dgraph-io/dgraph · error

can't convert input.what to string

Error message

can't convert input.what to string

What it means

getAssignInput reads input.what from the assign mutation input and requires it to be a string (the kind of value to assign, e.g. "uids"). A missing or non-string 'what' key produces this inputArgError.

Source

Thrown at graphql/admin/assign.go:86

				"startId":  startId,
				"endId":    endId,
				"readOnly": readOnly,
			},
		}},
		nil,
	), true
}

func getAssignInput(m schema.Mutation) (*assignInput, error) {
	inputArg, ok := m.ArgValue(schema.InputArgName).(map[string]interface{})
	if !ok {
		return nil, inputArgError(errors.Errorf("can't convert input to map"))
	}

	inputRef := &assignInput{}
	inputRef.What, ok = inputArg["what"].(string)
	if !ok {
		return nil, inputArgError(errors.Errorf("can't convert input.what to string"))
	}

	num, err := parseAsUint64(inputArg["num"])
	if err != nil {
		return nil, inputArgError(schema.GQLWrapf(err, "can't convert input.num to uint64"))
	}
	inputRef.Num = num

	return inputRef, nil
}

View on GitHub (pinned to 759e242be6)

Solutions

1. Add or fix input.what as a string, e.g. {"what": "uids", "num": 100}.
2. Check the mutation schema (assignDgraphMutation input type) for the exact field name and type.
3. Validate the payload JSON before sending.

Example fix

// before
{"what": 3, "num": 100}
// after
{"what": "uids", "num": 100}

function requireAssignWhat(input) {
  if (typeof input?.what !== 'string') throw new Error("input.what must be a string, e.g. 'uids'");
}

function hasStringWhat(v) { return typeof v === 'object' && v !== null && typeof v.what === 'string' && v.what.length > 0; }

try { await assign(input); } catch (e) { if (String(e).includes("can't convert input.what to string")) { throw new Error('Missing or non-string input.what in assign mutation'); } throw e; }

When it happens

Trigger: assignDgraphMutation input object without a 'what' field, or with a non-string value (number, object, enum passed as non-string) at graphql/admin/assign.go:86.

Common situations: Omitting 'what' in hand-written payloads; confusing the enum-like value and sending an integer; older clients using a removed field name (e.g. 'type') instead of 'what'.

Related errors

• can't convert input to map
• can't convert input to map
• can't convert input to map
• not able to find set args in update mutation
• you must specify a 'destination' value

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/56f090ffc006c11d. Report an issue: GitHub.