Firestore: How to query data from a map of an array

Question

Here is the schema for test db:

I want to write a query that can get all the documents where contacts have id=1 in any of the array index.

I have checked array_contains operator for firestore but the thing is my array have map which then have field id.

Thanks

Answer 1

You currently can't build a query that looks for an object field within an array. The only things you can find in an array are the entire contents of an array element, not a part of an element.

With NoSQL type databases, the usual practice is to structure you data in a way that suits your queries. So, in your case, you're going to have to structure you data to let you find documents where an array item contains a certain string. So, you could create another array that contains just the strings you want to query for. You will have make sure to keep these arrays up to date.

You could also reconsider the use of an array here. Arrays are good for positional data, but unless these contacts need to be stored in a certain order, you might want to instead store an object whose keys are the id, and whose field data also contains the id and name.

Answer 2

As Doug said, you can't query it, but, if you could structure your data to something that looks like this

1. Store your data as a map
2. Use id as key and name as value
3. Now you can write a query that can get all the documents where contacts have id=1

db.collection("test").where("contacts.1", ">=", "").get()

Answer 3

If you have an array of maps or objects and want to get the docoments that contains this specific map/object like this ? array_of_maps.png

you can use

queryForCategory(categName: string, categAlias: string): Observable[] {
    firestore.collection('<Collection name>', ref =>

        ref.where('categories',
          "array-contains", {
            "alias": categAlias,
            "title": categName
          }

Answer 4

One soulions is as @Doug said, to add array with the data you need to query, and keep it uptodate.

Another solution is to make contacts as sub collection of the document, an then you could make queries of the contacts and get its parrent.

final Query contacts = db.collectionGroup("contacts").whereEqualTo("id", 1);
for (DocumentSnapshot document : querySnapshot.get().getDocuments()) {
  System.out.println(document.getId());
  System.out.println(document.getString("parent_id"));
}

If you don't want to add parent as another field, you can get it from parent reference, check this answer https://stackoverflow.com/a/56223319/1278463

snapshot.getRef().getParent().getParent().collection("people")

https://firebase.google.com/docs/firestore/query-data/queries#collection-group-query