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Smells like ActiveRecord messes object attributes on save

Answer 1

+1 A:

You are modifying the same object here:

l.old_feed = l.feed
l.feed.sub!(/^.*?(\d+)\.xml$/, 'http://newsrss.bbc.co.uk/weather/forecast/\1/Next3DaysRSS.xml') # l.feed = l.feed.sub(...) does not make it any better

it should be instead:

l.old_feed = l.feed.clone
l.feed.sub!(/^.*?(\d+)\.xml$/, 'http://newsrss.bbc.co.uk/weather/forecast/\1/Next3DaysRSS.xml') # l.feed = l.feed.sub(...) does not make it any better

KARASZI István 2010-01-12 16:57:26

That doesn't seem to explain why feed retains old value.

artemave 2010-01-12 17:12:46

Maybe some internals mixed up, but the problem lies there I think.

KARASZI István 2010-01-12 17:23:49

You are right. molf answer explains why feed stayed the same.

artemave 2010-01-12 17:32:22

Answer 2

+2 A:

You are modifying the same object (mentioned already).
The feed attribute is not assigned anything new. You are modifying the return value in place.

These combined makes it look like you are reversing the strings. Funny, outcome actually. :-)

Try this instead:

def self.up
  add_column :locations, :old_feed, :string
  Location.all.each do |l|
    l.old_feed = l.feed
    # Reassign the new feed and drop the ! from sub!() to return a new string.
    l.feed = l.feed.sub(/^.*?(\d+)\.xml$/,
      'http://newsrss.bbc.co.uk/weather/forecast/\1/Next3DaysRSS.xml')
    l.save!
  end
end

molf 2010-01-12 17:10:52

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Smells like ActiveRecord messes object attributes on save

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