By: Bruce Bahlmann - Contributing Author (your feedback is important to us!)

In rails development, when working with MongoDB, you often have a particular field dependent on another or want to verify that all fields are filled out correctly prior to committing these changes to the database. Fortunately, MongoMapper provides support for this through the use of a custom validation.

Custom validations are contained within the model they pertain and referenced with the call to validate:<name of custom validation function>

[app/models/survey.rb]
class Survey 
  include MongoMapper::Document

  key :name, String
  key :description, String 
  key :author, Hash
  <other model definitions> ...
  
  validate :custom_validation
   
  def custom_validation
    errors.add(:name, "- Survey Name cannot be blank, it is required.") if (name == '')
    errors.add(:endDate, '- End Date has not been selected.') if (active == true) && string_to_date(endDate).nil?
    if !string_to_date(endDate).nil?
      errors.add(:endDate, '- End Date cannot be in the past, it must be sometime in the future.') if (endDate <= DateTime.now)
    end  
  end   
end   

The above entry provides three example validations. The first represents a simple check of the name field and return an error if the name field is blank (name == ''). Note that in this case, the ":name" within the brackets defines the name of the field in error so when such data is returned (in error) to the user, the user will know better what might have went wrong.

The second validation is a little more complicated. It involves a check for the existence of a date (endDate). Since endDate could be nil, you need to handle these fields with more care (test for nil first, then test for a valid value). Once the nil case is off the table (tested/accommodated), moving forward testing other potentially harmful values then becomes easier.

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