How write the query "user value is 4 and sort by time" in firebase database

Question

Why the compiler get an error for the "where" in below code?

query=dblink.orderByChild("time").where("user","==","4").LimitToLast(2);

how to write?

I want in query of runtime database

user value is 4 and sort by time

Answer 1

It seems you're using Firebase Realtime Database, but that doesn't have a where method. It can also order on at most one property, and then only filter on that property.

So if you want to filter on user, you'd do:

dblink.orderByChild("user").equalTo("4")

And if you want the latest two items, that'd be:

dblink.orderByChild("time").limitToLast(2)

But you can't combine those in a single query (keep reading for more).

For more on this, see the Firebase documentation on ordering and filtering data from the Realtime Database.

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One workaround that you might be able to use here is to combine the user and time values into a single property that allows the query: "user_time": "4_1698703155601".

With that property in place, you can then get the latest 2 nodes for user "4" with:

dblink.orderByChild("user_time").endAt("4_9999999999999").limitToLast(2)

So that "4_9999999999999" is the user ID and the highest possible timestamp value, and you then get the last two items that are before that time.

For more on this and other examples, see my answer to: Query based on multiple where clauses in Firebase