Add find :unique to ActiveRecord

So, I read the bar at the right :)
So, I didn't test this, I just typed it here, so I'm not sure if my manual diff is ok. anyway.. here's the code:

In base.rb from activerecord:

in find(*args):

    case args.first
      when :first  then find_initial(options)
      when :all    then find_every(options)

•   when :unique then find_unique(options)
  

add method:

    def find_initial(options)
      options.update(:limit => 1) unless options[:include]
      find_every(options).first
    end

•  def find_unique(options)
  

•    records = find_every(options)
  

•    if records.size > 0 then
  

•      raise ActiveRecordError, "Too many records found: #{records.size}"
  

•    end
  

•    records.first
  

•  end
  

Also, some calls to find_initial should be replaced by find_unique, but I can imagine that would break some existing apps. So that might be for later.

So, I read the bar at the right :)
So, I didn't test this, I just typed it here, so I'm not sure if my manual diff is ok. anyway.. here's the code:

In base.rb from activerecord:

in find(*args):

        case args.first

      when :first  then find_initial(options)
      when :all    then find_every(options)

•   when :unique then find_unique(options)</code>
  

add method:

        def find_initial(options)

      options.update(:limit => 1) unless options[:include]
      find_every(options).first
    end

•  def find_unique(options)
  

•    records = find_every(options)
  

•    if records.size > 0 then
  

•      raise ActiveRecordError, "Too many records found: #{records.size}"
  

•    end
  

•    records.first
  

•  end</code>
  

Also, some calls to find_initial should be replaced by find_unique, but I can imagine that would break some existing apps. So that might be for later.

Hey Joris,

I think you should discuss this change in the ML first. Also, your patch should have tests. Check http://guides.rubyonrails.org/contributing_to_rails.html for more details.

Thanks!

is this really the proposed implementation?

def find_unique(options)
  records = find_every(options)
  if records.size > 0 then

raise ActiveRecordError, "Too many records found: #{records.size}"

  end
  records.first
end

Seems a bit crazy,
I'd rather have the two db calls (count, and find_first)

Also, I don't get the use-case.
Joris, do you have some examples of how you are using this feature?

The only reason I've needed something similar is this case;

class SomeSortOfSettings < ActiveRecord::Base
  def self.instance
    self.first || self.new
  end
end

namely a "Singleton" ActiveRecord,
but I think there's a better way to deal with this
(an ActiveRecord::Singleton class, perhaps)

User.find(:unique, :conditions => {:username => "ralph"})

is silly,
you should just have a unique key on :username

Having 2 queries would be a waste of db calls. If you expect 1 row, there's no need to do a count.

All queries for something with a unique index / natural key is where I'd do this. Just because it's contextual more correct, and it has no performance drawbacks except for a single check if there's another row in the resultset.

The implementation was just something I typed. I can imagine that there would be some other things that would need to happen, but basically that's how about what I had in mind.

Hibernate has a similar feature: query.uniqueResult