Question

I have a question about models on Ruby on Rails:

I have this method on Rails that receives a name of the column and the new value for that column:

def change_attribute
    field = params[:field]
    new_value = params[:new_value]
    person = Person.find(params[:id])
    person.update_attribute(field, new_value)
    render :text=>"", :layout=>false
end

But this throws me an error: that field doesn’t exist, I think it should be something like :name, :lastname, etc.

How can I convert my field variable into one of them dinamically to make this function work?

Answer 1

You should be checking whether the field name you get in params[:field] is exactly the same as the original field name (no extra spaces etc.). You can check it by puts params[:field].inspect and checking it in the terminal (where the rails server is started).

According to the docs for update_attribute, we will be able to pass string or symbol as the field name. So, you need not worry about converting the field parameter to symbol before passing it to update_attribute. As you can see the source, here:

def update_attribute(name, value)
  name = name.to_s
  raise ActiveRecordError, "#{name} is marked as readonly" if self.class.readonly_attributes.include?(name)
  send("#{name}=", value)
  save(:validate => false)
end

It is first converted to string and then the setter is called. As @jdoe mentioned, it is not validating the model (see the save(:validate => false) line in code), so you should be aware of that when you are using this method.