On Saturday, March 1, 2014 4:29:43 PM UTC-7, Russell Keith-Magee wrote:
>
>
> On Sun, Mar 2, 2014 at 1:07 AM, Aymeric Augustin <
> [email protected] <javascript:>> wrote:
>
>> On 1 mars 2014, at 09:14, Martin Matusiak <[email protected]<javascript:>>
>> wrote:
>>
>> A structural reason is that you can't tell "assigning an attribute to an
>> instance in order to save it to the database later" apart from "assigning
>> an
>> attribute to an instance being loaded from the database". So your proposal
>> doesn't play nice with lazy loading of related instances, for example.
>>
>> Another reason is the impossibility of running validations involving
>> multiple
>> fields. If a validator depends on the value of two fields, one has to be
>> set
>> before the other, and you can't validate at that point.
>>
>
> For me, this is the bigger reason why validation at time of assignment
> isn't viable.
>
> In order to do multi-field validation at time of assignment, we'd need to
> introduce some sort of transactional behaviour. Just thinking about this
> makes my brain hurt.
>
>
Russ
This got me thinking about what the API for doing multi-field validation
could look like. I came up with two ideas that may or may not hold water.
The simplest solution I could think of would be a setter method on the
model that took **kwargs and set them on the model, calling validation
after they've all been set. Kind of a gross API, but it should work.
The maybe cleaner idea would be a context manager that deferred validation
till the end of the context block.
with instance.validation_block():
x = 4
y = 5
Here's a gist that hopefully demonstrates the idea.
https://gist.github.com/pipermerriam/e858cd6f2c2535d8868d
I'm +0 on this idea overall, but I think it'd be nice to have a better
system for model validation than the current state of things. I'm just not
sure what that looks like.
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