hasura/graphql-engine · error · AggregateBooleanExpressionError

the comparable relationship '{relationship_name}' for the op

Error message

the comparable relationship '{relationship_name}' for the operand type '{operand_type}' is an array relationship. This is not supported

What it means

Comparable relationships must be object (single) relationships; array relationships are rejected because nested aggregate boolean expressions over array relationships are not supported by this stage.

Source

Thrown at v3/crates/metadata-resolve/src/stages/aggregate_boolean_expressions/types.rs:311

    },

    #[error(
        "the comparable relationship '{relationship_name}' was not found for the operand type '{operand_type}'"
    )]
    ComparableRelationshipNotFound {
        operand_type: Qualified<CustomTypeName>,
        relationship_name: RelationshipName,
    },

    #[error(
        "the comparable relationship '{relationship_name}' for the operand type '{operand_type}' targets a command. This is not supported"
    )]
    ComparableRelationshipCommandTargetNotSupported {
        operand_type: Qualified<CustomTypeName>,
        relationship_name: RelationshipName,
    },

    #[error(
        "the comparable relationship '{relationship_name}' for the operand type '{operand_type}' is an array relationship. This is not supported"
    )]
    ComparableArrayRelationshipNotSupported {
        operand_type: Qualified<CustomTypeName>,
        relationship_name: RelationshipName,
    },

    #[error(
        "the comparable relationship '{relationship_name}' for the operand type '{operand_type}' targets a model than cannot be found: '{target_model_name}'"
    )]
    ComparableRelationshipTargetModelNotFound {
        operand_type: Qualified<CustomTypeName>,
        relationship_name: open_dds::relationships::RelationshipName,
        target_model_name: Qualified<open_dds::models::ModelName>,
    },

    #[error(
        "the comparable relationship '{relationship_name}' for the operand type '{operand_type}' references a boolean expression type that cannot be found: '{boolean_expression_type}'"

View on GitHub (pinned to 724551b9ae)

Solutions

1. Remove the array relationship from comparableRelationships
2. Restructure the metadata so aggregation goes through an object relationship to a type that models the child collection
3. Filter on the child side or via a dedicated aggregate model/relationship instead

Example fix

# before
# Author --articles--> [Article] (array relationship)
comparableRelationships:
  - relationshipName: articles

# after
comparableRelationships:
  - relationshipName: profile   # object relationship only
# query aggregates on Article directly: article_aggregate(where: {rating: {_gt: 4}})

for r in &comparable_relationships {
    let rel = operand_type.relationships[&r.relationship_name];
    assert!(!rel.is_array(), "array relationship cannot be comparable");
}

When it happens

Trigger: Marking an array (many) relationship as a comparable relationship for aggregate boolean expressions.

Common situations: Trying to filter parents by aggregates of their children (e.g. authors where their articles' avg rating > x) by marking the articles array relationship as comparable, which this feature does not support; misunderstanding which relationship kinds allow nested aggregation.

Related errors

• the type of the comparable field '{field_name}' ({field_type
• the boolean expression type ({boolean_expression_type}) used
• the comparable relationship '{relationship_name}' for the op
• Condition {condition_hash} not found
• could not find a scalar-operanded boolean expression type na

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/3db710804ddbc265. Report an issue: GitHub.