Define a string as a Model object

rubyonrails-talk
1

Good morning,

I'm trying to dynamically define models.

This method #1 works: model_name = User @Model = model_name @Model.find(params[:id]).name

This method #2 doesn't: model_name = "User" @Model = model_name @Model.find(params[:id]).name

Anyone know how I can get method #2 to work? Is there something I can tack onto the end of 'model_name' to get it to know that it's a model?

Thanks,

Frank

2

Try the eval method.

For instance:

classname = "Date" => "Date" eval(classname).today => Fri, 05 Feb 2010

3

Frank_in_Tennessee wrote:

Good morning,

I'm trying to dynamically define models.

This method #1 works: model_name = User @Model = model_name @Model.find(params[:id]).name

This method #2 doesn't: model_name = "User" @Model = model_name @Model.find(params[:id]).name

Of course not. In method 2, @Model is a String, not a Class.

Anyone know how I can get method #2 to work? Is there something I can tack onto the end of 'model_name' to get it to know that it's a model?

Look up the constantize method.

Thanks,

Frank

Best,

4

Try the eval method.

For instance:

classname = "Date" => "Date" eval(classname).today => Fri, 05 Feb 2010

With ActiveSupport you get constantize.

constantize("Date")

=> Date

You can either look at the ActiveSupport implementation or this one:

   # from Jim Weirich (based on email correspondence), improved by Rick Denatale (in ruby-talk:332670)    def constantize(camel_cased_word)      camel_cased_word.        sub(/^::/,'').        split("::").        inject(Object) { |scope, name| scope.const_defined?(name) ? scope.const_get(name) : scope.const_missing(name) }    end

-Rob

Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com

5

Works great now. Thank you.

Modified Code:

model_name = "User" @Model = model_name.constantize @Model.find(params[:id]).name

6

Frank_in_Tennessee wrote:

Works great now. Thank you.

Modified Code:

model_name = "User" @Model = model_name.constantize @Model.find(params[:id]).name

Great. One other thing: @Model is unusual. You might consider @model instead as being more idiomatic Ruby.

Best,