hasura/graphql-engine · error · StringOperatorReason

argument type '{argument_type}' is not a string

Error message

argument type '{argument_type}' is not a string

What it means

Nested reason for OnlyApplicableOnStringScalar: the operator's argument type is not a string type.

Source

Thrown at v3/crates/metadata-resolve/src/stages/scalar_boolean_expressions/error.rs:183

    )]
    OnlyApplicableOnStringScalar {
        type_name: Qualified<CustomTypeName>,
        operator_name: OperatorName,
        reason: StringOperatorReason,
    },
}

impl ShouldBeAnError for ScalarBooleanExpressionOperatorIssue {
    fn should_be_an_error(&self, flags: &flags::OpenDdFlags) -> bool {
        flags.contains(flags::Flag::ValidateScalarBooleanExpressionOperators)
    }
}

#[derive(Debug, thiserror::Error)]
pub enum StringOperatorReason {
    #[error("scalar type '{scalar_type}' is not a string")]
    ScalarTypeNotString { scalar_type: QualifiedTypeName },
    #[error("argument type '{argument_type}' is not a string")]
    ArgumentTypeNotString { argument_type: QualifiedTypeName },
    #[error("argument type '{argument_type}' is a list")]
    ArgumentTypeShouldNotBeList {
        argument_type: QualifiedTypeReference,
    },
}

#[derive(Debug, Eq, PartialEq, Copy, Clone, derive_more::with_trait::Display)]
#[allow(clippy::enum_variant_names)] // It's fine that they all end with "Operator" :/
pub enum FieldNameSource {
    #[display("comparable operator")]
    ComparisonOperator,
    #[display("logical operator")]
    LogicalOperator,
    #[display("is null operator")]
    IsNullOperator,
}

View on GitHub (pinned to 724551b9ae)

Solutions

1. Change the operator's argument type to the string scalar the boolean expression is defined on

Example fix

// before
argument_type: {scalar: Numeric}
// after
argument_type: {scalar: String}

fn argument_is_string(t: &QualifiedTypeName) -> bool {
    matches!(t, QualifiedTypeName::BuiltIn(open_dds::types::BuiltInType::String))
}

When it happens

Trigger: A string operator's argument uses a non-string QualifiedTypeName (e.g. numeric or uuid).

Common situations: Mismatched argument type when hand-authoring string operators.

Related errors

• the operator '{operator_name}' in the boolean expression '{t
• scalar type '{scalar_type}' is not a string
• argument type '{argument_type}' is a list
• the operand type '{operand_type}' does not match the operand
• type mismatch between the aggregation function '{aggregation

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/dabfd750266d127b. Report an issue: GitHub.