有没有办法列出所有belongs_to关联？

Question

我需要在模型对象中列出所有belongs_to关联并迭代它们.有没有办法做到这一点？

Answer 1

您可以使用Reflection中的reflect_on_all_associations方法例如:

Thing.reflect_on_all_associations(:belongs_to)

Answer 2

您可以使用类的reflections哈希来执行此操作.可能有更简单的方法,但这有效:

# say you have a class Thing
class Thing < ActiveRecord::Base
  belongs_to :foo
  belongs_to :bar
end

# this would return a hash of all `belongs_to` reflections, in this case:
# { :foo => (the Foo Reflection), :bar => (the Bar Reflection) }
reflections = Thing.reflections.select do |association_name, reflection| 
  reflection.macro == :belongs_to
end

# And you could iterate over it, using the data in the reflection object, 
# or just the key.
#
# These should be equivalent:
thing = Thing.first
reflections.keys.map {|association_name| thing.send(association_name) }
reflections.values.map {|reflection| thing.send(reflection.name) }

Answer 3

Thing.reflections.collect{|a, b| b.class_name if b.macro==:belongs_to}.compact 
#=> ["Foo", "Bar"]

当然,您也可以传递:has_many或任何其他关联