WL-327: Add SiteConfiguration and SiteConfigurationHistory models to LMS

[saleem-latif]

Hi @asadiqbal08 , @mattdrayer ,

Kindly review this PR, change set contains addition of SiteConfiguration model to theming app.

Description of Changes:
Add a new SiteConfiguration Model to theming app which would link to Django site in OneToOne relationship for persisting site specific configurations. This model can have a JSONField to keep configurations in JSON. To persist each change to this model we can add a separate Model SiteConfigurationHistory which should persist history of SiteConfiguration model. We can copy data from SiteConfiguration to SiteConfigurationHistory on post_save signal of SiteConfiguration model.

class SiteConfiguration(models.Model):
    site = models.OneToOneField(Site, related_name='configuration')
    values = JSONField(null=False, blank=True, load_kwargs={'object_pairs_hook': collections.OrderedDict})

class SiteConfigurationHistory(TimeStampedModel):
    site = models.ForeignKey(Site, related_name='configuration_histories')
    values = JSONField(null=False, blank=True, load_kwargs={'object_pairs_hook': collections.OrderedDict})

[mattdrayer]

We need to include a set of tests to cover this workflow

[tobz]

Does it make sense to build on top of ConfigurationModel here? It would give you history for free, and you could write custom methods to handle JSON serialization/deserialization.

[saleem-latif]

@tobz I looked at the ConfigurationModel model here and I do not think it would be good fit in this scenario.

[mattdrayer]

I'm thinking that these models should live somewhere outside of theming -- I'd prefer to add it to edx-django-sites-extensions, but it would result in a conflict with the existing SiteConfiguration model present in Otto/ecommerce. If we keep these specific to edx-platform perhaps we add a new module to edx-platform/openedx/core/models?

[saleem-latif]

@mattdrayer I have incorporated your feedback changes, kindly take a look

[mattdrayer]

@douglashall, FYI

[mattdrayer]

I wasn't able to comment directly on the __init__.py file because it contains no lines -- can you please add a docstring to this module explaining the purpose of the new app and some details about the models and how to use them?

[mattdrayer]

Please add a leading comment

[mattdrayer]

@saleem-latif overall I think this change set looks good -- we need to improve context/understanding through better comments and docstrings, but as far as the implementation goes we are on the right track.

[douglashall]

👍 from me once @mattdrayer's comments are addressed.

[saleem-latif]

@mattdrayer I have updated existing comments and added some new doc strings, kindly take a look

[mattdrayer]

Looks great -- 👍