Attribute Values in Rails

Setting attribute values in Rails is harder than I'd expect it to be. With Core Data/Cocoa, I'd do something like this pseudocode-ish code:

- (void) scrubAttributes
{
   id attributes = [[self entityDescription] attributesByName];
   id key, value, e = [attributes keyEnumerator];
  
   while (key = [e nextObject]) {
      value = [NSMutableString stringWithString:[self valueForKey: key]];
      [value stripWhitespace];
      [value collapseWhitespace];
      [self setValue: value forKey: key];
   }
}

This is "the way" to do it in Cocoa. More verbose than Ruby, but it's clear what's going on. In a Rails app, accessing attribute values takes a few different forms. Let's assume there's an ActiveRecord subclass with "first_name" and "last_name" as attributes. I could get to the attribute values any of the following ways:

puts @first_name, @last_name

puts self.first_name, self.last_name

first = "first_name"
last  = "last_name
puts self.attributes[first], self.attributes[last]

As far as I can tell, self.key and self.attributes[key] do the same thing, but @key only grabs whatever is in memory -- it won't trigger any sort of faulting. (Don't take this as truth, it's just what I can gather from what I've read.) This is where the principle of least surprise seems to be absent a bit. These syntactical differences can cause a lot of confusion.

Now, what if I want to process a group of attributes at once? I thought since Ruby is OO, this might work:

def scrub_attributes
  self.attributes.each do |key,value|
    if value.is_a?(String)
      value.strip!
      value.squeeze!(" ")
    end
  end
end

Nope. No errors, but the changes don't get written to the parent. I guess these things that are passed into the block are copies? Next, I tried this:

def scrub_attributes
  self.attributes.each do |key,value|
    if value.is_a?(String)
      self.attributes[key].strip!
      self.attributes[key].squeeze!(" ")
    end
  end
end

Nope, same deal as last time. Then I though for sure this would work:

def scrub_attributes
  self.attributes.each do |key,value|
    if value.is_a?(String)
      value.strip!
      value.squeeze!(" ")
      self.attributes[key] = value
    end
  end
end

But once again, nothing happened. This was really surprising and I wasted a lot of time trying to figure it out. Finally, I got it to work like this:

def scrub_attributes
  values = {}
  self.attributes.each do |key,value|
    if value.is_a?(String)
      value.strip!
      value.squeeze!(" ")
      values[key] = value
    end
  end
  self.attributes = values
end

So technically it works, but it doesn't feel as elegant as other Ruby code. I found a slightly more compact solution:

def scrub_attributes
  self.attributes.each do |key,value|
    if value.is_a?(String)
      value.strip!
      value.squeeze!(" ")
      write_attribute key, value
    end
  end
end

So that's what I ended up with, but I'd still really like to know what I can't write to the self.attributes hash. In an effort to learn more about the language, is there an even-more-elegant-yet-still version of the above?

Update

I made this a bit easier by adding code to the String class. I created file called stringextensions.rb in the application's "lib" folder and added this:

class String
  def minimize_whitespace!
    self.strip!
    self.squeeze!(" ")
  end
end

Adding code to an existing class is just that easy. Now i can use it like this:

require "lib/stringextensions"

def scrub_attributes
  self.attributes.each do |key,value|
    if value.is_a?(String)      
      value.minimize_whitespace!
      write_attribute key, value
    end
  end
end

This is pretty good, but I still wonder if I can eliminate that if qualifier on the end by adding the method to the Ruby base class. I need to find out if that will work for nil objects, though.

Speaking of which, I was surprised that sending messages to nil generates exceptions in Ruby, at least in Rails development mode. I  think ignoring nil messages saves a lot of time in Objective-C.

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