2 回答
You should validate the keys in the entries map first.
ids = Map.keys(entries)
true = Enum.all?(ids, &is_integer/1)
Ecto will convert strings to integers when interpolating into a query:
iex(40)> Ecto.Query.from(u in Users, where: u.id in ^[1, 2, "3", nil], select: u.id) |> Repo.all()
outputs the following debug log:
[debug] QUERY OK source="users" db=0.8ms
SELECT u0."id" FROM "users" AS r0 WHERE (r0."id" = ANY($1)) [[1, 2, 3, nil]]
Notice it coerced the string "3" to an integer and allowed the nil.
However a map will not be so kind:
iex(42)> users = %{1 => %{name: "joe"}, 2 => %{name: "jill"}}
%{1 => %{name: "joe"}, 2 => %{name: "jill"}}
iex(43)> users["1"]
nil
So in the code where you are using the keys from entries for database lookups and map lookups, it could be producing different results.
I've already figured out that the problem has very little to do with my fetch/2 function itself, rather, it had to do with my implementation of the presence module and channel in this case. Basically, the fetch/2 function was being called 4 times every time some one entered the chat room and two out of the four times it was being called with an empty list value [].
Obviously, you can't query a Ecto model with an empty list so it was throwing an error in that case as well. I tried putting guards on the fetch function to filter out the empty list calls but it would not show me the metas map data that I was looking for even when the query succeeded.
Also, the other main problem was my implementation or lack of implementation of a token. I wouldn't have to pass around the user model data through fetch function metas map if I was using a token for joining the chat room rather then just a user (aka the just a username). After making that realization, I was able to successfully connect the user model data with the channel and show it through the JS layer and ultimately, put it on the client.
Anyways guys, thanks for the suggestions. You may not have answered the question (It was my fault for asking the wrong question), but you certainly helped me get there. And also gave me the tools to form a much better understanding of the framework in general on the way.
If/When I have any more questions, I will make sure that I am asking the correct questions before posting them to stack overflow, that way I wont be wasting time.