How do I do conditional validation in ActiveRecord with n conditions?

Question

I am providing a web service to be called by external companies. The required data covers several models including person, address etc. I want to validate the received data conditionally based upon some fields within the request. I will eventually have many differing sets of validation data, although currently I only have one and I am about to add the second.

My current model looks something like this

class Person < ActiveRecord::Base
    validates_length_of :first_name, :within => 1..32, :allow_blank => true
    ...
    ...
end

Conceptually my model now needs to do something like this.

class Person < ActiveRecord::Base
    validate :first_name?  

    def first_name?
        if country == 'UK'
            if company_name == 'ABC'
                validates_length_of :first_name, :within => 1..32
            else if company_name == 'DEF'
                validates_length_of :first_name, :within => 2..20
            end
        else if country == 'DE'
             if company_name == 'ABC'
                validates_length_of :first_name, :within => 1..32
            else if company_name == 'DEF'
                validates_length_of :first_name, :within => 2..20
            end
    end
end

This would obviously work fine for 2 companies/countries but will not work well as the number of companies and/or countries increases. I am now considering keeping the validation data either in the database or in a YAML file and then performing the validations manually for each field based upon the minimum, maximum, format values stored externally from the model.

I am thinking that I could store the validation data in a structure similar to the following

country: UK
    companyname: ABC  
        field: first_name  
            minimum_length: 2  
            maximum_length: 20  
            required: true  
        field: middle_name  
            minimum_length: 1  
            maximum_length: 10  
        field: email_address  
            minimum_length: 10  
            format: /someregexforemail addresses/

    companyname: DEF
        field
           ...
country: DE
    companyname: XYZ
       field: 
         ....  

and so on.

I could then load this validation data and use this within my own hand-rolled validator.

Has anyone done similar things in the past and what methods did you use? I am particularly interested to know how you approached the following.

• Where did you store your configuration data i.e. DB or YAML?
• Did you load and parse the configuration data for each request or once as the server loaded?
• How did you structure the actual method that did validation?

Answer 1

I did something similar with phone numbers. Your approach is very similar to what I did myself. To answer your questions:

1. I stored the validation configuration in a YAML file. Hovewer, if your data is going to grow to a large extent, you should consider using database.
2. I load and parse data on each request. I don't think that's the best approach, though and plan to rewrite this part.
3. I wrote my own validation. You can get come clue how to do that here.

Did that help you?