hasura/graphql-engine · error · TypeMappingCollectionError

No support for using the same type {type_name:} against mult

Error message

No support for using the same type {type_name:} against multiple data connector objects {ndc_type_1:} and {ndc_type_2:}

What it means

The same custom type is mapped to two different NDC object types, which is unsupported. Type mapping collection enforces one-to-one mapping between a custom type and a data connector object type.

Source

Thrown at v3/crates/metadata-resolve/src/helpers/type_mappings.rs:27

use std::collections::BTreeMap;

#[derive(Debug)]
pub struct TypeMappingToCollect<'a> {
    pub type_name: &'a Qualified<CustomTypeName>,
    pub ndc_object_type_name: &'a ndc_models::TypeName,
}

#[derive(thiserror::Error, Debug)]
pub enum TypeMappingCollectionError {
    #[error(
        "No mapping defined for type {type_name:} to object {ndc_type_name:} of data connector {data_connector:}"
    )]
    MappingNotDefined {
        type_name: Qualified<CustomTypeName>,
        data_connector: Qualified<DataConnectorName>,
        ndc_type_name: DataConnectorObjectType,
    },
    #[error(
        "No support for using the same type {type_name:} against multiple data connector objects {ndc_type_1:} and {ndc_type_2:}"
    )]
    MappingToMultipleDataConnectorObjectType {
        type_name: Qualified<CustomTypeName>,
        ndc_type_1: DataConnectorObjectType,
        ndc_type_2: DataConnectorObjectType,
    },
    #[error(
        "Missing mapping for field {field_name:} when mapping type {type_name:} to object {ndc_type_name:} of data connector {data_connector:}"
    )]
    MissingFieldMapping {
        type_name: Qualified<CustomTypeName>,
        field_name: FieldName,
        data_connector: Qualified<DataConnectorName>,
        ndc_type_name: DataConnectorObjectType,
    },

    #[error("Cannot return a predicate type from a command")]

View on GitHub (pinned to 724551b9ae)

Solutions

1. Remove or consolidate duplicate mappings so the type maps to exactly one NDC object type
2. If two shapes are genuinely needed, create two distinct custom types and map each separately
3. Audit all typeMappings blocks referencing the type

let mut seen: HashMap<Type, Object> = HashMap::new();
assert!(!seen.insert(ty, obj).is_some()); // dedupe before resolve

When it happens

Trigger: Defining mappings for type T to object A on one model/link and to object B on another; duplicate mapping entries with different ndc object type names.

Common situations: Copy-pasting mappings across subgraphs or connectors; refactoring that leaves stale mappings; merging metadata branches that both add mappings.

Related errors

• the type {unknown_ndc_type:} is not defined as an object typ
• mapping for type {type_name} of model {model_name} is not de
• mapping for type {type_name} of command {command_name} is no
• No mapping defined for type {type_name:} to object {ndc_type
• Missing mapping for field {field_name:} when mapping type {t

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/c5c12504120b71c5. Report an issue: GitHub.