cayleygraph/cayley · error

can't load rules: %v

Error message

can't load rules: %v

What it means

writeAsQuads asks the Config for conversion rules via rulesFor(rt), which runs full schema generation for the struct type. Any error during generation (bad tags, unsupported fields, anonymous fields) is wrapped as "can't load rules". The root cause is always an inner schema-generation failure reported in the wrapped message.

Source

Thrown at schema/writer.go:160

		return quad.String(rv.String()), nil
	} else if kind == reflect.Int || kind == reflect.Uint ||
		kind == reflect.Int32 || kind == reflect.Uint32 ||
		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
	}

View on GitHub (pinned to 81dcd7d73e)

Solutions

1. Read the wrapped inner error to find the exact offending field/rule
2. Call Generate once at startup for all schema structs so errors surface early
3. Fix the invalid struct tag or unsupported field identified in the wrapped message

Example fix

// before
type Doc struct {
    Fn func() `tag:"fn"`
}
// after
type Doc struct {
    Name string `tag:"name"`
}

if err := schema.Generate(cfg, Doc{}); err != nil {
    return fmt.Errorf("schema invalid before write: %w", err)
}

if _, err := w.WriteAsQuads(qs, doc); err != nil {
    var wrapped string = err.Error()
    if strings.Contains(wrapped, "can't load rules") {
        log.Printf("fix struct schema: %v", wrapped) // inner cause included
        return err
    }
    return err
}

When it happens

Trigger: Writing a struct whose schema generation fails - e.g. a func-typed field, unsupported embedded field, or a malformed quad-format tag string.

Common situations: First write of a newly added struct with invalid `tag:"..."` annotations; refactoring a struct to add callbacks or embedded primitives then writing it.

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

• wrong quad format: '%s': no predicate
• unsupported type: %v
• no rules for struct: %v
• HTTP Request needed
• ErrEmptyPath

AI-assisted analysis of cayleygraph/cayley@81dcd7d73e (2026-09-06). Data as JSON: /api/errors/90d0377453a3633e. Report an issue: GitHub.