Resolver

In GraphQL every property needs a resolver. The resolver is the piece of system logic, required to resolve the response graph. Operations, Extension Properties and Union Properties accept resolver, which allows schema creators to configure schema behaviour.

Schema

Resolver clause accepts kotlin function and returns its DSL item, which is entry point for additional customization of resolver:

Example

query("item") {
    resolver { -> Item(id, "Item Name") }
}

Arguments

The withArgs closure has a method arg that exposes the possibility to customize argument default values. The default value is automatically used if query doesn't provide any, and is matched by argument name.

Example

KGraphQL.schema {
    query("data") {
        resolver { int: Int, string: String? -> int }.withArgs {
            arg<Int> { name = "int"; defaultValue = 33 }
        }
    }
}

Context

To get access to the context object, you can request for the Context object within your resolver.

When providing Context as an argument for your resolver, it will be skipped and not published to your API, but KGraphQL will make sure to provide it to the resolver, so you can use it like the following example:

Example

query("hello") {
    resolver { country: String, ctx: Context ->
        val user = ctx.get<User>()
        Hello(label = "Hello ${user?.name ?: "unknown"}")
    }
}

Then in your query execution process you will provide a Context like shown here:

Example

val query = """
    query fetchHelloLabel($country: String!) {
        hello(country: $country) {
            label
        }
    }
"""
val variables = """
    {"country": "English"}
"""
val user = User(id = 1, name = "Username")
val ctx = context {
    +user
}
schema.execute(query, variables, ctx)

Node

Similar to Context, resolvers can also request for the Node object, which is a representation of the current node in the response graph.

ExampleQueryResponse

data class Director(val firstName: String, val lastName: String)
data class Film(val title: String, val director: Director)

val schema = KGraphQL.schema {
    configure { useDefaultPrettyPrinter = true }

    query("films") {
        resolver { ->
            listOf(
                Film("Prestige", Director("Christopher", "Nolan")),
                Film("Se7en", Director("David", "Fincher"))
            )
        }
    }
    type<Film> {
        property("fullPath") {
            resolver { _: Film, node: Execution.Node -> node.fullPath.joinToString(".") }
        }
    }
    type<Director> {
        property("fullPath") {
            resolver { _: Director, node: Execution.Node -> node.fullPath.joinToString(".") }
        }
    }
}

query {
    films {
        title
        fullPath
        director {
            firstName
            lastName
            fullPath
        }
    }
}

{
  "data" : {
    "films" : [ {
      "title" : "Prestige",
      "fullPath" : "films.0.fullPath",
      "director" : {
        "firstName" : "Christopher",
        "lastName" : "Nolan",
        "fullPath" : "films.0.director.fullPath"
      }
    }, {
      "title" : "Se7en",
      "fullPath" : "films.1.fullPath",
      "director" : {
        "firstName" : "David",
        "lastName" : "Fincher",
        "fullPath" : "films.1.director.fullPath"
      }
    } ]
  }
}