Suggestion: default values for models

[Alexander Kurakin]

ROR doesn't realize functionality of setting default values for models. We can use db's default values but they are evaluated during migrations. We can't set default value i.e. Time.now. But there are completed gems that realize this. I.e. default_value_for (https://github.com/FooBarWidget/default_value_for). Why not to merge it in rails? Thanks.

[Luís Ferreira]

Isn't this just the same as having a before_save callback where you define these default values?

Also, what do you mean with "We can use db's default values but they are evaluated during migrations"?

On Oct 17, 2012, at 8:28 PM, Alexander Kurakin wrote:

ROR doesn't realize functionality of setting default values for models. We can use db's default values but they are evaluated during migrations. We can't set default value i.e. Time.now. But there are completed gems that realize this. I.e. default_value_for (https://github.com/FooBarWidget/default_value_for). Why not to merge it in rails? Thanks.

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Cumprimentos,

Luís Ferreira

[Gabriel Sobrinho]

That is a problem for me either.

I can't use before_save callback because I need to show the default value on forms.

So, I have a date field and the default value is today, but when user open the form, today must be on that field.

I'm setting this kind of default value on controller like that:

def new

  @payment = Payment.new

  @payment.date = Date.current

end

But this become a mess since I have "dynamic" default values in almost every model of my application.

[Allen Madsen]

This is relevant: http://stackoverflow.com/questions/328525/what-is-the-best-way-to-set-default-values-in-activerecord

They mention using after_initialize.

Allen Madsen
http://www.allenmadsen.com

To view this discussion on the web visit https://groups.google.com/d/msg/rubyonrails-core/-/Q5Pjbb3Oow0J.

[G. Sobrinho]

Using a after initialize does not respect if you set the attribute to
nil, like this:

Payment.new(:due_date => nil)


Also, it will mutate the already persisted objects if they are
persisted using a nil due date for example.


Another problem happens when you select specific attributes like:

Payment.select(:id, :person_id).first

It raises an exception on after initialize hook because there is no
due date attribute :(

--
Cheers,

Gabriel Sobrinho

[Matt Jones]

On Oct 18, 2012, at 8:50 AM, Gabriel Sobrinho wrote:

> That is a problem for me either.
>
> I can't use before_save callback because I need to show the default value on forms.
>
> So, I have a date field and the default value is today, but when user open the form, today must be on that field.
>
>
> I'm setting this kind of default value on controller like that:
>
> def new
> @payment = Payment.new
> @payment.date = Date.current
> end

One method I was surprised to not see on Stack Overflow - overriding the accessor:

class Payment < AR::Base

def date
super || write_attribute(:date, Date.current)
end

end

This still has the issue identified by G. Sobrinho, however, where explicitly setting an attribute to nil doesn't work quite right.

--Matt Jones