apache/cassandra · error · InvalidRequestException

Function %s requires a %s vector argument, but found argumen

Error message

Function %s requires a %s vector argument, but found argument %s of type %s

What it means

Functions accepting vector arguments validate that the argument is a ListType whose element type is assignable to the expected vector element type. validateType() throws this InvalidRequestException when the argument is not such a list (wrong container type or wrong element type). It means a vector (list) argument of the required element type was expected.

Source

Thrown at src/java/org/apache/cassandra/cql3/functions/FunctionParameter.java:392

            }

            @Override
            public void validateType(FunctionName name, AssignmentTestable arg, AbstractType<?> argType)
            {
                if (argType.isVector())
                {
                    VectorType<?> vectorType = (VectorType<?>) argType;
                    if (vectorType.elementType.asCQL3Type() == type)
                        return;
                }
                else if (argType instanceof ListType) // if it's terminal it will be a list
                {
                    ListType<?> listType = (ListType<?>) argType;
                    if (listType.getElementsType().testAssignment(type.getType()) == NOT_ASSIGNABLE)
                        return;
                }

                throw new InvalidRequestException(format("Function %s requires a %s vector argument, " +
                                                         "but found argument %s of type %s",
                                                         name, type, arg, argType.asCQL3Type()));
            }

            @Override
            public String toString()
            {
                return format("vector<%s, n>", type);
            }
        };
    }
}

View on GitHub (pinned to 88fd0f6a0e)

Solutions

  1. Pass a list literal with the correct element type, e.g. [1.0, 2.0, 3.0] for vector<float>.
  2. Verify the column/argument type matches the expected vector element type; recreate/ALTER if it drifted.
  3. Check the function's signature (FunctionFactory description) for the exact expected vector type.
  4. Cast via a UDF if a conversion is genuinely needed.

Example fix

// before
SELECT similarity(vec, ['a','b']) FROM t; -- vector<text> passed
// after
SELECT similarity(vec, [1.0, 2.0]) FROM t; -- vector<float> passed
Defensive patterns

Strategy: type-guard

Validate before calling

if (!(t instanceof ListType)) throw new IllegalArgumentException("vector arg must be a list");
ListType<?> lt = (ListType<?>) t;
if (lt.getElementsType().testAssignment(expectedElementType) == AssignmentTestable.Result.NOT_ASSIGNABLE)
    throw new IllegalArgumentException("element type " + lt.getElementsType().asCQL3Type() + " not assignable");

Type guard

boolean isVectorArg(AbstractType<?> t, AbstractType<?> elem) { return t instanceof ListType && ((ListType<?>) t).getElementsType().testAssignment(elem) != AssignmentTestable.Result.NOT_ASSIGNABLE; }

Try / catch

try { session.execute(q); } catch (InvalidRequestException e) { if (e.getMessage().contains("vector argument")) { /* supply list with correct element type */ } else throw e; }

Prevention

When it happens

Trigger: Calling a vector-parameter function (e.g. vector similarity/format functions) with a non-list type, or a list whose element type does not match the expected float/vector element type (testAssignment == NOT_ASSIGNABLE).

Common situations: Passing a vector<string> where vector<float> is required; passing a single scalar instead of a list; schema drift where the column's element type changed.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/686fa7521bc3ff38. Report an issue: GitHub.