How do I add an array of custom objects to a Firestore document field?

Question

I want to update or create a field called "tags" inside a document, which should contain an array of custom objects called Tags ("tag_name", "tag_color"). To update or create such a field, I must pass an array of said object (not able to pass single objects, since it would be ineffective and expensive). How can I achieve this? I have tried adding an ArrayList of Tag objects to a Hashmap:

HashMap<String, ArrayList<GenericTagModel>> myObject = new HashMap<>();
                ArrayList<GenericTagModel> toArrayList = new ArrayList<GenericTagModel>(usedModels);
                myObject.put("tags",toArrayList);
                db.collection("users").document(user.getUid()).set(myObject, SetOptions.merge());

But all this does is add a field with nothing inside of it: "tags:[]"

What can I do?

Answer 1

You are getting tags:[] because your toArrayList empty, does not contain any GenericTagModel objects. To solve this, please use the following lines of code:

HashMap<String, ArrayList<GenericTagModel>> myObject = new HashMap<>();
ArrayList<GenericTagModel> toArrayList = new ArrayList<GenericTagModel>(usedModels);
toArrayList.add(new GenericTagModel("redTag", "Red")); //Populate ArrayList
toArrayList.add(new GenericTagModel("blueTag", "Blue")); //Populate ArrayList
toArrayList.add(new GenericTagModel("greenTag", "Green")); //Populate ArrayList
myObject.put("tags",toArrayList);
db.collection("users").document(user.getUid()).set(myObject, SetOptions.merge());

The result will be an array that will contain theree GenericTagModel objects.