How to test if is a property is a foreign key

Rails
1

Hi,

How could i test if the property with a certain name, is a foreign key
(the foreign key relation is declared in the model, not in the table)

example:
belongs_to :city, :class_name => “City”, :foreign_key => “CITY_ID”

  • my property for this example is “CITY_ID”
  • i don’t want to test if it has “_id” in the name, the properties
    that are foreign keys may not respect the Class_id rule, further if i
    find that it’s a foreign key, how cand i found the related class.?
  • is there an API command for this?
2

You may find this project interesting.

http://drysql.rubyforge.org/features.htm

Paolo

3

From what i’ve read, right on the first page they are going the other
way I want. Due to the nature of the project i must put the relation in
the model, i’m not allowed to modify the database schema.(and the schema
does not have de fk specified).

4

thank u for the anser, does rails has equivalent for my functions?

knowing an attribute name i want to know if it is used in a belong to

relation

def self.attribute_links_to_a_class?(aatribute)
larray = reflect_on_all_associations(:belongs_to)
lreturn = false
larray.map {|n| if n.primary_key_name.eql?(aatribute);lreturn=true
end}
lreturn
end

knowing an attribute name i want the linked class to be returned

def self.if_attribute_links_to_a_class_return_class(aatribute)
larray = reflect_on_all_associations(:belongs_to)
lreturn = nil
larray.map {|n| if
n.primary_key_name.eql?(aatribute);lreturn=larray.index(n) end}
if lreturn
return Object.const_get(larray[lreturn].class_name.humanize)
else
return nil
end
end

5

On 1/30/07, P. Pantouffe [email protected] wrote:

Reflecting on associations might get you halfway there:

class Account < AR
has_many :users
end

Account.reflect_on_association :users
=> #<ActiveRecord::Reflection::AssociationReflection:0x202491c
@active_record=Account, @primary_key_name=“account_id”,
@macro=:has_many, @name=:users, @options={}>

Account.reflections will show you all associations

Fire up ./script/console and play around.

Hope this helps.

–
Zack C.
http://depixelate.com

6

On 1/31/07, P. Pantouffe [email protected] wrote:

end}
lreturn
end

Here is a one liner that is simpler.

self.reflect_on_all_associations(:belongs_to).map{ |r|
r.primary_key_name }.include?(attr)

else
  return nil
end

end

This syntax might be better suited for your second method:

User.reflections[:account].class_name.constantize

Keep in mind that if the relation is of certain types like :through or
:polymorphic then the class_name() method will throw an error. You’ll
need to check the options {} on the reflection:

reflection.options[:polymorphic] || reflection.options[:through]

It might help to play around in ./script/console with your models to
check out the varying behaviour.

–
Zack C.
http://depixelate.com