Why Are My Attribute Constraints Not Respected in QField?

For a Super User of QField, the transition from a desktop QGIS environment to a mobile field workflow is usually seamless. However, one of the most common technical hurdles is finding that attribute constraints—such as "Not Null," unique values, or custom expressions—are seemingly ignored during data entry. When a constraint is "not respected," it compromises the integrity of your GIS database and leads to significant cleanup work for the webmaster.

Here is the technical diagnostic path to resolving constraint failures in your mobile web application workflow.

1. The "Enforce Constraint" Toggle

In QGIS, there is a critical distinction between a "Constraint" and an "Enforced Constraint." By default, QGIS often treats constraints as warnings.

• The Fix: In your Layer Properties under Attributes Form, you must check the "Enforce expression constraint" box. If this is not checked, QField may allow the user to save the feature despite the validation failing.
• Client-Side Validation: QField performs validation at the moment of "pushing" the checkmark to save. If the enforcement is not set to "Hard," the mobile web application will prioritize saving the geometry over the attribute rules.

2. Unsupported Expression Functions

QField uses a mobile-optimized version of the QGIS expression engine. Some complex functions that work perfectly in a desktop VPS environment may not be supported or may behave differently on Android/iOS.

• Aggregate Functions: Functions like aggregate() or relation_aggregate() can be extremely slow or fail to trigger in QField if the project is not optimized.
• Geometry Relations: Expressions relying on get_feature() or spatial joins (e.g., within()) require the referenced layers to be available offline and correctly indexed. If the "Background Layer" is missing, the constraint logic breaks.

3. The QFieldSync Plugin Bottleneck

Often, the issue isn't the constraint itself, but how the project was packaged. When using the QFieldSync plugin, certain "Widget" settings can be stripped or modified to fit the mobile schema.

1. Check the "Cloud" or "Package" settings in QFieldSync.
2. Ensure that the "Action" for the layer is set to "Offline Editing" and not "Read Only."
3. Verify that the .qgs or .qgz file within the exported package actually contains the <constraints> tags in the XML structure.

4. Evaluation Trigger: "On Change" vs. "On Save"

Constraints in QField are typically evaluated when a field loses focus or when the feature is saved. If your SEO-driven data collection requires real-time feedback, you must ensure that your UI settings in QGIS are compatible.

• If a constraint relies on a "Default Value," ensure "Apply default value on update" is checked if you want the constraint to re-evaluate when the feature is edited later.

5. Data Integrity and SEO Impact

From a webmaster perspective, clean data is essential for SEO maps and local Google Search results. If your QField users are uploading points with missing "Business Name" or "Address" fields because constraints weren't respected:

• Schema Validation: Your web application might fail to generate the correct JSON-LD structured data.
• User Trust: Inaccurate map data leads to high bounce rates, which is a negative signal for Google Search rankings.
• E-E-A-T: Maintaining strict constraints demonstrates Expertise and Authoritativeness in your spatial data management.

Conclusion

If your constraints are not being respected in QField, the culprit is usually a missing "Enforce" checkbox in QGIS or a broken relationship in the offline package. By standardizing your attribute forms and testing expressions on the mobile device before a full field deployment, Super Users can ensure high-quality GIS data. Reliable field collection is the first step in creating a search engine optimized map that provides real value to users and search crawlers alike.