如何在 Xamarin Android 中将 sql 查询应用于 Firebase？

Question

I need get return data from Firebase. In Sql query it would be like this:

Select * from * Group By field1, field2 HAVING count(*)=1

How to apply above to FireBase in Xamarin Android. So I have node "chats", here I want retrieve record only not repeated on field "user_email":

chats
 |-...
   |---date_and_time:
   |---user_email:
 |-...
   |---date_and_time:
   |---user_email:
 ... 

at this moment I get whole data from "chat", here code:

public List<MessageContent> listOfContacts = new List<MessageContent>();
FirebaseClient firebase;
...
firebase = new FirebaseClient(GetString(Resource.String.database_name));
...
var firebaseContacts = await firebase.Child("chats")
                                                 .OnceAsync<MessageContent>();
            foreach (var item in firebaseContacts)
                listOfContacts.Add(item.Object);  

Answer 1

Firebase's realtime database is a NoSQL database. Trying to directly map a SQL query to it is going to give you a rough time. I highly recommend reading NoSQL data modeling and watching Firebase for SQL developers .

In NoSQL databases you typically get more complex write operations and in return get more performant/scalable read operations. So in your case, that could mean that you actually store a list of the records that you're trying to query and update that list with every write.

Some previous questions that deal with similar scenarios can be found in this list .