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Errors

This page describes errors and custom exceptions raised by Rodi.

Errors

Name Description
CannotResolveTypeException This error is raised when a type cannot be resolved because it was not registered in the container.
CircularDependencyException This error is raised when a circular dependency is detected and cannot be resolved.
FactoryMissingContextException This error is raised when a factory function does not have _locals. This generally happens only if classes are defined inside functions and use locals (not a common case).
MissingTypeException This error is raised when a factory function does not specify its return type annotation, and the user does not specify the type it returns.
OverridingServiceException This error is raised when the user tries to override a type that is already registered in the container.

Cannot resolve type

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from rodi import Container


class A: ...

class B:
    dependency: A


container = Container()
container.register(B)

container.resolve(B)  # <-- raises exception 💥

rodi.CannotResolveParameterException: Unable to resolve parameter 'dependency' when resolving 'B'

All dependencies must be explicitly registered in the container. To resolve the error, register the missing type:

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from rodi import Container


class A: ...

class B:
    dependency: A


container = Container()
container.register(A)
container.register(B)

container.resolve(B)

The chicken and egg problem 🐔 🥚

The following classes have a circular dependency:

class Chicken:
    egg: "Egg"


class Egg:
    chicken: Chicken

If we try to have Rodi resolve them automatically, we get an error:

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from rodi import Container


class Chicken:
    egg: "Egg"


class Egg:
    chicken: Chicken


container = Container()
container.register(Chicken)
container.register(Egg)

# The following line raises an exception:
chicken = container.resolve(Chicken)  # 💥

The raised error is:

raise CircularDependencyException(chain[0], concrete_type) rodi.CircularDependencyException: A circular dependency was detected for the service of type 'Chicken' for 'Egg'.

Rodi cannot infer automatically which type should be instantiated first: Chicken or Egg?

Last modified on: 2025-04-17 07:04:37

RP