Custom Scalar Type

main.go

package main
import (    "encoding/json"    "fmt"    "log"
    "github.com/graphql-go/graphql"    "github.com/graphql-go/graphql/language/ast")
type CustomID struct {    value string}
func (id *CustomID) String() string {    return id.value}
func NewCustomID(v string) *CustomID {    return &CustomID{value: v}}
var CustomScalarType = graphql.NewScalar(graphql.ScalarConfig{    Name:        "CustomScalarType",    Description: "The `CustomScalarType` scalar type represents an ID Object.",    // Serialize serializes `CustomID` to string.    Serialize: func(value interface{}) interface{} {        switch value := value.(type) {        case CustomID:            return value.String()        case *CustomID:            v := *value            return v.String()        default:            return nil        }    },    // ParseValue parses GraphQL variables from `string` to `CustomID`.    ParseValue: func(value interface{}) interface{} {        switch value := value.(type) {        case string:            return NewCustomID(value)        case *string:            return NewCustomID(*value)        default:            return nil        }    },    // ParseLiteral parses GraphQL AST value to `CustomID`.    ParseLiteral: func(valueAST ast.Value) interface{} {        switch valueAST := valueAST.(type) {        case *ast.StringValue:            return NewCustomID(valueAST.Value)        default:            return nil        }    },})
type Customer struct {    ID *CustomID `json:"id"`}
var CustomerType = graphql.NewObject(graphql.ObjectConfig{    Name: "Customer",    Fields: graphql.Fields{        "id": &graphql.Field{            Type: CustomScalarType,        },    },})
func main() {    schema, err := graphql.NewSchema(graphql.SchemaConfig{        Query: graphql.NewObject(graphql.ObjectConfig{            Name: "Query",            Fields: graphql.Fields{                "customers": &graphql.Field{                    Type: graphql.NewList(CustomerType),                    Args: graphql.FieldConfigArgument{                        "id": &graphql.ArgumentConfig{                            Type: CustomScalarType,                        },                    },                    Resolve: func(p graphql.ResolveParams) (interface{}, error) {                        // id := p.Args["id"]                        // log.Printf("id from arguments: %+v", id)                        customers := []Customer{                            Customer{ID: NewCustomID("fb278f2a4a13f")},                        }                        return customers, nil                    },                },            },        }),    })    if err != nil {        log.Fatal(err)    }    query := `        query {            customers {                id            }        }    `    /*        queryWithVariable := `            query($id: CustomScalarType) {                customers(id: $id) {                    id                }            }        `    */    /*        queryWithArgument := `            query {                customers(id: "5b42ba57289") {                    id                }            }        `    */    result := graphql.Do(graphql.Params{        Schema:        schema,        RequestString: query,        VariableValues: map[string]interface{}{            "id": "5b42ba57289",        },    })    if len(result.Errors) > 0 {        log.Fatal(result)    }    b, err := json.Marshal(result)    if err != nil {        log.Fatal(err)    }    fmt.Println(string(b))}