Using Ash.Query.add_error()

moxley

I’m creating a read AshGraphql query, and I want it to return an error for certain conditions. When I call Ash.Query.add_error(query, "some error message") or similar in the action prepare, the GraphQL query returns:

%{
  "data" => %{"listMemberSelfSubscriptions" => nil},
  "errors" => [
    %{
      "locations" => [%{"column" => 3, "line" => 2}],
      "message" => "Something went wrong. Unique error id: `dd416b26-3ffd-4731-aae3-279a2131cb05`",
      "path" => ["listMemberSelfSubscriptions"]
    }
  ]
}

It always returns a generic “Something went wrong”. How do I pass an error message to the response?

If I use raw Ash.Query without AshGraphql, calling Ash.Query.add_error() results in an UnknownError:

 %Ash.Error.Unknown{
   errors: [
     %Ash.Error.Unknown.UnknownError{
       error: ": Test error",
       field: nil,
       value: nil,
       splode: Ash.Error,
       bread_crumbs: [],
       vars: [],
       path: [],
       stacktrace: #Splode.Stacktrace<>,
       class: :unknown
     }
   ]
 }

For that matter, how do I use Ash.Query.add_error()? There’s no documentation for it:

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/ash #ash-graphql #ash-query

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2024-12-08 06:53:16 UTC

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moxley

I tried this as well: Error Handling — ash v3.29.3, but Ash.Error.Changes.Required.new/1 is not defined.

So then I used struct literal syntax, and it resulted in the error appearing in the AshGraph response:

prepare fn query, _context do
  error =
    %Ash.Error.Changes.Required{
      field: :foo,
      type: :attribute
    }

  Ash.Query.add_error(query, error)
end

...

resp_body #=> %{
  "data" => nil,
  "errors" => [
    %{
      "code" => "required",
      "fields" => ["foo"],
      "locations" => [%{"column" => 3, "line" => 2}],
      "message" => "is required",
      "path" => ["listMemberSelfSubscriptions"],
      "short_message" => "is required",
      "vars" => []
    }
  ]
}

I think if I play around with one of the other Ash error modules, I’ll find what I need to make this work correctly.

Post #1

zachdaniel

Creator of Ash

Ahh, that doc is out of date for 3.0, sorry! Using exception modules like that is “the way”, the only difference is that all our errors are exceptions, so you’d use .exception as if it was any other error. It’s all powered by the library (which was extracted out of Ash) called Splode API Reference — splode v0.3.1

Then, these errors have a specific protocol defined for them to allow them to be exposed over an API (differs depending on the API). You can also define your own errors and use those, if you implement the appropriate protocol.

You can see examples here: ash_graphql/lib/error.ex at main · ash-project/ash_graphql · GitHub

Post #2

zachdaniel

Creator of Ash

Did some mild reconstruction of the relevant docs and type specs. The add_error functions point to the error handling guide, and more examples of returning errors have been added to that guide as well. Finally, the last section links to the relevant protocols that must be implemented to show custom errors in APIs.

Post #3

zachdaniel

Creator of Ash

Since a release was just done yesterday, I was able to publish these new docs, so the hexdocs for Ash should reflect these updates as of now.

Post #4

zachdaniel

Creator of Ash

As you yourself have pointed out, there is still a very long way to go for docs in general, but I’ve begun the (slow and steady) process of beefing up docs, adding links, type specs function docs etc. This will continue for a while. Others in the community are also pitching in which is great. Shout out to @allenwyma especially.

Post #5