flutter firestore, add new object in array

@anmol.majhail 's is right, but to solve @Sami Ullah's problem, you must first make a list and add the object into the list like this:

var list = [objectBeingAdded];
Firestore.instance.collection('city').document('Attractions').updateData({"data": FieldValue.arrayUnion(list)});

Null safe code:

Say this is the data you want to add

Map<String, dynamic> someData = {
  'foo': 1,
  'bar': true,
};

• Add the data with unique auto-generated ID:

  var collection = FirebaseFirestore.instance.collection('collection');
  collection 
      .add(someData) 
      .then((_) => print('Added'))
      .catchError((error) => print('Add failed: $error'));
  

• Add the data with your own ID:

  var collection = FirebaseFirestore.instance.collection('collection');
  collection 
      .doc('document_id') // <-- Document ID
      .set(someData) 
      .then((_) => print('Added'))
      .catchError((error) => print('Add failed: $error'));
  

• Add the object to an array:

  var collection = FirebaseFirestore.instance.collection('collection');
  collection 
      .doc('document_id') // <-- Document ID
      .set({'data': FieldValue.arrayUnion(list)}) // <-- Add data
      .then((_) => print('Added'))
      .catchError((error) => print('Add failed: $error'));
  

2023 Updated Syntax:

From the Fireabse docs

final washingtonRef = db.collection("cities").doc("DC");

// Atomically add a new region to the "regions" array field.
washingtonRef.update({
  "regions": FieldValue.arrayUnion(["greater_virginia"]),
});

// Atomically remove a region from the "regions" array field.
washingtonRef.update({
  "regions": FieldValue.arrayRemove(["east_coast"]),
});

This is a working function I built that adds new Maps to an array in my Firestore Services class. I'm using Json Serializable to annotate all my model classes. userTemplateSections is a data field in my userTemplate firestore documents. I take userTemplate as a constructor of the 'addUserTemplateSection' function to make sure I'm editing the correct document.

I also added the function I made to delete Maps from a firestore document array.

'''

Future<void> addUserTemplateSection(
      {UserTemplate userTemplate, String title, String summary}) async {
    try {
      final UserTemplateSection userTemplateSection =
          UserTemplateSection(title: title, summary: summary);
      await _firestore
          .document(FirestorePath.userTemplate(uid, userTemplate.id))
          .updateData(
        {
          'userTemplateSections':
              FieldValue.arrayUnion([userTemplateSection.toJson()])
        },
      );
    } catch (e) {
      print(e);
    }
  }

'''

'''

Future<void> deleteUserTemplateSection({
    UserTemplate userTemplate,
    UserTemplateSection userTemplateSection,
  }) async {
    try {
      await _firestore
          .document(FirestorePath.userTemplate(uid, userTemplate.id))
          .updateData(
        {
          'userTemplateSections':
              FieldValue.arrayRemove([userTemplateSection.toJson()])
        },
      );
    } catch (e) {
      print(e);
    }
  }

'''