Limiting the number of related records (has_many, but max number?)

[John Lahr]

Can you limit the number of related records a given parent record has?

Example.  Class/Student relatoinship.  A Class has_many students but I want to limit the size of a class to a max 30 (of course minimum or exact numbers would hopefully work the same way?)

[Colin Law]

There may be a better way but I would just use a validation that
prevents further students being added to the class when the limit is
released.

By the way, can a student be in more than one class? If so then you
need has and belongs to many or (which I prefer) has many through.

Colin

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[John Lahr]

Colin

Thanks for your answer.  The student/class thing was just an example - the actual stuff I'd be building has nothing to do with students and classes it was just the easiest thing that came to me.

You can do a validation on a total number of related records?  I did not know that.

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[Colin Law]

On 1 July 2015 at 17:16, John Lahr <john...@gmail.com> wrote:
> Colin
>
> Thanks for your answer. The student/class thing was just an example - the
> actual stuff I'd be building has nothing to do with students and classes it
> was just the easiest thing that came to me.
>
> You can do a validation on a total number of related records? I did not
> know that.

You can write a custom validation to do anything you like. The world
is your mollusc.

Colin

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[John Lahr]

I did not know you could write custom validations.  Still learning

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[Hassan Schroeder]

On Wed, Jul 1, 2015 at 10:40 AM, John Lahr <john...@gmail.com> wrote:
> I did not know you could write custom validations.

... which probably means you are ignoring an extremely valuable
learning resource: the Rails Guides.

e.g. http://guides.rubyonrails.org/active_record_validations.html

HTH,
--
Hassan Schroeder ------------------------ hassan.s...@gmail.com
http://about.me/hassanschroeder
twitter: @hassan
Consulting Availability : Silicon Valley or remote

[John Lahr]

Admittedly I haven't gotten through all of them as I'm still working through the basics...