Seeing that the @values instance variable is heavily used elsewhere in
the code, we have to change the implementation to leave @values alone.
Here is a proposal that will benefit in fixing the documented
shortcomings (it will not benefit in detecting an internal
modification of an attribute value using a ! method):
class Model
# allows user to see original values
def saved_values
@saved_values ||= {}
end
def []=(column, value)
new_value = typecast_value(column, value)
if @values[column] != new_value
@saved_values[column] = @values[column] unless
saved_values.include?(column)
@values[column] = new_value
end
end
def changed_columns
saved_values.keys.find_all {|c| @values[c] != @saved_values[c]}
end
# allows user to see changes indexed by column name
def changes
ret = {}
changed_columns.each {|c| ret[c] = [...@saved_values[c], @values[c]]}
end
end
With this approach, the only performance cost is in #changed_columns,
and it's not that big of a cost.
The only other downside is that the internal modification of a value
problem is magnified here:
# Problematic both before and after new implementation
x = Model.new(:name => 'david')
x.name.gsub! 'david', 'dave'
x.save #=> no change
x.name = 'dave'
x.save #=> no change
# Problematic only in new implementation
x.name = x.name.gsub!('david', 'dave')
x.save #=> no change, but would have changed in previous implementation
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