Budapest, Helsinki, Prague}

Screenshots or logs

QGIS attribute table confirming expected 3 matching features: (see attached)

Conclusion
Created by Claude and supervised by a human test analyst.

Dominant language: C++
Stars: 388
Forks: 87
Avg merge: 4d 1h
Merged PRs (30d): 23

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