Schema extracting does not complete when input and result use the same type that has nested data types

[oofp]

Here as an example:

data UserType = UserManager | UserTechLead | UserDev | UserQA deriving (Generic, GQLType)
data UserName = UserName 
  { firstName :: Text
  , lastName :: Text
  } deriving (Generic, GQLType)
data User = User
  { userName :: UserName
  , userType :: UserType
  , userDsc :: Text
  } deriving (Generic, GQLType)   
data Query m = Query
  { user :: User -> m User
  } deriving (Generic, GQLType)
resolveUserQ :: User -> ResolverQ e IO User
resolveUserQ usr = return usr  

UserName is nested inside User. It compiles successfully but schema retrieval stuck

[kamek-pf]

I think Morpheus is currently lacking support for nested input types.
I can reproduce this just by having nested input types, regardless of what the return type is.

[oco-adam]

I can also reproduce this just by having nested input object types. Is there a suggested workaround for this other than flattening everything to remove nesting?

[kamek-pf]

I found solution.
If you need to use a record as a nested input, instead of deriving GQLType, you can write the instance manually and set the proper kind:

data MainThing = MainThing
   { input :: NestedThing
   }
   deriving (Generic, Show, GQLType)

-- Nested fields, requires manually deriving GQLType to set the INPUT kind
data NestedThing = NestedThing
   { field1 :: Text
   , field2 :: Text
   }
   deriving (Generic, Show)

instance GQLType NestedThing where
   type KIND NestedThing = INPUT
   description _ = Just "Nested thing docs"

Maybe we could send a PR to update the docs and make this more obvious ?

[oco-adam]

@kamek-pf I can confirm that your solution worked for me - thank you! :)

I'm a Haskell beginner and it definitely would have helped me if this was included in the docs, so I think a PR to update the docs would be a good idea.

[nalchevanidze]

@kamek-pf @oco-adam it is not nesting, problem is that you use Output Type as Input Type. that is not allowed in GraphQL.

currently the library does not report an error message about this violation, which will be fixed in the future

[nalchevanidze]

now you can fix it with GQLTypeOptions supports new option prefixInputType.

it will fix your problem, if you derive them with it (like in this example)

data UserType = UserManager | UserTechLead | UserDev | UserQA deriving (Generic, GQLType)

data UserName = UserName 
  { firstName :: Text
  , lastName :: Text
  } deriving (Generic)

instance GQLType UserName where
    typeOptions _ opt = opt {prefixInputType = True}

data User = User
  { userName :: UserName
  , userType :: UserType
  , userDsc :: Text
  } deriving (Generic, GQLType)   

data Query m = Query
  { user :: User -> m User
  } deriving (Generic, GQLType)


resolveUserQ :: User -> ResolverQ e IO User
resolveUserQ usr = return usr  

so will graphql generate following schema.

enum UserType {
  UserManager 
  UserTechLead 
  UserDev 
  UserQA
} 

input InputUserName { 
  firstName : String!
  lastName : String!
} 

type UserName { 
  firstName : String!
  lastName : String!
} 

type User { 
  userName : UserName!
  userType : UserType!
  userDsc : String!
}   

type Query {
  user ( 
    userName : InputUserName!
    userType : UserType!
    userDsc : String!
  ): User
} 

notice:

1. argument userNameuses input type InputUserName
2. we don't have to generate input type for type User since its fields are represented as arguments

otherwise you will get error message :

{
  "errors": [
    {
      "message": "It appears that the Haskell type \"UserName\" was used as both input and output type, which is not allowed by GraphQL specifications.\n\n If you enable \"{ prefixInputType = True }\" in \"GQLType.typeOptions\", the compiler can generate a new input type \"InputUserName\" to solve this problem.",
      "locations": []
    }
  ]
}