Defimpl Phoenix.Param to override to_param causes (FunctionClauseError) no function clause matching in Phoenix.Param.Rumbl.Video.to_param/1

while trying to follow the examples in Programming Phoenix (book) release P1.0,

everything is working fine until Page 167 when instructed to add the lines:

defimpl Phoenix.Param, for: Rumbl.Video do
  def to_param(%{slug: slug, id: id}) do

to: rumbl/web/models/video.ex

Before I add the lines, the tests pass (as expected):

But once the defimpl is added the tests fail:

The error message for two of the failing tests is:

** (FunctionClauseError) no function clause matching in Phoenix.Param.Rumbl.Video.to_param/1

Stack trace:

Code Snapshot when these 5 lines were added:

Any help with understanding this would be much appreciated!

Note: I’ve tried googling (for a while) …

I’ve read through dozens of similar-looking questions on SO &

but none were helpful. it appears I’m the only one seeing this error!

Posting a StackOverflow question is my “last resort” before giving up programming! :frowning:

On the “Programming Phoenix” book’s errata page: there is another person reporting an issue with the same code but their error is different …

Also posted on StackOverflow just in case:

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If we look at the error, it doesn’t seem that your Video struct has the slug field. Are you sure it is there?

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Thanks for quick rely @josevalim, you’re correct! (it’s PEBKAC…) :confused:
adding the field :slug, :string Fixed it. :blush:
case closed :white_check_mark:

Thankfully this won’t be an issue for much longer once Models are gone in 1.3… :wink:
Obrigado José! :thumbsup:

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