在Rails中通过自定义方法对所有记录进行分组

Question

I'd like to retrieve all records for a particular model and "index" each one by their name attribute. The end result should be a Hash, where the keys are the name of the record, and the value is the record. I can do this easy enough with a method like

def self.all_by_name
  hash = {}
  all.each { |model| hash[model.name] = model }
  hash
end

Is there a way to do this with an active record query?

Answer 1

all.group(:name) is what you need!

Some documentation: http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-group

Answer 2

No, active record will either return an array or an active record relation. You would have to massage it after into the data type of your choice. ActiveRecor dcan return anything that SQL can normally return. However, you could do use the group method which is essentially the group by in SQL.

I'm not sure in your case what your method should do because it seems like you are going to overwrite the value of your key if there are 2 objects with the same class. Perhaps if you better defined what you need in an example I could help you better.