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Ash Elixir•2y ago

Building an aggregates-only Resource

I'm building an admin dashboard that will display several aggregate data points sourced from different database tables. These data points should be available from a single AshGraphql query. How would you do this? I created a resource called Dashboard. My first approach was to create a calculation to calculate a data point. That wasn't going anywhere, so I defined an primary read action that loaded the data point from inside the prepare block. That's where I'm at so far. The problem is that calling read() on the API returns nil. Here is an example of the kind of data I want to expose: - Member counts - Signup counts - Event counts - Attendee counts

54 Replies

moxleyOP•2y ago

The test for this looks like this:

test "success", ctx do
  ctx =
    ctx
    |> create_event()
    |> create_member(roles: ["admin"])
    |> create_signup()

  dashboard =
    Dashboard
    |> Ash.Query.set_tenant(ctx.org.id)
    |> Ash.Query.for_read(:read, %{}, actor: ctx.member)
    |> GF.Ash.read_one!(actor: ctx.member)

  # fails
  assert dashboard != nil
end

test "success", ctx do
  ctx =
    ctx
    |> create_event()
    |> create_member(roles: ["admin"])
    |> create_signup()

  dashboard =
    Dashboard
    |> Ash.Query.set_tenant(ctx.org.id)
    |> Ash.Query.for_read(:read, %{}, actor: ctx.member)
    |> GF.Ash.read_one!(actor: ctx.member)

  # fails
  assert dashboard != nil
end

The big challenge is trying to figure out what goes inside the MemberCountCalculation module. I'm not finding what I need in the documentation. And here's the action:

actions do
  read :read do
    get? true
    primary? true

    prepare fn query, context ->
      if context.actor do
        org_id = context.actor.org_id
        counts = GF.Members.basic_member_counts(org_id)

        Ash.DataLayer.Simple.set_data(query, [
          struct!(__MODULE__, %{
            members_count: counts.active_members
          })
        ])
      else
        query
      end
    end
  end
end

actions do
  read :read do
    get? true
    primary? true

    prepare fn query, context ->
      if context.actor do
        org_id = context.actor.org_id
        counts = GF.Members.basic_member_counts(org_id)

        Ash.DataLayer.Simple.set_data(query, [
          struct!(__MODULE__, %{
            members_count: counts.active_members
          })
        ])
      else
        query
      end
    end
  end
end

Is this the right approach? What exactly goes in the prepare block to make this work?

ZachDaniel•2y ago

Hmm...not sure why its returning nil for the result, as that pattern looks generally correct The way you're doing it is a reasonable way to do what you're looking to do. Although likely what I'd do is add calculations and just return struct!(__MODULE__, %{}) from the read. I'd populate a random UUID also, as resources expect that. Even in cases like this it can be useful and is cheap enough to do I think. i.e struct!(__MODULE__, %{id: Ash.UUID.generate()}) Have you confirmed that your hook there is being called? you said its returning nil, but is your call to set_data definitely happening for example? If you call read_one does it return a list? **read instead of read_one?

moxleyOP•2y ago

Okay, that helps to know if I'm on the right track. The hook you mention, is that the prepare block? Yes, that's getting called. In fact, it's called twice. The first time, it has an actor, and the second time, it doesn't. I suspect the second call is the one that's being used for the return value. I added id: Ash.UUID.generate() too.

ZachDaniel•2y ago

hm...its getting called twice ??

moxleyOP•2y ago

Yeah, I don't know why.

ZachDaniel•2y ago

try putting it in a before_action block actually since you don't technically want it to happen on query validation it could mean that somewhere we are rerunning query preparations, which isn't necessarily that big of a bug since anything intensive should be behind a before_action block there is an Ash.Query.before_action just like Ash.Changeset

moxleyOP•2y ago

Does the Ash.Query.before_action() go inside the prepare block? After some debugging, it shows that the prepare block gets called both for Ash.Query.for_read((), and API.read_one!(). So here's the action def:

  actions do
    read :read do
      get? true
      primary? true

      prepare fn query, context ->
        IO.puts("read prepare")

        Ash.Query.before_action(query, fn query ->
          IO.puts("before action")

          if context.actor do
            IO.puts("actor present")
            org_id = context.actor.org_id
            counts = GF.Members.basic_member_counts(org_id)

            Ash.DataLayer.Simple.set_data(query, [
              struct!(__MODULE__, %{
                id: Ash.UUID.generate(),
                members_count: counts.active_members
              })
            ])
          else
            IO.puts("No actor present")
            query
          end
        end)
      end
    end
  end

  actions do
    read :read do
      get? true
      primary? true

      prepare fn query, context ->
        IO.puts("read prepare")

        Ash.Query.before_action(query, fn query ->
          IO.puts("before action")

          if context.actor do
            IO.puts("actor present")
            org_id = context.actor.org_id
            counts = GF.Members.basic_member_counts(org_id)

            Ash.DataLayer.Simple.set_data(query, [
              struct!(__MODULE__, %{
                id: Ash.UUID.generate(),
                members_count: counts.active_members
              })
            ])
          else
            IO.puts("No actor present")
            query
          end
        end)
      end
    end
  end

The read_one!() is still returning nil, and read!() returns an empty list. The "before_action" and "actor present" debug statements are displayed in the test output. The "No actor present" is no longer displayed.

