how to run a function before all generated resolvers ?

[moshir]

Which Category is your question related to?
@function directive

Amplify CLI Version
3.17.0

What AWS Services are you utilizing?
lambda, dynamodb

Provide additional details e.g. code snippets

As an example, i have a custom lambda function which performs custom authorization checks before an action. (@auth directive does not match my requirements, where users can belong to hundreds of groups). The function acts as a gate keeper, throwing an Unautorized exception when the user is not allowed to perform the action on a resource, otherwise forwarding the initial request.

I'd like to run this "gatekeeper" function before the generated vtl runs.
As per the documentation, the @function directive overrides the vtl.
Is it possible to implement some sort of pipeline resolver mixing lambda and vtl.

Another example might be to use a custom lambda function to filter items out from a vtl.

I was thinking about a custom directives like

enum Action{
  CREATE 
 UPDATE 
 DELETE
 ALL
}
directive @before(actions:[Action], function:String!) on OBJECT

That would be used as follow:

type MyType 
@model
@before(actions:[ALL], function : "check"){
   id : ID! 
  name : String!
  description : String
}

When query/mutation is run, the check function is called with all initial arguments, the function performs whatever logic it needs to do and can also update the arguments, including $context.stash and the execution resumes to the generated VTL.

[yuth]

Amplify CLI out of the box won't have support for this but a custom directive can be written as you mentioned. We recently added support for custom transformer plugin. We have docs for transformer plugin and docs for how to use these custom plugins in PR aws-amplify/docs#992.

We also have an RFC for supporting pipeline resolvers in a generic way. Feel free to comment there to so the issue includes your use case mentioned here.

The other alternative is to chain @function directive as documented under Chaining functions section.

[deagudelo]

Did you solve this issue? Is that directive available somewhere? What about an @after following similar logic?

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