I have a Content Type with a field that references 6 different paragraph types. The field is set up to accept unlimited values. For one of the types I would like to have exactly four values added. I've been trying to add a Constraint but it seems that Constraints are built to check if a fields values are valid and not if there are only four items
Is using hook_entity_bundle_field_info_alter the correct hook or should I be focused on using hook_entity_type_alter or maybe even some other method?
Yes, use hook_entity_bundle_field_info_alter and when you add a constraint to the field (and not to a item or property), your constraint gets the entire field item list, so you can check how many items you have of which type, see FieldConfigInterface::addConstraint:
function mymodule_entity_bundle_field_info_alter(&$fields, \Drupal\Core\Entity\EntityTypeInterface $entity_type, $bundle) { if ($entity_type->id() == 'node' && $bundle == 'page') { $fields['field_paragraph']->addConstraint('MymoduleParagraphTypes'); } } Example for a constraint restricting the field to four paragraph items of a specific type:
public function validate($items, Constraint $constraint) { $paragraphs = array_filter($items->referencedEntities(), function ($paragraph) { return $paragraph->bundle() === 'image'; }); if (!empty($paragraphs) && count($paragraphs) != 4) { $this->context->addViolation($constraint->errorMessage); } } You can generate the constraint with the Drush command:
drush generate plugin-constraint Edit: If you need to check field values inside of the paragraphs then use $item->entity. See How to validate a paragraph field?
MymoduleParagraphTypes, which you find in the first class generated. Then put the example code in the second class.