Test code to take incoming GraphQL-Go query and inspect the AST for sub fields

graphql_inspect_query.go

package main

import (
  "encoding/json"
	"fmt"
	"log"
	"github.com/graphql-go/graphql"
  "github.com/graphql-go/graphql/language/ast"
)

func scanField(f *ast.Field, prefix string) {
  fmt.Printf("%s%s  --  %#v\n", prefix, f.Name.Value, f)
  if f.SelectionSet != nil {
    for _, s  := range f.SelectionSet.Selections {
      if k, ok := s.(*ast.Field); ok {
        scanField(k, prefix + " ")
      }
    }
  }
}

func main() {
	// Schema
  personObject := graphql.NewObject(graphql.ObjectConfig{Name: "Person",
    Fields: graphql.Fields{"name": &graphql.Field{
			Type: graphql.String,
		}},
  })

  personObject.AddFieldConfig("friend", &graphql.Field{
    Name: "Friend",
    Type: personObject})

	fields := graphql.Fields{
		"hello": &graphql.Field{
			Type: graphql.String,
			Resolve: func(p graphql.ResolveParams) (interface{}, error) {
				return "world", nil
			},
		},
    "person" : &graphql.Field{
      Type: personObject,
      Resolve: func(p graphql.ResolveParams) (interface{}, error) {
        fmt.Printf("main field: %#v\n", p.Info.FieldASTs)
        for _, i := range p.Info.FieldASTs {
          scanField(i, "")
        }
				return map[string]interface{}{"name" : "bob", "friend" : map[string]interface{}{ "name" : "Joe",
          "friend" : map[string]interface{}{ "name" : "Sam" },
        } }, nil
			},
    },
	}
	rootQuery := graphql.ObjectConfig{Name: "RootQuery", Fields: fields}
	schemaConfig := graphql.SchemaConfig{Query: graphql.NewObject(rootQuery)}
	schema, err := graphql.NewSchema(schemaConfig)
	if err != nil {
		log.Fatalf("failed to create new schema, error: %v", err)
	}

	// Query
	query := `
		{
      person {
        name
        friend { name
          friend {
            name
          }
        }
      }
		}
	`
	params := graphql.Params{Schema: schema, RequestString: query}
	r := graphql.Do(params)
	if len(r.Errors) > 0 {
		log.Fatalf("failed to execute graphql operation, errors: %+v", r.Errors)
	}
	rJSON, _ := json.Marshal(r)
	fmt.Printf("%s \n", rJSON) // {“data”:{“hello”:”world”}}
}