Programming Phoenix LiveView:

Community PragProg Customers
,
1

socket is being accessed in the function body, hence the need to include it in the function head.
Current:
def maybe_track_user(

  •     product,*

  •     %{assigns: %{live_action: :show, user_token: user_token}}*

  •     ) do*

  •            if connected?(socket) do*

  •            user = Accounts.get_user_by_session_token(user_token)*

  •            # do tracking here!*
  • end*

Expected:
def maybe_track_user(

  •  product,*

  •  %{assigns: %{live_action: :show, user_token: user_token}} **= socket***

  •  ) do*

  •          if connected?(socket) do*

  •          user = Accounts.get_user_by_session_token(user_token)*

  •         # do tracking here!*

end

Title: Programming Phoenix LiveView: B3.0: Include “=socket” in function header (page 255)
Example: Programming Flutter - ‘pub get’ command not working (page 15)

Please also add the book’s tag if it has not already present, thanks!

2

Thanks for pointing this out! You’ll find the correction in the next Beta release :slight_smile:

3

Programming Phoenix LiveView

Hello,
I am reading my way through the book, Programming Phoenix LiveView, and in chapter 9 (B3.0): Distributed Dashboard, and specifically on the use of Phoenix.Presence; you used a case to check whether the presence has the specified key in its store. However, the case options you use is an empty list and a map.

case Presence.get_by_key(“user_activity”, product.name) do
[] →
Presence.track(
pid,
“user_activity”,
product.name, %{users: [%{email: user.email}]}
)

      %{users: active_users_for_product} ->
                      Presence.update(pid, "user_activity", product.name, %{
                            users: [active_users_for_product | %{email: user.email}]
                      })

end

However, every time I try this, i get “** (CaseClauseError) no case clause matching: %{metas: [%{phx_ref: “FnKY8Tohq2e74wJj”, users: [%{email: “okari@gmail.com”}]}]}”.
Checking it’s documentation also reveals the return type for the function is a map ( presences() ). I might be missing something but I would appreciate your help understanding this, and Presence in general as well as your insights in Phoenix.

Kind regards,
Frankline Okari
okarifrankline5678@gmail.com

4

Hi! Thanks for submitting your question. It does in fact look like there is a mistake in that code! The correct case statement should read like this:

case Presence.get_by_key("user_activity", product.name) do
  [] ->
    Presence.track(
      pid,
      "user_activity",
      product.name, %{users: [%{email: user.email}]}
    )

  %{metas: [%{users: active_users_for_product}]} ->
    Presence.update(pid, "user_activity", product.name, %{
      users: [active_users_for_product | %{email: user.email}]
    })
end

You’ll find that updated in the next Beta release. In the meantime, you can copy in the correction from this comment.