Repo.count in Ecto
I have often wanted to just do the following but Ecto’s Repo module doesn’t have a count method.
iex> MyApp.Repo.count(MyApp.Account) 42
It is not too difficult to create a
count function that will allow you to count the results of any query.
defmodule MyApp.DBUtils do import Ecto.Query, only: [from: 2] @doc "Generate a select count(id) on any query" def count(query), do: from t in clean_query_for_count(query), select: count(t.id) # Remove the select field from the query if it exists defp clean_query_for_count(query), do: Ecto.Query.exclude(query, :select) end
This will provide a shortcut for counting any query
MyApp.DBUtils.count(MyApp.Account) |> Repo.one!
Now, to enable
Repo.count we can modify the repo module usually found in
defmodule MyApp.Repo do use Ecto.Repo, otp_app: :my_app def count(query), do: MyApp.DBUtils.count(query) |> __MODULE__.one! end
That’s it. This will enable a count on any query including complicated queries and those that have a select expression set.