loadExists method

Future<OrmMigrationRecord> loadExists(String relation, { String? alias, PredicateCallback<OrmEntity>? constraint, })

Lazily loads the existence of a relation.

Stores the boolean result as an attribute with the suffix _exists.

Example:

await post.loadExists('comments');
if (post.getAttribute<bool>('comments_exists') == true) {
  print('Post has comments');
}

Implementation

Future<TModel> loadExists(
  String relation, {
  String? alias,
  PredicateCallback<OrmEntity>? constraint,
}) async {
  if (ModelRelations.preventsLazyLoading) {
    throw LazyLoadingViolationException(runtimeType, relation);
  }

  final def = expectDefinition();
  final resolver = _resolveResolverFor(def);
  final context = _requireQueryContext(resolver);

  // Find the relation definition
  final relationDef = def.relations.cast<RelationDefinition?>().firstWhere(
    (r) => r?.name == relation,
    orElse: () => null,
  );

  if (relationDef == null) {
    throw ArgumentError('Relation "$relation" not found on ${def.modelName}');
  }

  final existsAlias = alias ?? '${relation}_exists';

  // Build a query for this model with withExists
  final query = context.queryFromDefinition(def);

  // Get the primary key value
  final pkField = def.primaryKeyField;
  if (pkField == null) {
    throw StateError('Cannot load exists on model without primary key');
  }

  final pkValue = _asAttributes.getAttribute(pkField.columnName);
  if (pkValue == null) {
    throw StateError('Cannot load exists on model without primary key value');
  }

  // Query for this specific model with exists
  final queryWithAggregate = query
      .where(pkField.columnName, pkValue)
      .withExists(relation, alias: existsAlias, constraint: constraint);

  final rows = await queryWithAggregate.get();
  if (rows.isNotEmpty) {
    final result = rows.first;
    // SQL returns 1/0 for EXISTS, convert to boolean
    final value = result._asAttributes.getAttribute(existsAlias);
    final exists = value == true || value == 1;
    _asAttributes.setAttribute(existsAlias, exists);
  }

  return _self();
}