hasura/graphql-engine · error · AggregateBooleanExpressionError

the operand type '{operand_type}' must be an object type

Error message

the operand type '{operand_type}' must be an object type

What it means

AggregateBooleanExpressionError::OperandTypeIsNotAnObjectType: the aggregate boolean expression's operand must be an object type in this position, but the declared operand type resolves to something else (e.g. a scalar). The message includes the offending operand type.

Source

Thrown at v3/crates/metadata-resolve/src/stages/aggregate_boolean_expressions/types.rs:142

}

#[derive(Debug, thiserror::Error)]
pub enum AggregateBooleanExpressionError {
    #[error("boolean expressions with aggregate operands are not supported")]
    AggregateBooleanExpressionsNotSupported,

    #[error("boolean expressions with aggregate operands do not support isNull comparisons")]
    IsNullComparisonsNotSupported,

    #[error("{0}")]
    GraphqlConfigError(#[from] GraphqlConfigError),

    #[error("the operand type '{operand_type}' must be a scalar type")]
    OperandTypeIsNotAScalarType {
        operand_type: Qualified<CustomTypeName>,
    },

    #[error("the operand type '{operand_type}' must be an object type")]
    OperandTypeIsNotAnObjectType {
        operand_type: Qualified<CustomTypeName>,
    },

    #[error("the aggregate expression '{aggregate_expression}' could not be found")]
    AggregateExpressionNotFound {
        aggregate_expression: Qualified<AggregateExpressionName>,
    },

    #[error(
        "the operand type '{operand_type}' does not match the operand type '{aggregate_operand}' from the aggregate expression '{aggregate_expression}'"
    )]
    AggregateOperandTypeMismatch {
        operand_type: QualifiedTypeName,
        aggregate_expression: Qualified<AggregateExpressionName>,
        aggregate_operand: QualifiedTypeName,
    },

View on GitHub (pinned to 724551b9ae)

Solutions

  1. Set the operand type to the object type being filtered
  2. Verify the object type exists in the same subgraph and is spelled correctly
  3. Re-read the aggregate boolean expression definition to confirm operand roles

Example fix

# before
operand:
  type: app.UserStatus   # scalar

# after
operand:
  type: app.User   # object type
Defensive patterns

Strategy: validation

Validate before calling

fn operand_is_object(metadata: &Metadata, operand: &Qualified<CustomTypeName>) -> bool {
    metadata.object_types.contains_key(operand)
}

Try / catch

if let AggregateBooleanExpressionError::OperandTypeIsNotAnObjectType { operand_type } = err {
    eprintln!("{operand_type:?} must be declared as an object type");
}

Prevention

When it happens

Trigger: Declaring the target operand of an aggregate boolean expression with a scalar type where the definition requires an object type (the type whose fields are being aggregated/compared).

Common situations: Pointing the operand at a scalar by mistake, renaming types so the operand now resolves to a scalar, misunderstanding which side of the expression must be the object type.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/fbff53e60c778a9b. Report an issue: GitHub.