在Rails上获取不同用户的最新记录

Question

The database is something like this:

id testID date
1  100    10/12/2012
2  100    10/13/2012
3  102    10/14/2012

Let's call this database "Test"

I want the output to be an ActiveRecord:Relation that contains

id testID date
2  100    10-13-2012
3  102    10-14-2012

I know how to get the results as an array, as following:

result = []
testIDList = Test.uniq.pluck(:testID)
testIDList.each do |tID|
    result = result + Test.where(:testID => tID).order('date DESC').limit(1)
end

In this case, result is an array of ActiveRecord:Relation But I want result to be an ActiveRecord:Relation, I tried to use merge no success.

Answer 1

尝试

   result = Test.order(:date).group(:testID)

Answer 2

Try this:

result = Test.where(:testID => testIDList)
             .select("max(`date`) as recent_date").group(:testID)