anchor.diff:    }
   
     void getDataOnce_customObjects() {
  -    // [START get_data_once_custom_objects]
       // TODO: should this be included?
       // This isn't really specific to Firestore, it's just serdes
  +    // [START get_data_once_custom_objects]
       final docRef = db.collection("cities").doc("BJ");
       docRef.get().then((documentSnapshot) {
         final data = documentSnapshot.data() as Map<String, dynamic>;
  
positive.code: 
    void transactions_batchedWrites() {
      // [START transactions_batched_writes]
      /*
  
  
  
  
  
  
  // Commit the batch
  batch.commit().then(() => {
      // ...
  });
     */
      // Get a new write batch
      final batch = db.batch();
  
  
negative.code: 
    void performSimpleAndCompoundQueries_queryOperators() {
      // [START perform_simple_and_compound_queries_query_operators]
      final citiesRef = db.collection("cities");
      final stateQuery = citiesRef.where("state", isEqualTo: "CA");
      final populationQuery = citiesRef.where("population", isLessThan: 100000);
  