Set default value in field dependant on another model?

[Lachlan Musicman]

We have two models: Resources and Quota

Resources model instances include:

- red things

- yellow things 

- blue things

Quota have two fields, one is a FK to a Resource, the other is "desired quota".

When instantiating the Quota request form, we create a form for each Resource.

I'd like to autofill the "desired quota" field on each form, but make it dependent on which Resource it is representing.

IE, when someone makes a resource request, we expect them to want

1 red thing

5 yellow things

10 blue things

Do some searching, there's a lot pointing to Signals, but I remember someone once saying "if you are using signals, you should re-write you logic" or somesuch, so I thought I'd ask here.

FWIW - and this is well beyond my control - we are on Django 1.8

Cheers

L.

--

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[Michal Petrucha]

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On Mon, Jan 14, 2019 at 04:05:27PM +1100, Lachlan Musicman wrote:
> We have two models: Resources and Quota
>
> Resources model instances include:
> - red things
> - yellow things
> - blue things
>
> Quota have two fields, one is a FK to a Resource, the other is "desired
> quota".
> When instantiating the Quota request form, we create a form for each
> Resource.
>
> I'd like to autofill the "desired quota" field on each form, but make it
> dependent on which Resource it is representing.
>
> IE, when someone makes a resource request, we expect them to want
>
> 1 red thing
> 5 yellow things
> 10 blue things
>
> Do some searching, there's a lot pointing to Signals, but I remember
> someone once saying "if you are using signals, you should re-write you
> logic" or somesuch, so I thought I'd ask here.
>
> FWIW - and this is well beyond my control - we are on Django 1.8

Hi Lachlan,

This sounds like logic that would be triggered by the view handling
the form – when you're displaying a new empty form, ask your business
logic layer for the default number of things to request in a new
“Quota” for that specific resource, and then pass that number to your
form as the “initial” argument.

Cheers,

Michal
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