Function createQuerySignalFn

packages/core/src/render3/queries/query_reactive.ts:43–79

* A signal factory function in charge of creating a new computed signal capturing query * results. This centralized creation function is used by all types of queries (child / children, * required / optional). * * @param firstOnly indicates if all or only the first result should be returned * @p

(
  firstOnly: boolean,
  required: boolean,
  opts?: {debugName?: string},
)

 * @returns a read-only signal with query results
 */
function createQuerySignalFn<V>(
  firstOnly: boolean,
  required: boolean,
  opts?: {debugName?: string},
) {
  let node: QuerySignalNode<V>;
  const signalFn = createComputed(() => {
    // A dedicated signal that increments its value every time a query changes its dirty status. By
    // using this signal we can implement a query as computed and avoid creation of a specialized
    // reactive node type. Please note that a query gets marked dirty under the following
    // circumstances:
    // - a view (where a query is active) finished its first creation pass;
    // - a new view is inserted / deleted and it impacts query results.
    node._dirtyCounter();

    const value = refreshSignalQuery<V>(node, firstOnly);

    if (required && value === undefined) {
      throw new RuntimeError(
        RuntimeErrorCode.REQUIRED_QUERY_NO_VALUE,
        ngDevMode && 'Child query result is required but no value is available.',
      );
    }

    return value;
  });
  node = signalFn[SIGNAL] as QuerySignalNode<V>;
  node._dirtyCounter = signal(0);
  node._flatValue = undefined;

  if (ngDevMode) {
    signalFn.toString = () => `[Query Signal]`;
    node.debugName = opts?.debugName;
  }

  return signalFn;
}

export function createSingleResultOptionalQuerySignalFn<ReadT>(opts?: {
  debugName?: string;