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update decoupled-example with abstraction layer #770

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fanqingsong
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Hi
The decoupled-example code is good, but it lack one important component of DIP rule (https://www.cs.utexas.edu/users/downing/papers/DIP-1996.pdf)
I mean the "Abstraction" layer which can help make "user" and "photo" compliant to abstract classes of their own and "analytics" depends on these abstract classes, and even for "analytics" can be extracted one abstract class, then for main.py (the top-level service aggregation) can only depend on these three abstract class, finally "ApplicationContainer" is for connecting the embodied containers("user", "photo", "analytics") to main.py.
The update code is better to demostrate DIP rule for developer.

I also update docs part.

Please check.
Thanks.

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This PR needs some addition work.

from ..user.repositories import UserRepositoryMeta


class AggregationServiceMeta(metaclass=abc.ABCMeta):
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Suggested change
class AggregationServiceMeta(metaclass=abc.ABCMeta):
class AggregationService(metaclass=abc.ABCMeta):

Meta suffix might give it a wrong impression that this is a metaclass. Let's avoid ambiguous naming.

self.user_repository = user_repository
self.photo_repository = photo_repository

class AggregationService(AggregationServiceMeta):
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Suggested change
class AggregationService(AggregationServiceMeta):
class AggregationServiceImpl(AggregationService):

or

Suggested change
class AggregationService(AggregationServiceMeta):
class MemoryAggregationService(AggregationService):

See comment above. This way it would be much more clear about implementation specifics of the AggregationService interface.

Comment on lines +12 to +14
def __init__(self, user_repository: UserRepositoryMeta, photo_repository: PhotoRepositoryMeta):
self.user_repository: UserRepositoryMeta = user_repository
self.photo_repository: PhotoRepositoryMeta = photo_repository
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Interfaces generally has no __init__, it's an implementation detail.

Suggested change
def __init__(self, user_repository: UserRepositoryMeta, photo_repository: PhotoRepositoryMeta):
self.user_repository: UserRepositoryMeta = user_repository
self.photo_repository: PhotoRepositoryMeta = photo_repository

Comment on lines +58 to +68
│ ├── abstraction
│ │ ├── __init__.py
│ │ ├── analytics
│ │ │ ├── __init__.py
│ │ │ └── services.py
│ │ ├── photo
│ │ │ ├── __init__.py
│ │ │ └── repositories.py
│ │ └── user
│ │ ├── __init__.py
│ │ └── repositories.py
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For such simple app example, I'd move everything into interfaces.py to keep app structure from bloating.

@abc.abstractmethod
def get_photos(self, user_id):
"""Must be implemented in order to instantiate."""
pass
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Suggested change
pass

Coverage report treats pass as a code. Which never executes for abstractmethods.

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2 participants