I have a generic CRUDService for my web app. It's a pattern that was
loosely suggested to me by Mike a while back. I've probably not implemented
it the way he intended, but it works pretty well in a pretty small amount
of code.
The main work, however, that needs to be done is in the read_all method. It
needs to be able to handle different filters depending on which view is
calling it. Which it can as it is now. But I want to fidget with the
defaults a little. Basically, I almost never want to show objects that have
been soft deleted. Only admin users/views should be able to fidget with
things that we've "deleted". The way the method works now is that if I
don't pass any filters in at all, it sets a filter to
cls.is_deleted==False. But I'd like to be able to inspect incoming filters.
Say the view looks at the resource context and determines that a view
should only be allowed to see objects based on some ACL rule. I might
create a filter for that view controller that looks like
filters = (Project.usergroup==User.usergroup)
(defining the applicable usergroup for a given context is a separate
service, but the relationship should be obvious, I think?)
and then have the view query with CRUDService.read_all(Project,
request.dbsession, filters). The way I've got it now, that would just
replace the default filter, and I would have to add
Project.is_deleted==False to the tuple of filters every time I call this. I
would like to be able to inspect the filters that are passed into the
read_all (which, honestly, I should rename and call it read_many) method
and say, if there isn't any reference to the is_deleted column in the
filters, then set that as false, otherwise, accept the value in the
function parameter. But I find the filter's tuple values quite opaque. Once
they are instantiated, they are class-specific, and I'm trying to get at a
general way of understanding them. I'll note that this column is guaranteed
to be present in the framework. I've modified the declarative base such
that every object has the is_deleted. I appreciate any help you might be
able to give. It's very likely I'm overthinking this like a numbskull and
the answer is painfully obvious. Here's the service class:
from pyramid.request import Request
from crudites.models.meta import Base
from sqlalchemy.orm.session import Session
from uuid import UUID
from typing import List, Tuple, Dict
from crudites.services.id_service import IDService
class CRUDService:
'''TODO: docstring'''
@staticmethod
def create(cls: Base, s: Session) -> bool:
unique_id, public_id = IDService.create_db_ids()
cls.unique_id=unique_id
cls.public_id=public_id
s.add(cls)
s.commit()
return True
@staticmethod
def read_by_pkid(cls: Base, s: Session, id: int) -> Base:
q = s.query(cls).get(id)
return q
@staticmethod
def read_by_unique_id(cls: Base, s: Session, id: UUID) -> Base:
q = s.query(cls).filter_by(unique_id=id).first()
return q
@staticmethod
def read_by_public_id(cls: Base, s: Session, id: str) -> Base:
q = s.query(cls).filter_by(public_id=id).first()
return q
@staticmethod
def read_all(cls: Base, s: Session, filters: Tuple=None) -> List[Base]:
if not filters:
filters = (cls.is_deleted==False,)
q = s.query(cls).filter(*filters).all()
return q
@staticmethod
def update(cls: Base, s: Session) -> bool:
s.add(cls)
s.commit()
return True
@staticmethod
def delete(cls: Base, s: Session)-> bool:
cls.is_deleted=True
s.add(cls)
s.commit()
return True
Thanks,
-andrew
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