What causes "Wrong type %v encountered for func +" in dgraph-io/dgraph?

Declare a concrete scalar type (int/float) in the schema for predicates used in math

Wrong type %v encountered for func +

Error message

Wrong type %v encountered for func +

What it means

applyAdd returns this error when an addition (+) operand has DEFAULT type, i.e. the value's type id is unset or unsupported for arithmetic. Dgraph only adds int/float/bigfloat typed values; a DEFAULT-typed operand indicates missing or untyped data reaching the math evaluator.

Source

Thrown at query/aggregator.go:145

		if !ok {
			return ErrorArgsDisagree
		}
		if len(aVal) != len(bVal) {
			return ErrorVectorsNotMatch
		}
		cVal := make([]float32, len(aVal))
		for i := range aVal {
			cVal[i] = aVal[i] + bVal[i]
		}
		c.Value = cVal

	case BIGFLOAT:
		aVal, bVal := a.Value.(big.Float), b.Value.(big.Float)
		aVal.Add(&aVal, &bVal)
		c.Value = aVal

	case DEFAULT:
		return errors.Errorf("Wrong type %v encountered for func +", a.Tid)
	}
	return nil
}

func applySub(a, b, c *types.Val) error {
	vBase := getValType(a)
	switch vBase {
	case INT:
		aVal, bVal := a.Value.(int64), b.Value.(int64)
		if (bVal < 0 && aVal > math.MaxInt64+bVal) ||
			(bVal > 0 && aVal < math.MinInt64+bVal) {
			return ErrorIntOverflow
		}
		c.Value = aVal - bVal

	case FLOAT:
		c.Value = a.Value.(float64) - b.Value.(float64)
	case VFLOAT:

View on GitHub (pinned to 759e242be6)

Solutions

Declare a concrete scalar type (int/float) in the schema for predicates used in math
Coerce operands explicitly with math functions (e.g. math(val) via typed vars) before +
Filter out nodes where the value is missing before applying arithmetic

Example fix

// before
math(a + b) // a untyped/DEFAULT
// after: ensure schema: a: int .
// or coerce: math(int(a) + b) only after validating a is numeric

Defensive patterns

Strategy: validation

Validate before calling

func isNumericVal(v types.Val) bool {
    t := getValType(&v)
    return t == INT || t == FLOAT || t == BIGFLOAT
}

Type guard

func isAddable(a, b types.Val) bool {
    return isNumericVal(a) && isNumericVal(b)
}

Try / catch

if err := applyAdd(a, b, c); err != nil {
    if strings.Contains(err.Error(), "func +") {
        return fmt.Errorf("operand type %v not supported for +; declare predicate as int/float", a.Tid)
    }
    return err
}

Prevention

Declare scalar schema types for all predicates used in math()
Coerce with int()/float() math functions when types may vary
Filter out nodes with missing values before arithmetic
Check that fetched values are not uid or empty before math

When it happens

Trigger: A math expression like math("+", a, b) evaluates where one operand resolved to DEFAULT type — e.g. the predicate had no schema type, the value was empty/uid, or conversion earlier in the pipeline left the type unset.

Common situations: Math functions applied to predicates without a declared scalar type; operations on empty optional values; summing over values fetched from an untyped or uid predicate.

Related errors

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/9c98e65ce01d0f8b. Report an issue: GitHub.