Selection Sets Support

[Hale-ma]

Hi, I enjoy using this library developing my graphql server. I would like to know is there any support for Selection Sets of query? Define different behavior in a function for query with different Selection Sets may enhance the performance. For instance, a query that only lookup a few field may only need a sample SQL to finish while looking for extra field for this fragment may need to have other logic to calculate the field to return . If I can pass the return field to my function, I can do different logic. However, seems query.FieldFunc("name",func) does not support this.

[kevinmichaelchen]

Seems like related code: argsToJson and parseSelectionSet

thunder/graphql/parser.go

Lines 91 to 109 in babf75b

	func argsToJson(input []*ast.Argument, vars map[string]interface{}) (map[string]interface{}, error) {
	args := make(map[string]interface{})
	for _, arg := range input {
	name := arg.Name.Value
	if _, found := args[name]; found {
	return nil, NewClientError("duplicate arg")
	}
	value, err := valueToJson(arg.Value, vars)
	if err != nil {
	return nil, err
	}
	args[name] = value
	}
	return args, nil
	}
	// parseSelectionSet takes a grapqhl-go selection set and converts it to a
	// simplified *SelectionSet, bindings vars
	func parseSelectionSet(input *ast.SelectionSet, globalFragments map[string]*Fragment, vars map[string]interface{}) (*SelectionSet, error) {

[uripre]

+1 for that

[uripre]

Probably related to #200 and #201