Is there any way to check that has_many association exists in Rails 3.1?

Question

For example there are some models

class Model_1 < ActiveRecord::Base
   has_many :images, :as => :imageable
end

class Model_2 < ActiveRecord::Base
   # doesn't have has_many association
end
...
class Image < ActiveRecord::Base
    belongs_to :imageable, :polymorphic => true
end

How can I check that model has has_many association? Something like this

class ActiveRecord::Base
    def self.has_many_association_exists?(:association)
        ...
    end
end

And it can be used so

Model_1.has_many_association_exists?(:images) # true
Model_2.has_many_association_exists?(:images) # false

Thanks in advance

Solution 1

What about reflect_on_association?

Model_1.reflect_on_association(:images)

Or reflect_on_all_associations:

associations = Model_1.reflect_on_all_associations(:has_many)
associations.any? { |a| a.name == :images }

Solution 2

I found the following to be the simple way to achieve the desired result:

ModelName.method_defined?(:method_name)

Example:

Model_1.method_defined?(:images) # true
Model_2.method_defined?(:images) # false

Reference: https://stackoverflow.com/a/18066069/936494

Solution 3

You could probably use respond_to?

class ActiveRecord::Base
    def self.has_many_association_exists?(related)
        self.class.associations.respond_to?(related)
    end
end

Comments

[KARASZI István]

That could be a method, or attribute, or anything. Not an association. But yes, duck typing :)

[ktec]

I'd probably go with KARASZI István's answer!

[Babur Ussenakunov]

Thanks a lot! Exactly what I needed)

[Ricardo Vila]

This aproach is not fully compliant. Try it with :destroy, for example. Is not a relation but te object has this method.