hasura/graphql-engine · error · TypeError::TypeCheckError

type mismatch: {error:}

Error message

type mismatch: {error:}

What it means

A TypeError wrapper indicating that a value expression failed type checking: the expression's inferred type did not match the type expected by its context (argument, field, comparison, etc.). The underlying TypecheckError carries specifics of the mismatch (e.g. string vs uuid).

Source

Thrown at v3/crates/metadata-resolve/src/types/error.rs:715

                        path: field_name.path.clone(),
                        subgraph: field_type.get_subgraph().cloned(),
                    }
                ))
            }

            TypePredicateError::ScalarBooleanExpressionTypeError(error) => error.create_error_context(),
            _ => None
        }
    }
}

#[derive(Debug, thiserror::Error)]
pub enum TypeError {
    #[error("expected to find a custom named type in {qualified_type_reference:} but none found")]
    NoNamedTypeFound {
        qualified_type_reference: QualifiedTypeReference,
    },
    #[error("type mismatch: {error:}")]
    TypeCheckError { error: TypecheckError },
}

impl From<AggregateExpressionError> for Error {
    fn from(val: AggregateExpressionError) -> Self {
        Error::AggregateExpressionError(val)
    }
}

impl From<TypecheckError> for Error {
    fn from(type_error: TypecheckError) -> Self {
        Error::TypeError {
            type_error: TypeError::TypeCheckError { error: type_error },
        }
    }
}

View on GitHub (pinned to 724551b9ae)

Solutions

1. Read the inner TypecheckError message for expected vs actual types
2. Fix the expression (literal, preset, or variable) so its type matches the declared argument/field type
3. If a session variable is involved, remember it is a string; cast or compare accordingly

Example fix

// before
preset: "2023-01-01" // declared as date comparison
// after
preset: { eq: "2023-01-01" } // matches the comparison type

// Validate expression types against the declared argument type before submission
assert_expression_type_matches(&expr, &declared_type)?;

match result {
    Err(Error::TypeError(TypeError::TypeCheckError { error })) => {
        eprintln!("type mismatch: {error}");
    }
    _ => {}
}

When it happens

Trigger: Any metadata resolution path that runs the typechecker on expressions, e.g. argument presets, command arguments, or filter expressions where the expression type (literal, variable, session variable) does not unify with the declared target type (TypeCheckError { error: TypecheckError }).

Common situations: Passing a string literal or session variable where a uuid/date/comparison type is declared; boolean expressions used where a scalar is expected; mismatches after changing a field's type without updating presets.

Related errors

• error fetching config from server: %w
• error fetching server config: %v
• cannot write metadata directory: %w
• cannot create metadata files: %w
• got error while getting the sources list : %w

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/4314aa3d6cc99c2b. Report an issue: GitHub.