Query Collection from Specific Document Id Tied To A UserId in Firebase.

Hi there,

I'm building a chat interface and I'm having trouble retrieving the messages which are stored in firebase. I want to retrieve collection "messages" from a specific {chatId} and {userId}. I had no problem retrieving all the messages with a database query when had all the messages stored under "Chats" and only had to refer to the {userId}, but now that I've added another level with multiple chatIds, each with their own collection of messages, I can't seem to retrieve the messages. When I use the database query, the parent ref is the {userId}, but I don't know how to specify which {chatId} I want to retrieve. All the messages are then displayed in a list view, with the "sender" field determining how it gets displayed.

Below is my firestore database structure.

users (Collection)

└── {userId} (Document)

├── Chats (Sub Collection)

│ └── {chatId} (Document)

│ ├── title (Field - String)

│ ├── createdAt (Field - Date)

│ └── lastMessageAt (Field - Date)

│ └── messages (Sub Collection)

│ └── {messageId} (Document)

│ ├── msg (field - string)

│ ├── sender (field - string)

│ ├── timestamp (field - date)

│ ├── bookmark (field - boolean)

Any help is greatly appreciated.