Getting class name from association name

Rails
1

Hi

This is difficult (for me, at least :wink: )

I have a model named Measureunit and another named Vendor

Each vendor has a measureunit for the currency it use, and the
association
is currency

In vendor.rb I have
belongs_to :currency, :class_name => “Measureunit” , :foreign_key =>
“currency_id”

How can I recover the class name from the association name (eg. I have
the
string ‘Currency’ and I look for
a method that return ‘Measureunit’)

I found class_name() and klass() but I can’t figure the syntax…

Tnx!

2

On 15 November 2011 18:27, PandaR1 [email protected] wrote:

string ‘Currency’ and I look for
a method that return ‘Measureunit’)

I don’t understand what you mean by ‘I have the string “Currency”’ but
if you have a vendor object then you can say
vendor.currency.class.name

Also I do not understand why you would want to do this so I have
probably misunderstood the question.

Colin

3

On Nov 15, 12:27pm, PandaR1 [email protected] wrote:

belongs_to :currency, :class_name => “Measureunit” , :foreign_key =>
“currency_id”

How can I recover the class name from the association name (eg. I have the
string ‘Currency’ and I look for
a method that return ‘Measureunit’)

I found class_name() and klass() but I can’t figure the syntax…

I believe what you’re saying is that you have the Vendor class, and
the name of the association as a string, ‘Currency’. You want to look
at The ActiveRecord::Reflection documentation, specifically
reflect_on_association (ActiveRecord - APIdock
Reflection/ClassMethods/reflect_on_association). That gives you back
an AssociationReflection, which has a bunch of information for you:
ActiveRecord::Reflection::AssociationReflection - APIdock.
Specifically again, you likely want klass on that, which should return
the class of the association; do be aware that its a little bit more
complex for polymorphic relationships if that’s necessary to support.

So in summary what you likely want is something like
s = “Currency”
association_name = s.underscore # Or
whatever transformation takes your string to your association name
reflection = Vendor.reflect_on_association(association_name) #
Returns the AssociationReflection object
reflection.klass #
Returns the class object, in this case Measureunit

HTH,
\Peter

4

I also want to find the association name dynamically from a dynamic
object. I was looking for something to help me on this. ’
ActiveRecord::Reflection’ a nice module to get association info.

Thanks Peter.

  • Abhi

Peter wrote in post #1032176:

On Nov 15, 12:27pm, PandaR1 [email protected] wrote:

belongs_to :currency, :class_name => “Measureunit” , :foreign_key =>
“currency_id”

How can I recover the class name from the association name (eg. I have the
string ‘Currency’ and I look for
a method that return ‘Measureunit’)

I found class_name() and klass() but I can’t figure the syntax…

I believe what you’re saying is that you have the Vendor class, and
the name of the association as a string, ‘Currency’. You want to look
at The ActiveRecord::Reflection documentation, specifically
reflect_on_association (ActiveRecord - APIdock
Reflection/ClassMethods/reflect_on_association). That gives you back
an AssociationReflection, which has a bunch of information for you:
ActiveRecord::Reflection::AssociationReflection - APIdock.
Specifically again, you likely want klass on that, which should return
the class of the association; do be aware that its a little bit more
complex for polymorphic relationships if that’s necessary to support.

So in summary what you likely want is something like
s = “Currency”
association_name = s.underscore # Or
whatever transformation takes your string to your association name
reflection = Vendor.reflect_on_association(association_name) #
Returns the AssociationReflection object
reflection.klass #
Returns the class object, in this case Measureunit

HTH,
\Peter