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Troubleshooting Guide

Common issues and solutions for FilterMate.

Installation Issues​

Plugin Not Visible in QGIS​

Symptoms:

  • FilterMate not in Plugin menu
  • Not listed in Plugin Manager

Solutions:

  1. Check installation:

    # Linux
    ls ~/.local/share/QGIS/QGIS3/profiles/default/python/plugins/filter_mate

    # Windows
    dir %APPDATA%\QGIS\QGIS3\profiles\default\python\plugins\filter_mate

  2. Verify metadata.txt exists

  3. Enable in Plugin Manager:

    • Plugins → Manage and Install Plugins
    • Installed tab
    • Check "FilterMate"

  4. Restart QGIS

Import Errors on Startup​

Error:

ModuleNotFoundError: No module named 'psycopg2'

Solution: psycopg2 is optional. If you don't use PostgreSQL:

  1. Open config/config.json
  2. Set "POSTGRESQL_AVAILABLE": false
  3. Restart QGIS

To install psycopg2:

pip install psycopg2-binary

Connection Issues​

PostgreSQL Connection Failed​

Symptoms:

  • "Cannot connect to database"
  • "Connection refused"

Solutions:

  1. Check PostgreSQL is running:

    sudo systemctl status postgresql

  2. Verify connection parameters:

    • Host: correct address
    • Port: default 5432
    • Database: exists
    • User: has permissions

  3. Test connection in QGIS:

    • Layer → Add Layer → Add PostGIS Layer
    • Try connecting directly

  4. Check psycopg2 installation:

    # In QGIS Python Console
    import psycopg2
    print(psycopg2.__version__)

Spatialite Database Locked​

Error:

sqlite3.OperationalError: database is locked

Causes:

  • Another process using database
  • QGIS project auto-save
  • Incomplete previous operation

Solutions:

  1. Automatic retry (built-in):

    • FilterMate retries 5 times automatically
    • Wait a few seconds

  2. Close other connections:

    • Close other QGIS projects using same database
    • Check DB Browser for SQLite

  3. Restart QGIS:

    • Save project
    • Restart QGIS
    • Reopen project

Project Loading Issues​

Layers Not Loading After Project Change​

Symptoms:

  • Plugin dockwidget empty after switching projects
  • Layers present in project but not showing in FilterMate
  • "No layers available" message

Solutions:

  1. Force Reload Layers (F5): ⭐ NEW in v2.3.7

    • Press F5 while FilterMate dockwidget is focused
    • Wait for reload indicator ("⟳") to complete
    • All project layers will be reloaded
    • This is the fastest solution

  2. Reload plugin:

    • Plugins → Plugin Manager
    • Find FilterMate
    • Click "Reload Plugin"

  3. Close and reopen dockwidget:

    • Click FilterMate toolbar icon to close
    • Click again to reopen

  4. Restart QGIS (last resort):

    • Save your project first
    • Restart QGIS
    • Reopen project

Why This Happens:

  • QGIS signal timing can vary between systems
  • PostgreSQL layers may need extra initialization time
  • Project state cleanup may be incomplete

Technical Details: The F5 reload feature (v2.3.7) forces a complete state reset:

  • Clears all cached layer references
  • Cancels pending tasks
  • Resets all state flags
  • Reinitializes database connections
  • Reloads all vector layers from current project

Filtering Issues​

Filter Not Applied​

Symptoms:

  • Layer still shows all features
  • No visible change

Check:

  1. Expression syntax:

    # Correct
    population > 10000

    # Wrong
    population > 10,000  # No commas in numbers

  2. Field names:

    • Case-sensitive
    • Use quotes for special characters: "Field Name"

  3. Layer provider:

    • PostgreSQL: Server-side filtering
    • Others: QGIS expression engine

  4. Backend warnings:

    • Check message bar for warnings
    • May indicate performance issues

Geometric Filter Returns No Features​

Possible Causes:

  1. CRS mismatch:

    # Check CRS
    Source CRS: EPSG:4326 (WGS84)
    Target CRS: EPSG:3857 (Web Mercator)
    # FilterMate automatically reprojects

  2. Buffer too small/large:

    • Units in layer CRS
    • Check unit (meters vs degrees)

  3. Invalid geometries:

    • FilterMate attempts automatic repair
    • Check QGIS message bar

Solutions:

  1. Verify CRS:

    • Layer Properties → Information
    • Ensure both layers have valid CRS

  2. Test without buffer:

    • Set buffer to 0
    • Test predicate alone

  3. Repair geometries:

    • Vector → Geometry Tools → Fix Geometries

Expression Conversion Failed​

Error:

Cannot convert expression to backend SQL

Cause:

  • QGIS expression not supported by backend

Solutions:

  1. Use simpler expressions:

    # Instead of
    to_string($area) LIKE '1000%'

    # Use
    $area >= 1000 AND $area < 2000

  2. Check backend compatibility:

    • PostgreSQL: Full PostGIS functions
    • Spatialite: ~90% PostGIS compatible
    • OGR: Limited expressions

