[Rails] Re: Make a column data unique for each user_id

Matt Jones wrote in post #1109607:
> On Saturday, 18 May 2013 11:14:35 UTC-4, Denny Mueller wrote:
>>> belongs_to :user
>> 1 0001 1
>> 2 0002 1
>> 3 0001 2
>> 4 0001 3
>> 5 0002 3
>>
>>
>> How can i approach this? Any hints what I have to look for?
>>
>
> validates_uniqueness_of has a 'scope' option that will do exactly what
> you're describing:

Also note that any use of validates_uniqueness_of should also be backed
by unique constraints in the database to prevent race conditions from
causing duplicates.

For more details on race conditions related to uniqueness validations
read the section under "Concurrency and integrity" here:

http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#method-i-validates_uniqueness_of

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