How does it make sense for an ID not to be found, but for it to be displayed in the loaded information?

Questions / Help
1 
{ok, vote} ->
IO.inspect(vote)

%{
  vote: %App.Votes.Vote{
    __meta__: #Ecto.Schema.Metadata<:loaded, "votes">,
    id: 10,
    value: 1,
    user_id: 2,
    user: #Ecto.Association.NotLoaded<association :user is not loaded>,
    post_id: 6,
    post: #Ecto.Association.NotLoaded<association :post is not loaded>,
    comment_id: nil,
    comment: #Ecto.Association.NotLoaded<association :comment is not loaded>,
    inserted_at: ~N[2023-03-20 18:24:01],
    updated_at: ~N[2023-03-20 18:24:01]
  }
}
[error] GenServer #PID<0.815.0> terminating
** (KeyError) key :id not found in: %{vote: %App.Votes.Vote{__meta__: #Ecto.Schema.Metadata<:loaded, "votes">, id: 10, value: 1, user_id: 2, user: #Ecto.Association.NotLoaded<association :user is not loaded>, post_id: 6, post: #Ecto.Association.NotLoaded<association :post is not loaded>, comment_id: nil, comment: #Ecto.Association.NotLoaded<association :comment is not loaded>, inserted_at: ~N[2023-03-20 18:24:01], updated_at: ~N[2023-03-20 18:24:01]}}

I’m beyond confused currently. Why am I unable to access the ID using vote.id in this situation? I don’t get how the IO.inspect can display the ID and the loaded data can display the ID yet I cannot access it.

2

because id is an attribute of the App.Votes.Vote struct inside the map:

iex(1)> defmodule App.Votes.Vote, do: defstruct [:id]
[..]

iex(2)> vote =  %{vote: %App.Votes.Vote{id: 42}}        
%{vote: %App.Votes.Vote{id: 42}}

iex(3)> vote.vote.id                          
42

hth

1 Like
3

Your vote struct is embedded in a map so you’d get the ID by doing vote.vote.id.

4

Interesting. I realised after I made the post where my issue was, but I’ve always found the wording odd whenever I recieve an error like this and I don’t quite have a full grasp on Elixirs inner workings yet

Thanks for that, it makes it clearer for me in the future when I get issues like this

5

Thank you for this. I’ve had this error in the past as well and the wording always confuses me

6

What’s confusing? The error message is IMO helpful: shows you the data structure that failed to find the field you’re looking for, no?

How would you change the error message?

7

It’s often helpful to grab the data from the error message and put somewhere you can format the output a bit so see what it exactly is.
In your case it could make more obvious that you had a map with a struct inside it.

8

I’m kind of at the just doing things stage of learning so to be honest I wouldn’t have thought the issue was a struct inside a map as thats a bit higher level thinking than I’m capable of currently.

I feel like I can do a lot of things in Elixir and Phoenix, but I’d be lying if I said I actually understood most of what I’ve done at any sort of intelligent level :slight_smile:

I’ve learnt pretty much everything from trial and error + disecting any existing code I can find that seems relevant

9

Consider this:

x = %{
  a: %{
    b: %{
      c: 1
    }
  }
}

You’d get the 1 value by doing x.a.b.c – it’s all a matter of just following parentheses (in this case curly braces). :smiley:

Don’t beat yourself over it, once you are comfortable with the syntax it becomes elementary. It’s only a matter of habit really.

10

This is not updated for Phoenix 1.7 yet but still, check it out: GitHub - tamanugi/realworld-phoenix: Exemplary real world application built with Elixir+Phoenix https://realworld.io

11

Oh I’ve found pretty much everything that exists already in terms of open source projects I think. I’m normally fine with getting values as I have stuff like this in my project already so I can go inception level deep pretty comfortably.

<%= user_notification.notification.current_user.username %>

I’ve never actually thought about or learned about how it is actually working though in terms of maps and structs. I learned how to do it and just did it if that makes sense.

My issue with the error in my original post was that I was returning {:ok, vote} from my query as a case condition, and was trying to access just vote on its own. My query was basically stupid so it messed up how I normally do things. Changed the query to just return vote normally and vote.id worked fine.

2 Likes