Ruby Each Loop Variable Substitution

Question

I'm trying to set all the values to 0 but the 3rd line (send(x)) is giving me problems. Seems right to me, but doesn't work. x is the car and name of the columns in Power. Any tips?

<% @cars.each do |x| %>
  <% @power = Power.find_by_user_id(@user) %>
  <% @power.send(x) = 0 %>
  <% @power.save %>
<% end %>

What do you mean "all the values"? Also this should definitely not be in a view (assuming this is Rails-like). — Andrew Marshall
– Andrew Marshall, Commented Sep 9, 2012 at 16:51
say the @cars array contains c01 c02 c03 etc, and those are the names of the columns — San Backups
– San Backups, Commented Sep 9, 2012 at 16:51
@andrew, yea I'm going to clean this up and take it out of the view, i'm just getting it to work first — San Backups
– San Backups, Commented Sep 9, 2012 at 16:52
If I recall correctly past questions, you tend to set @vars in views, that's not idiomatic, use local variables. And never, ever, a save in a view. — tokland
– tokland, Commented Sep 9, 2012 at 16:52

Andrew Marshall · Accepted Answer · 2012-09-09 16:53:59Z

2

Assuming @cars contains column names of Power, you need to send the setter method (i.e. with an = at the end). You also need to ensure you're passing a symbol to send.

@cars.each do |x|
  @power = Power.find_by_user_id(@user)
  @power.send(:"#{x}=", 0)
  @power.save
end

There's also not an obvious reason why you need to set or save @power in the loop, so it might be better as:

@power = Power.find_by_user_id(@user)
@cars.each do |x|
  @power.send(:"#{x}=", 0)
end
@power.save

answered Sep 9, 2012 at 16:53

Andrew Marshall

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2 Comments

galymzhan Over a year ago

Is it the only way to access dynamic attribute name? Does ActiveRecord class have method like @power.get_attribute_by_name(x)?

Andrew Marshall Over a year ago

@galymzhan There is write_attribute, but that will bypass any custom-defined writer in the model.

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