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

Ensure sqrt's argument is an int/float predicate or numeric variable

Wrong type %v encountered for func sqrt

Error message

Wrong type %v encountered for func sqrt

What it means

The `sqrt` unary function computes the square root only for INT, FLOAT, and BIGFLOAT values (BIGFLOAT handled with big.Float at configured precision). If the operand type is anything else, the DEFAULT branch of the type switch returns this error with the offending type ID.

Source

Thrown at query/aggregator.go:521

		if a.Value.(int64) < 0 {
			return ErrorNegativeRoot
		}
		res.Value = math.Sqrt(float64(a.Value.(int64)))
		res.Tid = types.FloatID

	case FLOAT:
		if a.Value.(float64) < 0 {
			return ErrorNegativeRoot
		}
		res.Value = math.Sqrt(a.Value.(float64))

	case BIGFLOAT:
		value := a.Value.(big.Float)
		rt := big.NewFloat(0).SetPrec(types.BigFloatPrecision).Sqrt(&value)
		res.Value = *rt

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

func applyFloor(a, res *types.Val) error {
	vBase := getValType(a)
	switch vBase {
	case INT:
		res.Value = a.Value.(int64)

	case FLOAT:
		res.Value = math.Floor(a.Value.(float64))

	case BIGFLOAT:
		value := a.Value.(big.Float)
		f, _ := value.Float64()
		res.Value = *big.NewFloat(math.Floor(f)).SetPrec(types.BigFloatPrecision)

View on GitHub (pinned to 759e242be6)

Solutions

Ensure sqrt's argument is an int/float predicate or numeric variable
Check the schema to confirm the predicate's type
Filter or coerce the value to numeric before sqrt
Validate the expression with a literal argument to confirm the rest of the query works

Example fix

// before
"math sqrt(distance_str)"
// after
"math sqrt(distance)"

Defensive patterns

Strategy: type-guard

Validate before calling

const t = schemaOf('distance');
if (t !== 'float' && t !== 'int') throw new Error('sqrt needs numeric type');

Type guard

function isSqrtSafe(v) { return typeof v === 'number' && v >= 0; }

Try / catch

try {
  out = await txn.query(q);
} catch (e) {
  if (String(e).includes('func sqrt')) throw new TypeError('sqrt operand must be numeric');
  throw e;
}

Prevention

Use sqrt only on int/float predicates
Verify operand types in generated queries
Keep schema and query in sync after migrations
Guard against negative inputs at query design time

When it happens

Trigger: A query math sqrt(x) where x is a non-numeric value: string/bool/dateTime predicate or a default-typed variable.

Common situations: sqrt over a string predicate; variable shadows a uid; predicate resharded or schema changed so values no longer arrive as float; facet values that are strings.

Related errors

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/a6e2b21fabff98d5. Report an issue: GitHub.