Try and fail to implement a directive @constraint

[jmfayard]

📝 Description

Helo, I tried and failed to implement a GraphQL directive as explained here
-> https://opensource.expediagroup.com/graphql-kotlin/docs/schema-generator/customizing-schemas/directives#custom-directives

Dariusz Kuc asked me on Slack to provide a sample that shows the issue and here it is.

Reproducing steps:

• run the :ktor-server:run Gradle task
• fetch the GraphQL schema

Expected:

"This GraphQL directive allows to add constraints to the GraphQL Schema - https://www.apollographql.com/blog/backend/validation/graphql-validation-using-directives/"
directive @constraint(format: String!, maxLength: Int!, minLength: Int!, pattern: String!) on VARIABLE_DEFINITION | FIELD_DEFINITION | INPUT_OBJECT

input DirectiveInput {
    deviceId: String! @constraint(minLength: 8, maxLength: 16)
    email: String! @constraint(format: "email")
}


type DirectivePayload {
    deviceId: String! @constraint(minLength: 8, maxLength: 16)
    email: String! @constraint(format: "email")
}

Got:

"This GraphQL directive allows to add constraints to the GraphQL Schema - https://www.apollographql.com/blog/backend/validation/graphql-validation-using-directives/"
directive @constraint(format: String!, maxLength: Int!, minLength: Int!, pattern: String!) on VARIABLE_DEFINITION | FIELD_DEFINITION | INPUT_OBJECT

input DirectiveInput {
    deviceId: String!
    email: String!
}


type DirectivePayload {
    deviceId: String!
    email: String!
}

🔗 Related Issues

[dariuszkuc]

How are you printing the schema? When I updated ktorGraphQLSchema.kt to print it before returning new schema object (and also added ARGUMENT_DEFINITION to the directive target locations)

fun getGraphQLObject(): GraphQL {
    println(graphQLSchema.print()) // print out SDL
    return GraphQL.newGraphQL(graphQLSchema).build()
}

I got following schema printed out (omitted non interesting parts)

"This GraphQL directive allows to add constraints to the GraphQL Schema - https://www.apollographql.com/blog/backend/validation/graphql-validation-using-directives/"
directive @constraint(format: String!, maxLength: Int!, minLength: Int!, pattern: String!) on FIELD_DEFINITION | ARGUMENT_DEFINITION | INPUT_OBJECT | INPUT_FIELD_DEFINITION

type DirectivePayload {
  deviceId: String! @constraint(format : "", maxLength : 16, minLength : 8, pattern : "")
  email: String! @constraint(format : "email", maxLength : 2147483647, minLength : 1, pattern : "")
}

type Mutation {
  directive(input: DirectiveInput!): DirectivePayload!
  login(aliasUUID: String, email: String! @constraint(format : "email", maxLength : 2147483647, minLength : 1, pattern : ""), password: String!): AuthPayload!
}

input DirectiveInput {
  deviceId: String! @constraint(format : "", maxLength : 16, minLength : 8, pattern : "")
  email: String! @constraint(format : "email", maxLength : 2147483647, minLength : 1, pattern : "")
}

[jmfayard]

I was using IntelliJ's plugin for GraphQL to generate the schema https://plugins.jetbrains.com/plugin/8097-graphql

This was the issue, this plugin does not print the directive

I added a unit test that re-generates the schema using graphQLSchema.print() and it all works

Thanks a lot for your help @dariuszkuc

[dariuszkuc]

Pretty sure that plugin (same as most of the tooling) relies on introspection to get the schema (which does not include directive information, see graphql/graphql-spec#300). Generally you will only be able to get the schema with the directives if you explicitly print it out (e.g. in spring-server we expose /sdl endpoint).

[jmfayard]

Follow up: #1351