the before_compile event receives the Query object at the point it starts to
turn it into a SQL construct. When this happens, it's in response to having
said something like "query.all()". So there's no **kwarg that's specific to
an operation like that.
instead, when you want to send "messages" to event handlers like
before_compile(), you have to do it by altering the state of the Query itself.
Your suggestion to say "query.filter_by(archived=True)" is actually such a
state change, which would be altering the "_criterion" attribute to include the
"archived=True" criteria, but to consume this attribute to search for this
specific criteria would be tedious and possibly error prone.
instead, you can stick with a simpler way to change the state of the Query in a
way that you can detect inside your event handler easily. Probably the
simplest is to use the query.execution_options() method, where you can add
arbitrary keys and values that can be read later on:
query = query.execution_options(include_archived=True)
in your handler you can check it just like thisL
def filter_archived(query):
if not query.get_execution_options().get("include_archived", False):
# modify the query
in SQLAlchemy 1.4 which is to be released any day now, there's a much more
comprehensive event / API for this kind of alteration, see the example at
https://docs.sqlalchemy.org/en/14/_modules/examples/extending_query/filter_public.html
which is the latest version of this pattern, which includes the use of
execution_options to affect the state of the event handler.
On Mon, Mar 1, 2021, at 6:18 PM, Chris Simpson wrote:
> Hello
>
> I'd like to understand how to turn off a before_compile listener (e.g. soft
> delete, to include deleted items).
>
> For example,
>
> I've adapted the example from the docs:
> https://docs.sqlalchemy.org/en/13/orm/events.html?highlight=before_compile#sqlalchemy.orm.events.QueryEvents.before_compile
>
>
> To use the field 'archived' , which works as expected.
>
> @event.listens_for(Query, "before_compile", retval=True, bake_ok=True)
> def filter_archived(query):
> for desc in query.column_descriptions:
> if desc["type"] is Person:
> entity = desc["entity"]
> query = query.filter(entity.archived == 0)
> return query
>
>
> I've tried things such as:
>
> Person.query.filter_by(archived=True).all()
>
> But I don't understand yet where I should put such kwargs to override the
> before_compile events listener
>
> Is the following the right path?
>
> @event.listens_for(Query, "before_compile", retval=True, bake_ok=True)
> def filter_archived(query, **kwargs):
> for desc in query.column_descriptions:
> if kwargs["include_archived"] is not True and desc["type"] is Person:
> entity = desc["entity"]
> query = query.filter(entity.archived == 0)
> return query
>
>
> Kind regards
> Chris
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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