In Rails, is there a way to tell TYPE what attr_accessor should be and check it using the built-in validation of Rails?

Question

I never managed to find a good way to do this, so I thought I'd ask.

For example, in an ActiveRecord model, the attributes supported by the database are automatically converted by type to the corresponding database types. If I have a Category model and it has several attributes, say name and category_id , if I like this:

 Category.new(params[:category]) 

Rails knows that name is a string, and category_id is an integer.

Let's say I have some transient / synthetic attributes that I want to test, and they have certain types. I want to send them from a form, and I would like them to automatically convert to String or Integer or Date (for example) depending on how they are defined.

If I were to declare something in a Rails model, for example:

 attr_accessor :some_number_variable attr_accessor :some_date 

Is there a built-in way to tell Rails “I would like you to port the former to Integer and the latter to Date when I go Category.new(params[:category]) ” while params[:category][:some_number_variable] and params[:category][:some_date] are part of the data presented to the controller (I understand that the Date example can be a little more complicated considering the many date formats there).

Answer 1

None of the answers answer the question. I believe that the correct answer to the questions is simply "No." The answers both guide possible workarounds to the fact that the answer to the question is “No,” and both are valid comments / ideas.

Answer 2

attr_accesor just creates read / write methods, and it comes from Ruby , not Rails. The Rails method, which I think is often confused, is attr_accessible , which serves another purpose . If you want to use when an attribute is being read, you can simply override the reader.

 attr_accessor :some_number_variable def some_number_variable @some_number_variable.to_i end 

This will at least give you a writer for free. This is the best solution that I know for what (I think) you are describing.

EDIT. Regarding validation, I believe that if you use Rails 3, it will be much easier for you to check for these attributes (I did not, so I can’t say for sure). Now that the checks are not tied directly to ActiveRecord, I believe that this is possible.

Answer 3

I assume that the transition / synthetic attribute means a virtual attribute?

If so, there is no built-in Rails function that will do this, which I can think carelessly, but one solution would be to simply write a module for these attributes and include it in the model. Or, if it should be dynamic, you can call an attribute something like: some_variable_integer, and then process these dynamic attributes with the method_missing method, read the method name and convert it to the required type.

In my opinion, this is a little dirty, so validations in the model are really best if what you want to do can support them.

Answer 4

use before_create ..

 class Category attr_accessor :some_number_variable, :some_date before_create :validate private def validate return unless !!params[:category] #do variable casting here end end 

Answer 5

Add to your model:

 columns_hash["birth_date"] = ActiveRecord::ConnectionAdapters::Column.new("birth_date", nil, "date") 

reference: Rails ActiveRecord :: MultiparameterAssignmentErrors