Thank you, as always, for both the specific answer and the general advice.
Much appreciated!
On Sunday, June 23, 2019 at 5:19:49 PM UTC-5, Mike Bayer wrote:
>
>
>
> On Sun, Jun 23, 2019, at 5:45 PM, Andrew Martin wrote:
>
> 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:
>
>
> you can inspect a ColumnElement structure to look for a certain column
> like this:
>
> from sqlalchemy.sql import visitors
> for elem in visitors.iterate(Project.usergroup == User.usergroup, {}):
> if isinstance(elem, Column) and elem.name == "is_deleted":
> return True
>
> internally, the ORM usually uses visitors.traverse(expression, {},
> {"column": visit_column}) but the above is easier to illustrate quickly.
>
> If it were me, I'd likely keep this as an explicit option on read_all(),
> e.g. read_all(... include_deleted=True), much simpler and won't be called
> "magic" by anyone, but it can go either way.
>
> also if you know me at all you'd know I would not do the "s.commit()"
> inside all of the CR/U/D methods. Your methods that do a "read()" are
> beginning a transaction and leaving it open implicitly (there's no
> rollback() or commit() at the end, nor should there be), whereas your CRUD
> methods are fully committing the transaction for individual
> INSERT/UPDATE/DELETE statements, and this inconsistency and the difficulty
> it introduces in what happens when multiple CRUDService methods are called
> sequentially will eventually lead to architectural problems.
>
>
>
>
> 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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> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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