Ruby on Rails，验证与字符串连接的属性的唯一性

Question

I have an attribute, :group_name , that has to be validated for uniqueness on the client side. BUT first, I need to attach a string to the attribute and only then validate it. Please, do not ask me why, I need it=)

I have a form:

 <%= form_for Group.new, url: what_to_do_groups_path ,method: :get ,:validate => true do |f| %>
 <div class="field_label">
<%= f.label :group_name%>
</div>
<div class="field">
<%=f.text_field :group_name %>
</div>
<%= submit_tag "Submit",  :commit =>"submit" %>

<br class="clear" />
<br />
<%end%>

controller:

attr_accessible  :group_name
validates :group_name,      :uniqueness => { :case_sensitive => false}

So, the user types in "RedBull". The :group_name has a value of "RedBull". I want to attach a string "_Marc" and only validate (client side) in the database, if there is another group called "RedBull_Marc" How can I do it?

May I do something like this?

validates :group_name+"_Marc",      :uniqueness => { :case_sensitive => false}

And if I have multiple strings to attach in order to check if such groups are already in the database. Like I want to check if "RedBull_Marc" or "RedBull_Kate" are in the database So I can do it with regex, like this : /_(Marc|Katja)/ but where should I build it?

Thanks in advance.

edit:
Client side validation should be present.

Answer 1

You could use a before_validation hook to modify the attribute before it gets validated. You could also write your own custom validation that did the concatenation, but it's probably best to use before_validation as that's what it is meant for.

The model:

class User < ActiveRecord::Base
  attr_accessible :group_name

  validates :group_name, :uniqueness => { :case_sensitive => false}

  before_validation :add_to_group_name

  protected
  def add_to_group_name
    self.group_name = group_name + '_Marc' # Edit however you want to here
  end
end

If you need to check the database for multiple values, you won't be able to with just a uniqueness validation, so you'll have to write a custom validation that searches the database for you. For your use case, it looks like you could use a like query:

# % is a wildcard character and matches anything
# So group_name + "%" will match anything starting with group_name
User.where("group_name like ?", group_name + "%") 

So your model would have a custom validation:

class User < ActiveRecord::Base
  attr_accessible :group_name

  validate :check_group_name_uniqueness

  def check_group_name_uniqueness
    if User.where("group_name like ?", group_name + "%").count > 0
      errors.add(:group_name, "is already taken")
    end
  end
end