How do I stop a column being updated by model.save?

rubyonrails-talk
1

One of my models has a column that is updated very frequently from a separate process, so it is important that when a record is saved in rails, this column should be left alone. In the update method of the controller I have:

@record = MyModel.find(params[:id]) @record.update_attributes(params[:my_model])

params[:my_model] doesn't have a reference to the column I'm talking about, however, the UPDATE statement produced by update_attributes will still assign a value to this column.

Even though its unlikely, if the separate process updates the record in the time betweent the find, and the update, then the new value will be lost. Is there a way to prevent this from happening?

One option, not very clean and elegant, and probably prone to deadlocks if you update several rows during a transaction, is locking the row & reading its' current value from a before_save callback.

E.g.:

  def before_save     unless self.new_record?       current = self.class.find(self.id, :lock => true) # "select for update", locking row       write_attribute(:some_attribute, current.some_attribute)     end   end

Isak

2

hi david,

have you ever try this: @record = MyModel.find(params[:id]) @record.update_attribute(“your_column”, params[:value])

for updating several column, you could use this instead:

@record.update_attribute(“your_column1”, params[:value1], “your_column2”, params[:value2])

afaik, if you do somethink like this:

@record.update_attributes(params[:value])

then all your column will be updated using apt column-name with array of :value, so that you previous value of column will be lost regardles.

regard,

~inung;

3

sorry david, i’m wrong getting your first message. anyway, have u ever try using attr_accessible? n00b here, just trying to help…:smiley:

regards,

~inung;