cayleygraph/cayley · error

no rules for struct: %v

Error message

no rules for struct: %v

What it means

After loading rules, writeAsQuads checks that the struct actually produced field rules. An empty rule set means the struct has no mapped fields (all ignored or no usable tags), so there is nothing to serialize into quads. The error names the offending struct type.

Source

Thrown at schema/writer.go:163

		kind == reflect.Int16 || kind == reflect.Uint16 ||
		kind == reflect.Int8 || kind == reflect.Uint8 {
		return quad.Int(rv.Int()), nil
	} else if kind == reflect.Float64 || kind == reflect.Float32 {
		return quad.Float(rv.Float()), nil
	} else if kind == reflect.Bool {
		return quad.Bool(rv.Bool()), nil
	}
	// TODO(dennwc): support maps
	if kind != reflect.Struct {
		return nil, fmt.Errorf("unsupported type: %v", rt)
	}
	// get conversion rules for this struct type
	rules, err := w.c.rulesFor(rt)
	if err != nil {
		return nil, fmt.Errorf("can't load rules: %v", err)
	}
	if len(rules) == 0 {
		return nil, fmt.Errorf("no rules for struct: %v", rt)
	}
	// get an ID from the struct value
	id, err := w.c.idFor(rules, rt, rv, "")
	if err != nil {
		return nil, err
	}
	if id == nil {
		id = w.c.genID(prv.Interface())
	}
	// save a node ID to avoid loops
	switch prv.Kind() {
	case reflect.Ptr, reflect.Map:
		ptr := prv.Pointer()
		w.seen[ptr] = id
	}
	if err = w.writeValueAs(id, rv, "", rules); err != nil {
		return nil, err
	}

View on GitHub (pinned to 81dcd7d73e)

Solutions

1. Add at least one mapped field with a valid schema tag to the struct
2. Review ignore tags - remove `quad:"-"` from fields that should be stored
3. Skip writing structs that intentionally carry no data, or handle them with raw quads instead

Example fix

// before
type Doc struct {
    Internal string `quad:"-"`
}
// after
type Doc struct {
    Internal string `quad:"-"`
    Name     string `tag:"name"`
}

rules, err := cfg.RulesFor(reflect.TypeOf(doc))
if err != nil { return err }
if len(rules) == 0 {
    return fmt.Errorf("struct %T has no schema-mapped fields", doc)
}

if _, err := w.WriteAsQuads(qs, doc); err != nil {
    if strings.Contains(err.Error(), "no rules for struct") {
        // ensure the struct has at least one tagged, supported field
        return err
    }
    return err
}

When it happens

Trigger: Writing a struct whose every field is excluded from schema mapping (e.g. all tagged `quad:"-"`) or which contains only unsupported/ignored fields.

Common situations: Marker/empty structs accidentally passed to the writer; over-aggressive ignore tags after refactoring; structs relying solely on fields the generator skips.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• unsupported type: %v
• can't load rules: %v
• not found
• required field is missing
• expected struct, got %v

AI-assisted analysis of cayleygraph/cayley@81dcd7d73e (2026-09-06). Data as JSON: /api/errors/c25aaf9206f6a6c3. Report an issue: GitHub.