ruby on rails: suddenly failing method

Question

I am not sure how to present my issue best without posting the whole framework. I have a method duplicate! which should duplicate an object (channel). Usually it works but there is one channel where the method fails and I just don't understand why:

def duplicate!
    channel = Channel.new do |c|
      c.title = title << ' (copy)'
      c.description = description
    end
    channel.nodes += nodes
    playlist.nodes.each { |n| channel.playlist.playlist_items.create(node: n) }
    channel
  end

As said nearly all channels duplicate without a problem, but now I have one channel which fails to get duplicated:

2.3.0 :002 > channel.duplicate!
NoMethodError: undefined method `playlist_items' for nil:NilClass
    from /var/www/app/models/channel.rb:110:in `block in duplicate!'
    from /var/www/app/models/channel.rb:110:in `each'
    from /var/www/app/models/channel.rb:110:in `duplicate!'

Every Channel has Nodes and a Playlist, the error producing Channel has too. I don't really understand the error; how can this method fail depended on the object to duplicate?

score 1 · Accepted Answer · edited May 23 '17 at 12:33

1

The reason this is failing is because one of your channels dont have a playlist record. So this line is failing

playlist.nodes.each { |n| channel.playlist.playlist_items.create(node: n) }

for the channel that does not have a playlist record channel.playlist returns nil so when you do channel.playlist.playlist_items you are calling nil.playlist_items, and since nil does not have the method you get an error.

You could just do this instead of making your on duplicate method fyi

 copy_of_channel5 = channel5.dup

This will duplicate the object

You could also do this

copy_of_channel5 = channel5.clone

Look here for a details explanation of the difference between the 2

Trouble Shooting*

Go to your gem file and add this line gem 'pry'
Run bundle
Replace this line playlist.nodes.each { |n| channel.playlist.playlist_items.create(node: n) } with the below code.

playlist.nodes.each {|n| binding.pry}
once the execution console pauses type in the console channel.playlist then press enter and post the output.

edited May 23 '17 at 12:33

Community

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answered Oct 20 '16 at 15:23

C dot StrifeVII

1,885
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Yes, it has a playlist record and that record has nodes in it. – John Alba Oct 20 '16 at 15:30
`2.3.0 :005 > channel.playlist.nodes.count => 8 ` – John Alba Oct 20 '16 at 15:31
You are absolutely certain that every single channel has a playlist record? – C dot StrifeVII Oct 20 '16 at 15:31
are you using pry? – C dot StrifeVII Oct 20 '16 at 15:33
In you console run this `Channel.all.select {|c| c.playlist.nil?}` and tell me what the output is. – C dot StrifeVII Oct 20 '16 at 15:35
no, not using pry. channel is not nil: `2.3.0 :006 > channel.playlist => # ` – John Alba Oct 20 '16 at 15:36
Let me know what the output of that code is, one you run it – C dot StrifeVII Oct 20 '16 at 15:38
`Channel.all.select {|c| c.playlist.nil?} => []` – John Alba Oct 20 '16 at 15:38
Ok that is strange then – C dot StrifeVII Oct 20 '16 at 15:39
Honestly I have no idea why this works at all I don't see where playlist is ever getting created. you are doing this `channel = Channel.new` setting a few values on it then calling `channel.playlist` unless the `playlist` is getting made somewhere else I don't see how this code is not failing all the time. – C dot StrifeVII Oct 20 '16 at 15:45
a Channel `has_one :playlist` and a Playlist `has_many :playlist_items` – John Alba Oct 20 '16 at 15:48
Ok I am going to edit my answer with a section called trouble shoot follow those steps – C dot StrifeVII Oct 20 '16 at 15:50
Since the failing Channel is on a production system, is it possible to bring it into a format I can easily export it to the development system? Since I don't know the difference to working Channels I can not reproduce the error on develop – John Alba Oct 20 '16 at 16:04
Wait so all the out put you showed me from all those commands I gave you were from you local develop environment? – C dot StrifeVII Oct 20 '16 at 16:52
No, these were from production. But a code deploy on production would be less preferable than debugging on develop – John Alba Oct 20 '16 at 16:57
Ok well you can still try the trouble shooting on your local, but I can guarantee you that there is a nil playlist some where and its probably on this line `channel.playlist.playlist_items.create(node: n) }` – C dot StrifeVII Oct 20 '16 at 17:04
I must be missing something here, but thats all I have good luck please update when you find the issue. I know for a fact that the only reason you get that error is because you are calling a method on `nil` so somewhere you are calling `playlist_items` on `nil` . Cheers! – C dot StrifeVII Oct 20 '16 at 17:39
You were right, one Node which should be added as a playlist_item was inconsistent. I don't know where the inconsistency came from but it is solved now. – John Alba Oct 21 '16 at 12:23
Glad I could help – C dot StrifeVII Oct 21 '16 at 12:35

ruby on rails: suddenly failing method

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