[sqlalchemy] Re: Auto filter a relationship?

[Jonathan Vanasco]

I hit send early.  That form should/will work for reading - i use it 
heavily.  I'm not sure how/if it will interact with the collections 
management system (backref/backpopulates, etc).  

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Re: [sqlalchemy] Re: Auto filter a relationship?

[Shawn Adams]

Jonathan, Are you suggesting I use this instead of the association_proxy on
Reservation? Doing so will not let me have duplicate packages in the
collections list. sqa filters them out. To get around that I had to use
the association_proxy.

On Thu, Sep 24, 2015 at 1:37 PM, Jonathan Vanasco 
wrote:

> I hit send early.  That form should/will work for reading - i use it
> heavily.  I'm not sure how/if it will interact with the collections
> management system (backref/backpopulates, etc).
>
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Re: [sqlalchemy] Re: Auto filter a relationship?

[Jonathan Vanasco]

Your use of association_proxy seems odd to me.  That plugin is normally 
used to "cut out" the middleman when using a join with an association 
pattern and avoid a hop/remount a relationship from one object onto another.

With my understanding and use of that plugin, you're basically setting the 
following shortcut, and most other behaviors are a side-effect.

Reservation.packages == Reservation._packages_rel.package

Since ReservationPackage has a primary key on `id`, it should be able to 
handle non-unique combinations.

These 2 both jumps out to me as potential problems :

ReservationPackage-
   package - there is no backref or back-populates.
   package - should this have a uselist=False setting?  
   __init__ - this handles the package, but not the reservation ?

Reservation-
package_rel - no backref or back-populates

In my experience, the bulk of problems with 'collections' have happened 
because of incomplete or improper relationships.  I'd try setting up 
everything with fully declared relationships (ie,  back_populates) and see 
how that affects the design of your relations and how the code runs.

You can pretty much expect the collections to not work properly unless you 
have backref/back-populates declared.  That's the biggest issue and warning 
sign to me -- sqlalchemy only knows half of your relationship info.

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[sqlalchemy] Re: Auto filter a relationship?

[Jonathan Vanasco]

packages = sa.orm.relationship("Package", 
primaryjoin="and_(ReservationPackage.package_id==Package.id, 
Package.deleted IS NOT NULL)")

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Re: [sqlalchemy] Re: Auto filter a relationship?

[Shawn Adams]

Reservation -> packages is just a many-to-many relationship with the caveat
that a reservation can have the same package more than once. Sqlalchemy
will automatically dedube the packages collections which is not what I
want. In order to avoid this I had to use reservation_packages as an
association table instead. The proxy is needed to hide this detail. So
those relationships work fine.

Everything is done through reservation.packages so I don't need all those
extra backrefs. ReservationPackage.__init__ must accept a package object so
that appending to the packages collection works.

On Thu, Sep 24, 2015 at 3:32 PM, Jonathan Vanasco 
wrote:

> Your use of association_proxy seems odd to me.  That plugin is normally
> used to "cut out" the middleman when using a join with an association
> pattern and avoid a hop/remount a relationship from one object onto another.
>
> With my understanding and use of that plugin, you're basically setting the
> following shortcut, and most other behaviors are a side-effect.
>
> Reservation.packages == Reservation._packages_rel.package
>
> Since ReservationPackage has a primary key on `id`, it should be able to
> handle non-unique combinations.
>
> These 2 both jumps out to me as potential problems :
>
> ReservationPackage-
>package - there is no backref or back-populates.
>package - should this have a uselist=False setting?
>__init__ - this handles the package, but not the reservation ?
>
> Reservation-
> package_rel - no backref or back-populates
>
> In my experience, the bulk of problems with 'collections' have happened
> because of incomplete or improper relationships.  I'd try setting up
> everything with fully declared relationships (ie,  back_populates) and see
> how that affects the design of your relations and how the code runs.
>
> You can pretty much expect the collections to not work properly unless you
> have backref/back-populates declared.  That's the biggest issue and warning
> sign to me -- sqlalchemy only knows half of your relationship info.
>
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