Filter on associations?

[Kevin Brown]

From the documentation, it's difficult to tell how to filter/query on associated records. Is that part of the feature set? If so, I'll be happy to provide some documentation/contribution.

[Christian Di Lorenzo]

Yes, it is. It's just because of how the underlying database works with primary/foreign keys. See this issue: #38. I would be supremely grateful for a contribution.

[Kevin Brown]

As I understand this issue, this will require multiple db calls?
I think a quick example of a has_one relationship filter/query would be most beneficial. 😃

[Christian Di Lorenzo]

Perhaps I did not understand you correctly. Are you wanting to filter on a joined table from a given query? In that case, you'll need to base the filter off of that association (or reference it potentially by the relationship key path). I'm happy to consider a particular use case. That might clarify the issue a bit.

[Kevin Brown]

Let's say I have a user & users have_one :profile.

I want to query various things on the profile as well as the "base query" user table.
The user may have an email and various fields, while the profile contains first/last name and various other fields.
I have a bit of a better idea now, which I'll keep working at in my free time this next week. 😸

[Kevin Brown]

As a non-working example:

  def filter_config(:users) do
    defconfig do
      text :email
      number :status
      ...
    end
  end

  def pi_filter(:profile) do
    defconfig do
      text :first_name
      ...
    end
  end

{:ok, filter} <- Filtrex.parse_params(filter_config(:users), params["user"] || %{}),
{:ok, profile_filter} <- Filtrex.parse_params(pi_filter(:profile), params["profile"] || %{}),
result <- do_query(filter, profile_filter) do ..

  defp do_query(filter, profile_filter, params) do
    User
    |> preload([:profile, ...])
    |> profile_query(profile_filter)
    |> Filtrex.query(filter)
    |> order_by(^sort(params))
    |> paginate(Repo, params, @pagination)
  end

  def profile_query(query, profile_filter) do
    Profile |> Filtrex.query(profile_filter)
  end

Obviously this doesn't work, but I imagine some composition should work.

[Kevin Brown]

@rcdilorenzo Got it working--let me know your thoughts and I'll provide a readme update showing usage of filtering on associations.

defmodule MyApp.Users.Users do
  import Ecto.Query, warn: false
  import Filtrex.Type.Config

  alias MyApp.Repo
  alias MyApp.Users.{User, PersonalInformation}

  def filter_users(params \\ %{}) do
    with {:ok, filter} <- Filtrex.parse_params(filter_config(:users), params["user"] || %{}),
         {:ok, pi_filter} <- Filtrex.parse_params(pi_filter(:pi), params["pi"] || %{}),
         users <- do_filter_users(filter, pi_filter, params) do
      {:ok, %{users: users}}
    else
      {:error, error} -> {:error, error}
      error -> {:error, error}
    end
  end

  defp do_filter_users(filter, pi_filter, params) do
    q1 = User
    |> Filtrex.query(filter)

    q2 = PersonalInformation
    |> Filtrex.query(pi_filter)


    qx =
      from user in q1,
      join: pi in ^q2,
      on: pi.user_id == user.id
    qx
    |> preload([:personal_information, :market])
    |> order_by(^sort(params))
    |> Repo.filter(params)
  end

  def filter_config(:users) do
    defconfig do
      text :email
      number :status
      ...
    end
  end

  def pi_filter(:pi) do
    defconfig do
      text :first_name
    end
  end
end

[Kevin Brown]

I imagine Ecto 3 will vastly improve this and allow for dynamic building...but until then, I think this is the only way to accomplish what I'm looking for.

[Christian Di Lorenzo]

Excellent! This looks good. If it's possible to simplify parts, I think that would be even better. For example, the following lines could probably be excluded and yet still convey how association filtering can be accomplished:

  # ...
  else
      {:error, error} -> {:error, error}
      error -> {:error, error}
  # ...

[Kevin Brown]

Yeah, I probably won't include that part b/c those tuples are used on my controllers. 😸

I'll send you a PR! (hopefully sooner than later)