ZachDaniel•2y ago

something very strange is happening then can you inspect the value of query.__validated_for_action__ at the beginning of your preparation?

moxleyOP•2y ago

query.__validated_for_action__ : nil It's nil

ZachDaniel•2y ago

both times its called? The reproduction here seems pretty simple, I'll take a look at it this evening or tomorrow morning. For now, what you actually want to do is pass the actor when building the query

moxleyOP•2y ago

Okay, I tried something. I commented out the multitenancy definition, and now it's returning the struct.

ZachDaniel•2y ago

🤔 huh huh that doesn't make a lot of sense what was the multitenancy definition?

moxleyOP•2y ago

Oh wait. It's not that. I commented out the Ash.Query.set_tenant(ctx.org.id) in the test

ZachDaniel•2y ago

so strange

moxleyOP•2y ago

That's where the issue stems

ZachDaniel•2y ago

so if a tenant is set, for some reason, its calling your query preparations twice So do for_read(...., actor: actor) Using the code interface, for example, solves that problem, but that is actually the best way to pass things in when building queries i.e Query.for_read(..., actor: actor, authorize?: authorize?, tenant: tenant) same for change sets, and we carry it over it just doesn't technically matter if you don't use the actor in preparations/changesets. But...for 3.0 maybe I'll actually make that error, and require passing it when building the query, to avoid this confusion

moxleyOP•2y ago

Or, another way to get it to pass is to leave in the Ash.Query.set_tenant(ctx.org.id), but comment out the multitenancy section.

ZachDaniel•2y ago

good to know so that means its not in the tenant setting code its in the "doing multitenant stuff" code

moxleyOP•2y ago

About the API.read!() call, I realized that about the redundant actor specification, and removed it, so that it's only in the for_read() call. I did that earlier.

ZachDaniel•2y ago

wow, okay, so this is actually pretty interesting there is an interaction here I didn't consider

moxleyOP•2y ago

So here's my test now:

      dashboard =
        Dashboard
        |> Ash.Query.set_tenant(ctx.org.id)
        |> Ash.Query.for_read(:read, %{}, actor: ctx.member)
        |> GF.Ash.read_one!()

      dbg(dashboard)

      dashboard =
        Dashboard
        |> Ash.Query.set_tenant(ctx.org.id)
        |> Ash.Query.for_read(:read, %{}, actor: ctx.member)
        |> GF.Ash.read_one!()

      dbg(dashboard)

And based on what you said, the set_tenant() call is unecessary, if I pass the tenant to the for_read() call...

ZachDaniel•2y ago

Yep okay nvm I thought I had found it but I hadn't but also I'm investigating in safari on an ipad 😆

moxleyOP•2y ago

So now I'm at this in the test:

      dashboard =
        Dashboard
        |> Ash.Query.for_read(:read, %{}, actor: ctx.member, tenant: ctx.org.id)
        |> GF.Ash.read_one!()

      dbg(dashboard)

      dashboard =
        Dashboard
        |> Ash.Query.for_read(:read, %{}, actor: ctx.member, tenant: ctx.org.id)
        |> GF.Ash.read_one!()

      dbg(dashboard)

ZachDaniel•2y ago

I believe this will be easy for me to debug. because it should be easy to reproduce actually, lets try something real quick can you raise an error if actor is nil and show me the stacktrace?

moxleyOP•2y ago

Raise it if the actor is nil? It's not nil though. Do you mean in the before_action() fn?

ZachDaniel•2y ago

maybe I need to regroup 😆 is it still getting called twice? but now both times the actor is not nil?

moxleyOP•2y ago

I'ts not getting called twice now, because I added the before_action() call. The prepare is getting called twice, but the before_action() anon fn is getting called once:

  actions do
    read :read do
      get? true
      primary? true

      prepare fn query, context ->
        IO.inspect(query.__validated_for_action__, label: "query.__validated_for_action__ ")

        Ash.Query.before_action(query, fn query ->
          IO.puts("before action")

          if context.actor do
            IO.puts("actor present")
            org_id = context.actor.org_id
            counts = GF.Members.basic_member_counts(org_id)

            Ash.DataLayer.Simple.set_data(query, [
              struct!(__MODULE__, %{
                id: Ash.UUID.generate(),
                members_count: counts.active_members
              })
            ])
          else
            raise "No actor present"
          end
        end)
      end
    end
  end

  actions do
    read :read do
      get? true
      primary? true

      prepare fn query, context ->
        IO.inspect(query.__validated_for_action__, label: "query.__validated_for_action__ ")

        Ash.Query.before_action(query, fn query ->
          IO.puts("before action")

          if context.actor do
            IO.puts("actor present")
            org_id = context.actor.org_id
            counts = GF.Members.basic_member_counts(org_id)

            Ash.DataLayer.Simple.set_data(query, [
              struct!(__MODULE__, %{
                id: Ash.UUID.generate(),
                members_count: counts.active_members
              })
            ])
          else
            raise "No actor present"
          end
        end)
      end
    end
  end

When I comment out the multitenancy block, the prepare block only gets called once.

