How to get an array from Firestore?

There are two solutions for your problem, one, you can cast the value from your document in the next way:

DocumentSnapshot document = task.getResult();
List<String> dungeonGroup = (List<String>) document.get("dungeon_group");

Or, and I would recommend you this solution because there is always a possibility that your model will change when you are developing your app . This solution is just model everything in Firebase POJO's even if they have just one parameter:

public class Dungeon {

    @PropertyName("dungeon_group")
    private List<String> dungeonGroup;

    public Dungeon() {
        // Must have a public no-argument constructor
    }

    // Initialize all fields of a dungeon
    public Dungeon(List<String> dungeonGroup) {
        this.dungeonGroup = dungeonGroup;
    }

    @PropertyName("dungeon_group")
    public List<String> getDungeonGroup() {
        return dungeonGroup;
    }

    @PropertyName("dungeon_group")
    public void setDungeonGroup(List<String> dungeonGroup) {
        this.dungeonGroup = dungeonGroup;
    }
}

Remember that you can use the Annotation @PropertyName to avoid call your variables in the same way that your value in the database. Doing it in this way finally you can just do:

DocumentSnapshot document = task.getResult();
Dungeon dungeon= toObject(Dungeon.class);

Hope that it will help you! Happy coding!

If you want to get the entire dungeon_group array you need to iterate over a Map like this:

Map<String, Object> map = documentSnapshot.getData();
for (Map.Entry<String, Object> entry : map.entrySet()) {
    if (entry.getKey().equals("dungeon_group")) {
        Log.d("TAG", entry.getValue().toString());
    }
}

But note, even if the dungeon_group object is stored in the database as an array, entry.getValue() returns an ArrayList and not an array.

A better approach for you would be if you consider this alternative database structure, in which each group is the key in a Map and all values are set to the boolean true:

dungeon_group: {
    3P: true,
    Urgent: true,
    Mission Chalange: true
    //and so on
}

Using this structure you'll also be able to query it based on the property that exists within the dungeon_group map, otherwise as in the official documentation:

Although Cloud Firestore can store arrays, it does not support querying array members or updating single array elements.

Edit 13 Jan 2021:

If instead of an array of String values you would have had an array of objects, then you can map that array of objects to a List of custom objects, as explained in the following article:

• How to map an array of objects from Cloud Firestore to a List of objects?

Edit 13 Aug 2018:

According to the updated documentation regarding array membership, now it is possible to filter data based on array values using whereArrayContains() method. A simple example would be:

CollectionReference citiesRef = db.collection("cities");
citiesRef.whereArrayContains("regions", "west_coast");

This query returns every city document where the regions field is an array that contains west_coast. If the array has multiple instances of the value you query on, the document is included in the results only once.

When you call DocumentSnapshot.getData(), it returns a Map. You're just calling toString() on that map, which is going to give you a dump of all the data in the document, and that's not particularly helpful. You need to access the dungeon_group field by name:

DocumentSnapshot document = task.getResult();
List<String> group = (List<String>) document.get("dungeon_group");

• edit: syntax error in typecasting