cayleygraph/cayley · error

unknown selection type: %T

Error message

unknown selection type: %T

What it means

setToFields switches over the ast.Selection types it understands (fields, fragments) and any other selection type falls into a default case that errors, naming the concrete Go type encountered. This indicates a selection kind the parser does not implement.

Source

Thrown at query/graphql/graphql.go:464

	}
	for _, s := range set.Selections {
		switch sel := s.(type) {
		case *ast.Field:
			fld, err := convField(sel, labels)
			if err != nil {
				return nil, false, err
			}
			if fld.Via == quad.IRI(AnyKey) {
				if len(set.Selections) != 1 {
					return nil, false, fmt.Errorf("expand all cannot be used with other fields")
				} else if len(fld.Has) != 0 || len(fld.Fields) != 0 {
					return nil, false, fmt.Errorf("filters inside expand all are not supported")
				}
				return nil, true, nil
			}
			out = append(out, fld)
		default:
			return nil, false, fmt.Errorf("unknown selection type: %T", s)
		}
	}
	return
}

func stringToVia(s string) (_ quad.IRI, rev bool) {
	if len(s) > 0 && s[0] == '~' {
		rev = true
		s = s[1:]
	}
	if len(s) > 2 && s[0] == '<' && s[len(s)-1] == '>' {
		s = s[1 : len(s)-1]
	}
	return quad.IRI(s), rev
}

func argsToHas(dst []has, args []*ast.Argument, rev bool, labels []quad.Value) (out []has, err error) {
	out = dst

View on GitHub (pinned to 81dcd7d73e)

Solutions

1. Upgrade/downgrade Cayley so its parser and converter versions match
2. Check which type appears in the message and avoid that GraphQL construct
3. Use standard field and inline-fragment selections only

// Validate only standard field/fragment selections are used
function usesOnlySupportedSelections(sel) {
  return (sel || []).every(s => ['Field','InlineFragment'].includes(s.kind));
}

const isSupportedSelection = (s) => s && (s.kind === 'Field' || s.kind === 'InlineFragment');

try {
  result, err := engine.Parse(ctx, q)
  if err != nil {
    if strings.HasPrefix(err.Error(), "unknown selection type") {
      log.Printf("unsupported GraphQL construct: %v", err)
      // degrade or upgrade library
    }
    return err
  }
}

When it happens

Trigger: A parsed document whose SelectionSet contains a selection type other than *ast.Field or *ast.InlineFragment handling in the switch — e.g. unusual AST shapes produced by certain parser versions or hand-crafted ASTs passed to Parse.

Common situations: Version drift where the gqlparser emits a new selection type; constructing ast.Selection values manually in tests; document features (rare constructs) unsupported by the converter.

Understand the failure class

Background: "invalid response format", "malformed payload", "missing data field": when an API returns 200 but the response shape is wrong — this error's family across 23 libraries.

Related errors

• unexpected value type for %v: %T
• unsupported query type: %T
• token not valid
• gae quad: token not valid
• must execute a Step

AI-assisted analysis of cayleygraph/cayley@81dcd7d73e (2026-09-06). Data as JSON: /api/errors/cb6707f57d6996b0. Report an issue: GitHub.