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Add an example for class-based service
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README.md
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README.md
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@ -516,6 +516,120 @@ As you can see, this service calls 2 other services - `profile_create` and `conf
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In this example, everything related to the user creation is in one place and can be traced.
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**Additionally, we can have "class-based" services**, which is a fancy way of saying - wrap the logic in a class.
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Here's an example, taken straight from the [Django Styleguide Example](https://github.com/HackSoftware/Django-Styleguide-Example/blob/master/styleguide_example/files/services.py#L22), related to file upload:
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```python
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class FileDirectUploadService:
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"""
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This also serves as an example of a service class,
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which encapsulates 2 different behaviors (create & update) under a namespace.
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Meaning, we use the class here for:
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1. The namespace
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2. The ability to reuse `_infer_file_name_and_type` (which can also be an util)
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"""
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def __init__(self, user: BaseUser, file_obj):
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self.user = user
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self.file_obj = file_obj
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def _infer_file_name_and_type(self, file_name: str = "", file_type: str = "") -> Tuple[str, str]:
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if not file_name:
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file_name = self.file_obj.name
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if not file_type:
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guessed_file_type, encoding = mimetypes.guess_type(file_name)
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if guessed_file_type is None:
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file_type = ""
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else:
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file_type = guessed_file_type
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return file_name, file_type
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@transaction.atomic
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def create(self, file_name: str = "", file_type: str = "") -> File:
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file_name, file_type = self._infer_file_name_and_type(file_name, file_type)
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obj = File(
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file=self.file_obj,
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original_file_name=file_name,
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file_name=file_generate_name(file_name),
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file_type=file_type,
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uploaded_by=self.user,
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upload_finished_at=timezone.now()
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)
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obj.full_clean()
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obj.save()
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return obj
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@transaction.atomic
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def update(self, file: File, file_name: str = "", file_type: str = "") -> File:
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file_name, file_type = self._infer_file_name_and_type(file_name, file_type)
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file.file = self.file_obj
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file.original_file_name = file_name
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file.file_name = file_generate_name(file_name)
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file.file_type = file_type
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file.uploaded_by = self.user
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file.upload_finished_at = timezone.now()
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file.full_clean()
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file.save()
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return file
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```
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As stated in the comment, we are using this approach for 2 main reasons:
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1. **Namespace.** We have a single namespace for our create & update.
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1. **Reuse** of the `_infer_file_name_and_type` logic.
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Here's how this service is used:
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```python
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# https://github.com/HackSoftware/Django-Styleguide-Example/blob/master/styleguide_example/files/apis.py
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class FileDirectUploadApi(ApiAuthMixin, APIView):
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def post(self, request):
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service = FileDirectUploadService(
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user=request.user,
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file_obj=request.FILES["file"]
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)
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file = service.create()
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return Response(data={"id": file.id}, status=status.HTTP_201_CREATED)
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```
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And
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```python
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@admin.register(File)
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class FileAdmin(admin.ModelAdmin):
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# ... other code here ...
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# https://github.com/HackSoftware/Django-Styleguide-Example/blob/master/styleguide_example/files/admin.py
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def save_model(self, request, obj, form, change):
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try:
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cleaned_data = form.cleaned_data
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service = FileDirectUploadService(
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file_obj=cleaned_data["file"],
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user=cleaned_data["uploaded_by"]
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)
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if change:
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service.update(file=obj)
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else:
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service.create()
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except ValidationError as exc:
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self.message_user(request, str(exc), messages.ERROR)
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```
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### Naming convention
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Naming convention depends on your taste. It pays off to have something consistent throughout a project.
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