Performance Issues​

Filtering Very Slow​

Symptoms:

  • Operation takes > 30 seconds
  • UI freezes

Solutions:

  1. Check dataset size:

    layer.featureCount()
    # > 50,000: Consider PostgreSQL

  2. Use PostgreSQL backend:

    pip install psycopg2-binary
    • Convert data to PostGIS
    • 10-100× faster for large datasets

  3. Optimize expression:

    # Slow: Complex expression
    to_string($area) LIKE '%000'

    # Fast: Simple comparison
    $area > 1000

  4. Reduce buffer distance:

    • Smaller buffers = faster processing

  5. Filter in stages:

    • Apply attribute filter first
    • Then geometric filter

UI Not Responsive​

Cause:

  • Heavy operation running

Check:

  1. Task progress:

    • Look for progress bar in QGIS
    • Bottom-right corner

  2. Cancel if needed:

    • Click "X" on progress bar
    • Or wait for completion

Prevention:

  • Use PostgreSQL for large datasets
  • Test on subset first

Export Issues​

Export Failed​

Error:

Cannot write to output file

Causes:

  1. File permissions:

    # Check write permissions
    touch /path/to/output.gpkg

  2. File already open:

    • Close in QGIS
    • Close in external applications

  3. Disk space:

    df -h  # Check available space

  4. Invalid path:

    • Use absolute paths
    • Avoid special characters

Export Incomplete​

Symptoms:

  • Fewer features than expected
  • Missing attributes

Check:

  1. Active filter:

    • Export exports filtered features
    • Clear filter to export all

  2. Field selection:

    • Verify all fields selected
    • Check "Select All"

  3. CRS transformation:

    • Some features may be outside target CRS bounds

Styles Not Exported​

Check:

  1. Style export enabled:

    • Configuration → STYLES_TO_EXPORT
    • Set to "QML" or "SLD"

  2. Format supports styles:

    • GeoPackage: Yes
    • Shapefile: Yes (.qml/.sld file)
    • GeoJSON: No (no style support)

UI Issues​

Interface Too Large/Small​

Solution:

  1. Change UI profile:

    • Configuration tab
    • UI_PROFILE → "compact" or "normal"

  2. Auto mode:

    • Set to "auto"
    • Adapts to screen resolution

Theme Not Applied​

Check:

  1. Theme setting:

    • Configuration → ACTIVE_THEME
    • Options: auto, default, dark, light

  2. Theme source:

    • THEME_SOURCE → "qgis" to match QGIS

  3. Restart may be needed:

    • Close and reopen FilterMate panel

Configuration Changes Not Saved​

Check:

  1. Auto-save enabled (v2.2.2+):

    • Changes save automatically
    • No manual save needed

  2. File permissions:

    # Check config file writable
    ls -l config/config.json

  3. Valid JSON:

    • Syntax errors prevent saving
    • Check QGIS message bar

Geometry Issues​

Invalid Geometry Warning​

Message:

Invalid geometry detected. Attempting repair...

FilterMate Action:

  • Automatic repair with 5 strategies
  • Usually succeeds

If Fails:

  1. Manual repair:

    • Vector → Geometry Tools → Fix Geometries

  2. Check geometry:

    # In QGIS Python Console
    layer = iface.activeLayer()
    for f in layer.getFeatures():
        if not f.geometry().isGeosValid():
            print(f"Invalid: {f.id()}")

  3. Simplify geometry:

    • Vector → Geometry Tools → Simplify

Buffer Operation Failed​

Causes:

  1. Invalid source geometry

    • See "Invalid Geometry Warning" above

  2. Negative buffer:

    • Use positive values only

  3. Buffer too large:

    • May exceed system memory
    • Reduce buffer distance

Debug Mode​

Enable Debug Logging​

  1. Set in configuration:

    {
      "ENABLE_DEBUG_LOGGING": true
    }

  2. Restart FilterMate

  3. View logs:

    • QGIS Python Console
    • Or check log file (if configured)

Log Locations​

Linux:

~/.local/share/QGIS/QGIS3/profiles/default/python/plugins/filter_mate/logs/

Windows:

%APPDATA%\QGIS\QGIS3\profiles\default\python\plugins\filter_mate\logs\

macOS:

~/Library/Application Support/QGIS/QGIS3/profiles/default/python/plugins/filter_mate/logs/

Getting Help​

Before Reporting Issues​

  1. Check this guide
  2. Enable debug logging
  3. Try with test data
  4. Check QGIS version compatibility

Reporting Issues​

Include:

  1. FilterMate version
  2. QGIS version
  3. Operating system
  4. Backend type (PostgreSQL/Spatialite/OGR)
  5. Error message (from QGIS console)
  6. Steps to reproduce
  7. Debug logs (if enabled)

Where to Get Help​

Further Reading​