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ScopeEnumMismatchError

Symptom

container.validate() raises ValidationFailedError, and one of its .exceptions is a ScopeEnumMismatchError:

  + Exception Group Traceback (most recent call last):
  |   ...
  | modern_di.exceptions.container.ValidationFailedError: Container.validate() found 1 issue(s): ScopeEnumMismatchError (1)
  | See: https://modern-di.modern-python.org/troubleshooting/validation-failed-error/
  +-+---------------- 1 ----------------
    | modern_di.exceptions.registration.ScopeEnumMismatchError: Provider at a same-valued scope of another enum reached through this chain:
    |   SESSION  UserSession (myapp.providers:13)
    |   TENANT   └─> TenantSettings (myapp.providers:10)
    |   caused by: UserSession (scope Scope.SESSION) declares parameter 'settings' typed as a provider of TenantSettings at scope Tenancy.TENANT. Both scopes have the value 2 but belong to different enums, so they can never be in one container chain. Give the dependency the same scope member as UserSession or a shallower one.
    | See: https://modern-di.modern-python.org/troubleshooting/scope-enum-mismatch-error/
    +------------------------------------

Inspect .provider, .parameter_name and .dependency_chain on the exception. .dependency_provider and .dependency_terminal are the ends of the chain; they differ when the dependency is reached through an Alias.

Cause

A provider matches its container by enum member. Scopes from different enums can share a value, like Scope.SESSION and Tenancy.TENANT here, which are both 2. A container chain holds at most one container per value, because each child's value is higher than its parent's. The SESSION container is the one at value 2, so no TENANT container can exist in its chain, and UserSession can never resolve its settings dependency. Resolving it without validate() raises ScopeSkippedError.

A dependency on a shallower scope from another enum is fine. A Scope.REQUEST provider can depend on a Tenancy.TENANT provider when the chain is built APP → TENANT → REQUEST.

Fix

Give the dependency the same scope member as the provider that needs it, or a shallower one:

class Tenancy(IntEnum):
    TENANT = 2


# Broken: TENANT and SESSION are both 2
class BrokenDependencies(Group):
    settings = providers.Factory(TenantSettings, scope=Tenancy.TENANT)
    session = providers.Factory(UserSession, scope=Scope.SESSION)


Container(groups=[BrokenDependencies]).validate()

# Works: the dependency is shallower than the provider
class Dependencies(Group):
    settings = providers.Factory(TenantSettings, scope=Scope.APP)
    session = providers.Factory(UserSession, scope=Scope.SESSION)


Container(groups=[Dependencies]).validate()

See also