In rubyonrails, how to get the associated model class from and ActiveRecord::Relation object?

问题

Suppose I have an model:

class Post
end  

posts = Post.where(***)  
puts posts.class # => ActiveRecord::Relation  

Then how can I get the model class name through the variable 'posts', maybe some method called model_class_name:
puts posts.model_class_name # => Post

Thanks :)

回答1:

The #klass attribute of ActiveRecord::Relation returns the model class upon which the relation was built:

arel = User.where(name: "fred")
arel.klass    # User

To get the class's name:

arel.klass.name

Tested in ActiveRecord 4.2.4

回答2:

For a solution that works, even if there are no related items:

class Post < ActiveRecord::Base
   has_many :comments
end

Post.reflect_on_association(:comments).klass
=> Comment

回答3:

The most simple and direct answer to your question is:

posts.first.class.name

Which is equivalent to writing:

posts.[0].class.name

You can do this because your query will return an enumerable result. (ActiveRecord::Relation implements Ruby's Enumerable interface).

-- Scott

来源：https://stackoverflow.com/questions/4263844/in-rubyonrails-how-to-get-the-associated-model-class-from-and-activerecordrel