code: public final ListFieldsPagedResponse listFields(String parent) {
      ListFieldsRequest request = ListFieldsRequest.newBuilder().setParent(parent).build();
      return listFields(request);
    }
docs: Lists the field configuration and metadata for this database.
  
  <p>Currently, [FirestoreAdmin.ListFields][google.firestore.admin.v1.FirestoreAdmin.ListFields]
  only supports listing fields that have been explicitly overridden. To issue this query, call
  [FirestoreAdmin.ListFields][google.firestore.admin.v1.FirestoreAdmin.ListFields] with the
  filter set to `indexConfig.usesAncestorConfig:false`.
  
  <p>Sample code:
  
  <pre><code>
  try (FirestoreAdminClient firestoreAdminClient = FirestoreAdminClient.create()) {
  ParentName parent = ParentName.of("[PROJECT]", "[DATABASE]", "[COLLECTION_ID]");
  for (Field element : firestoreAdminClient.listFields(parent.toString()).iterateAll()) {
  // doThingsWith(element);
  }
  }
  </code></pre>
  
  @param parent A parent name of the form
  `projects/{project_id}/databases/{database_id}/collectionGroups/{collection_id}`
  @throws com.google.api.gax.rpc.ApiException if the remote call fails