ZachDaniel•2y ago

But it still doesn't work right?

moxleyOP•2y ago

It does work for that case Found it! I needed to add the tenant attribute value to the struct:

          Ash.DataLayer.Simple.set_data(query, [
            struct!(__MODULE__, %{
              id: Ash.UUID.generate(),
              members_count: counts.active_members,
              org_id: org_id
            })
          ])

          Ash.DataLayer.Simple.set_data(query, [
            struct!(__MODULE__, %{
              id: Ash.UUID.generate(),
              members_count: counts.active_members,
              org_id: org_id
            })
          ])

I should have thought of that. The prepare block is still called twice.

ZachDaniel•2y ago

Okay, yeah that makes sense Sounds like we probably need some helpers for this potentially like helpers for constructing manually returned records, where it sets some metadata that the simple data layer can yell at you about

moxleyOP•2y ago

Cool.

ZachDaniel•2y ago

Sorry I didn't catch that sooner

moxleyOP•2y ago

So now I'm on to testing the GQL query...

ZachDaniel•2y ago

🤞

moxleyOP•2y ago

I'm getting this in the logs:

"Cannot query field \"getAdminDashboard\" on type \"RootQueryType\"

"Cannot query field \"getAdminDashboard\" on type \"RootQueryType\"

ZachDaniel•2y ago

Is this in a new api>?

moxleyOP•2y ago

My graphql section looks like this:

  graphql do
    type :admin_dashboard

    queries do
      get :get_admin_dashboard, :read do
        identity false
      end
    end
  end

  graphql do
    type :admin_dashboard

    queries do
      get :get_admin_dashboard, :read do
        identity false
      end
    end
  end

No, it's an existing api

ZachDaniel•2y ago

is it in the registry?

moxleyOP•2y ago

Yep

ZachDaniel•2y ago

hmm....from a gql perspective this shouldn't be any different than any other thing maybe restart/recompile?

moxleyOP•2y ago

I'll try force-compile

ZachDaniel•2y ago

does it show up when you look at the schema?

moxleyOP•2y ago

Looks like force-compile resolved that. I'm onto another issue...

ZachDaniel•2y ago

strange, that shouldn't be necessary what's up?

moxleyOP•2y ago

I think it's just a bad test setup...

ZachDaniel•2y ago

I think what you'll also want to do is make those fields into calculations, now that you've got the action returning. That way when a subset of fields are requested over gql it won't calculate all of them

moxleyOP•2y ago

Okay, I see. Yeah, try that out.

ZachDaniel•2y ago

👍 LMK if you run into anything else/if the issue you mentioned isn't due to your tests 😆

moxleyOP•2y ago

The GraphQL query is working. Thanks for your help! I might need help with the calculations, but let's see how far I can get...

ZachDaniel•2y ago

I can give you a quick template to get you started, unless you'd like to figure it out on your own

moxleyOP•2y ago

That would be helpful!

ZachDaniel•2y ago

defmodule YourApp.YourApi.AdminDashboard.Calculations.MemberCounts do
  use Ash.Calculations

  # This is technically not necessary because you always select org_id in your manual action
  # but is good form
  def select(_, _, _), do: [:org_id]

  def calculate(records, _, _) do
     # There will only ever be one in your setup
     Enum.map(records, fn record -> 
        member_counts(record.org_id)
     end)
  end
end

defmodule YourApp.YourApi.AdminDashboard.Calculations.MemberCounts do
  use Ash.Calculations

  # This is technically not necessary because you always select org_id in your manual action
  # but is good form
  def select(_, _, _), do: [:org_id]

  def calculate(records, _, _) do
     # There will only ever be one in your setup
     Enum.map(records, fn record -> 
        member_counts(record.org_id)
     end)
  end
end

Then in your admin dashboard resource:

calculations do
  calculate :member_counts, :map, YourApp.YourApi.AdminDashboard.Calculations.MemberCounts
end

calculations do
  calculate :member_counts, :map, YourApp.YourApi.AdminDashboard.Calculations.MemberCounts
end

moxleyOP•2y ago

I see. Nice! I converted it to a calculation, and it's working. One small question: In the read prepare block, I'm getting the tenant value from the actor, because I couldn't find it another way. Is ther a way to get the tenant without having to get it from the actor?

ZachDaniel•2y ago

It should be in query.tenant

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