rails - activerecord ... grab first result

Question

I want to grab the most recent entry from a table. If I was just using sql, you could do

Select top 1 * from table ORDER BY EntryDate DESC

I'd like to know if there is a good active record way of doing this.
I could do something like:

table.find(:order => 'EntryDate DESC').first

But it seems like that would grab the entire result set, and then use ruby to select the first result. I'd like ActiveRecord to create sql that only brings across one result.

Answer 1

You need something like:

Model.first(:order => 'EntryDate DESC')

which is shorthand for

Model.find(:first, :order => 'EntryDate DESC')

Take a look at the documentation for first and find for details.

Answer 2

The Rails documentation seems to be pretty subjective in this instance. Note that .first is the same as find(:first, blah...)

From:http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M002263

"Find first - This will return the first record matched by the options used. These options can either be specific conditions or merely an order. If no record can be matched, nil is returned. Use Model.find(:first, *args) or its shortcut Model.first(*args)."

Digging into the ActiveRecord code, at line 1533 of base.rb (as of 9/5/2009), we find:

    def find_initial(options)
      options.update(:limit => 1)
      find_every(options).first
    end

This calls find_every which has the following definition:

    def find_every(options)
      include_associations = merge_includes(scope(:find, :include), options[:include])

      if include_associations.any? && references_eager_loaded_tables?(options)
        records = find_with_associations(options)
      else
        records = find_by_sql(construct_finder_sql(options))
        if include_associations.any?
          preload_associations(records, include_associations)
        end
      end

      records.each { |record| record.readonly! } if options[:readonly]

      records
    end

Since it's doing a records.each, I'm not sure if the :limit is just limiting how many records it's returning after the query is run, but it sure looks that way (without digging any further on my own). Seems you should probably just use raw SQL if you're worried about the performance hit on this.

Answer 3

Could just use find_by_sql http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M002267

table.find_by_sql "Select top 1 * from table ORDER BY EntryDate DESC"