octobercms/october · error · ApplicationException

Model ':class' does not contain a definition for…

Error message

Model ':class' does not contain a definition for ':relation'.

What it means

Thrown by resolveModelAttribute when the underlying form field's model resolution fails — the model class bound to the form widget has no relation (or nested attribute path) definition matching the requested name. It wraps the low-level exception into an ApplicationException with a localized message naming the class and relation. Consumers are getRelationModel, getRelationObject, getRelationType and isRelationTypeSingular, so any widget using them (e.g. record finder, relation manager) triggers this when its valueFrom/fieldName references an undefined relation.

Solutions

1. Add the missing relation method (e.g. public function myRelation()) to the model class named in the message
2. Correct the field name / valueFrom configuration in the form field YAML so it points to a relation that actually exists on the model
3. If targeting a nested attribute, verify each segment of the dotted path resolves on the corresponding model

When it happens

Trigger: Thrown at modules/backend/traits/FormModelWidget.php:30 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of octobercms/october@b608633a7e (2026-08-21). Data as JSON: /api/errors/13c1d6d72113951f. Report an issue: GitHub.

Appendix: source

Thrown at modules/backend/traits/FormModelWidget.php:30

 * @package october\backend
 * @author Alexey Bobkov, Samuel Georges
 */
trait FormModelWidget
{
    /**
     * Returns the final model and attribute name of
     * a nested HTML array attribute.
     * Eg: [$model, $attribute] = $this->resolveModelAttribute($this->valueFrom);
     * @param  string $attribute.
     * @return array
     */
    public function resolveModelAttribute($attribute)
    {
        try {
            return $this->formField->resolveModelAttribute($this->model, $attribute);
        }
        catch (Exception $ex) {
            throw new ApplicationException(Lang::get('backend::lang.model.missing_relation', [
                'class' => get_class($this->model),
                'relation' => $attribute
            ]));
        }
    }

    /**
     * nearestModelAttribute
     */
    public function nearestModelAttribute($attribute)
    {
        return $this->formField->nearestModelAttribute($this->model, $attribute);
    }

    /**
     * Returns the model of a relation type,
     * supports nesting via HTML array.
     * @return Relation

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