What causes "Missing source for '{$this->fieldName}'." in octobercms/october?

Add `source: ` directly under the entries field config.

octobercms/october · error · SystemException

Missing source for '{$this->fieldName}'.

Error message

Missing source for '{$this->fieldName}'.

What it means

getSourceBlueprint() lazily resolves an entries field's `source` to a section blueprint via the BlueprintIndexer; the first guard rejects a falsy source with SystemException("Missing source for '{field}'."). Entries fields store relations to other blueprints, so without a source there is nothing to relate to.

Source

Thrown at modules/tailor/contentfields/EntriesField.php:350

                    ? array_merge($fieldConfig[$transfer], (array) $this->controller[$transfer])
                    : $this->controller[$transfer];
            }
        }

        $field->controller($fieldConfig);
    }

    /**
     * getSourceBlueprint validates and converts source to a blueprint
     */
    protected function getSourceBlueprint()
    {
        if ($this->sourceCache !== null) {
            return $this->sourceCache;
        }

        if (!$this->source) {
            throw new SystemException("Missing source for '{$this->fieldName}'.");
        }

        $indexer = BlueprintIndexer::instance();

        $uuid = $indexer->hasSection($this->source);
        if (!$uuid) {
            throw new SystemException("Invalid source '{$this->source}' for '{$this->fieldName}'.");
        }

        return $this->sourceCache = BlueprintIndexer::instance()->findSection($uuid);
    }

    /**
     * getSourceFieldset returns the source fieldset definition for checking inverse relations
     */
    protected function getSourceFieldset()
    {
        if ($this->fieldsetCache !== null) {

View on GitHub (pinned to b608633a7e)

Solutions

Add `source: <blueprint-handle-or-uuid>` directly under the entries field config.
Check YAML indentation — `source` must be a direct child key of the field.
If the field shouldn't be relational, switch the type to text or another non-relational field.

Example fix

# before
fields:
  related_posts:
    label: Related Posts
    type: entries

# after
fields:
  related_posts:
    label: Related Posts
    type: entries
    source: blog/posts

Defensive patterns

Strategy: validation

Validate before calling

$fieldConfig = $blueprintContent['fields'][$fieldName] ?? [];
if (($fieldConfig['type'] ?? '') === 'entries' && empty($fieldConfig['source'])) {
    throw new InvalidArgumentException("Field '{$fieldName}' of type entries requires a source.");
}

Type guard

function hasRequiredSource(array $fieldConfig): bool
{
    return !empty($fieldConfig['source']);
}

Try / catch

try {
    // tailor:refresh / record save
} catch (\SystemException $e) {
    // message names the field; add source: <handle> to its YAML config
}

Prevention

When authoring entries fields, always include source (and check indentation) in the same edit.
Use a fieldset template/snippet that includes source for relational fields.

When it happens

Trigger: A field with `type: entries` (or `type: entry`) is defined without a `source:` key in the blueprint or imported fieldset. The exception fires whenever Tailor extends models or builds the schema for a record using that fieldset.

Common situations: Field config copied from a recordfinder or incomplete example; YAML indentation placing `source` under another key so it parses as null; shared fieldsets where source is expected per-blueprint but omitted.

Related errors

AI-assisted analysis of octobercms/october@b608633a7e (2026-08-21). Data as JSON: /api/errors/8f0040294e2e2595. Report an issue: GitHub.