hasura/graphql-engine · error · TypePredicateError::TypeMappingCollectionError

{error:} in type {type_name:}

Error message

{error:} in type {type_name:}

What it means

Wrapper error attaching the type name to a TypeMappingCollectionError raised while collecting the type mappings for that type. The inner `error` (a TypeMappingCollectionError) describes the concrete problem — e.g. duplicate or conflicting type mappings — and this variant tells you which type it happened on.

Source

Thrown at v3/crates/metadata-resolve/src/types/error.rs:511

        relationship_name: Spanned<RelationshipName>,
        boolean_expression_type_name: Qualified<CustomTypeName>,
    },
    #[error(
        "The model '{target_model_name:}' corresponding to the  relationship '{relationship_name:}' used in predicate for type '{type_name:}' is not defined"
    )]
    UnknownModelUsedInRelationshipTypePredicate {
        type_name: Qualified<CustomTypeName>,
        target_model_name: Qualified<ModelName>,
        relationship_name: RelationshipName,
    },
    #[error(
        "target source for model '{target_model_name:}' is required to resolve predicate with relationships for {source_type_name:}"
    )]
    TargetSourceRequiredForRelationshipPredicate {
        source_type_name: Qualified<CustomTypeName>,
        target_model_name: Qualified<ModelName>,
    },
    #[error("{error:} in type {type_name:}")]
    TypeMappingCollectionError {
        type_name: Qualified<CustomTypeName>,
        error: TypeMappingCollectionError,
    },
    #[error("expected object type for field {field_name:} but field had type {field_type:}")]
    ExpectedObjectType {
        field_type: QualifiedTypeReference,
        field_name: Spanned<FieldName>,
    },
    #[error("object type {type_name:} not found")]
    ObjectTypeNotFound {
        type_name: Qualified<CustomTypeName>,
    },
    #[error("operator mappings not found for data connector {data_connector_name:}")]
    OperatorMappingsNotFound {
        data_connector_name: Qualified<DataConnectorName>,
    },
    #[error("no type mapping found for type {type_name:} in data connector {data_connector_name:}")]

View on GitHub (pinned to 724551b9ae)

Solutions

1. Read the inner `{error}` message — it carries the specific TypeMappingCollectionError (e.g. duplicate mapping details)
2. Fix the reported mapping conflict on `type_name` (remove the duplicate or reconcile the two representations)
3. Re-run metadata resolve to confirm the collection step now succeeds
4. Add CI metadata validation to catch mapping conflicts before deploy

Example fix

# before: same underlying type mapped twice with different representations
# TypeMappingCollectionError: duplicate mapping ...
# after: keep a single consistent representation
fields:
  a: {type: string, mapping: {column: a}}
  b: {type: string, mapping: {column: b}}

// Pre-flight: detect duplicate/conflicting type mappings before resolution
let mut seen = HashSet::new();
for m in collect_mappings(&type_mappings) {
    if !seen.insert(m.type_name.clone()) {
        return Err(format!("duplicate mapping for {}", m.type_name));
    }
}
Ok(())

if let Err(TypePredicateError::TypeMappingCollectionError { type_name, error }) = result {
    return Err(format!("mapping error on {type_name}: {error}"));
}

When it happens

Trigger: A type's mapping collection (the per-type aggregation of field type mappings into the NDC schema) fails — commonly duplicate type mappings for the same type, or conflicting representations collected while building the type's schema.

Common situations: Two fields mapping to the same underlying type with different representations; copy-pasted type mappings creating duplicates; connector schema generation hitting inconsistent mappings after metadata merges.

Related errors

• the type {unknown_ndc_type:} is not defined as an object typ
• field '{field_name}' of type '{type_name}' used in a field c
• metadata is not consistent: {error}
• An issue occurred while mapping arguments in the model {mode
• the type {unknown_ndc_field_type_name:} is not defined as an

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/8a4ded73e8d0f91a. Report an issue: GitHub.