Duplicate Type Error

This error occurs when two or more providers are registered with the same bound_type. Modern-DI uses the bound_type to resolve dependencies by type, so each type must be unique in the providers registry.

Understanding the Error

When you see this error:

RuntimeError: Provider is duplicated by type <class 'SomeType'>.

It means you have multiple providers that can provide the same type. This typically happens when:

1. You have multiple factories that return the same type
2. You're using the same class in different contexts with different configurations

How to Resolve

To fix this error, you need to:

1. Set bound_type=None on one of the duplicate providers to make it unresolvable by type
2. Explicitly pass dependencies via the kwargs parameter to avoid automatic resolution

Here's a complete example showing both steps:

from modern_di import Group, Scope, providers


class DatabaseConfig:
    def __init__(self, connection_string: str) -> None:
        self.connection_string = connection_string


class Repository:
    def __init__(self, db_config: DatabaseConfig) -> None:
        self.db_config = db_config


class MyGroup(Group):
    # Step 1: Set bound_type=None on the secondary provider or for both providers
    # This provider can be resolved by type: container.resolve(DatabaseConfig)
    primary_db_config = providers.Factory(
        scope=Scope.APP,
        creator=DatabaseConfig,
        kwargs={"connection_string": "postgresql://primary"}
    )

    # This provider cannot be resolved by type
    # Must use: container.resolve_provider(MyGroup.secondary_db_config)
    secondary_db_config = providers.Factory(
        scope=Scope.APP,
        creator=DatabaseConfig,
        bound_type=None,  # <-- Step 1: Makes it unresolvable by type
        kwargs={"connection_string": "postgresql://secondary"}
    )

    # Step 2: Explicitly pass dependencies via kwargs for second repository or for both
    primary_repository = providers.Factory(
        scope=Scope.APP,
        creator=Repository,  # <-- Implicit dependency, no kwargs
    )

    secondary_repository = providers.Factory(
        scope=Scope.APP,
        creator=Repository,
        kwargs={"db_config": secondary_db_config}  # <-- Step 2: Explicit dependency
    )