Rails: How to check if "update_attributes" is going to fail?

it returns false if it was not done, same with save. save! will throw exceptions if you like that better. I'm not sure if there is update_attributes!, but it would be logical.

just do

if @foo.update_attributes(params)
  # life is good
else
  # something is wrong
end

http://apidock.com/rails/ActiveRecord/Base/update_attributes

Edit

Then you want this method you have to write. If you want to pre check params sanitation.

def params_are_sanitary?
  # return true if and only if all our checks are met
  # else return false
end

Edit 2

Alternatively, depending on your constraints

if Foo.new(params).valid? # Only works on Creates, not Updates
  @foo.update_attributes(params)
else
  # it won't be valid.
end

This may not be the best answer, but it seems to answer your question.

def self.validate_before_update(buyer)#parameters AKA Buyer.validate_before_update(params[:buyer])
# creates temporary buyer which will be filled with parameters
# the temporary buyer is then check to see if valid, if valid returns fail.
      temp_buyer = Buyer.new
# populate temporary buyer object with data from parameters
      temp_buyer.name = buyer["name"]
# fill other required parameters with valid data
      temp_buyer.description = "filler desc"
      temp_buyer.id = 999999 
# if the temp_buyer is not valid with the provided parameters, validation fails
    if  temp_buyer.valid? == false
        temp_buyer.errors.full_messages.each do |msg|
          logger.info msg
        end        
# Return false or temp_buyer.errors depending on your need.
        return false
    end

return true

end

The method update_attributes returns false if object is invalid. So just use this construction

def update
  if @buyer.update_attributes(param[:buyer])
    my_update_database_method
  else
    ...
  end
end

If your my_update_database_method has to be call only before update_attributes, then you shoud use merge way, probably like this:

def update
  @buyer = Buyer.find(params[:id])
  @buyer.merge(params[:buyer])
  if @buyer.valid?
    my_update_database_method
    @buyer.save
  else
    ...
  end
end