Saving an association from a select input

Hello !

You’re using inputs_for, which is made to create / update embedded schema or relationship. When you declare belongs_to, session his a direct link to the related schema, but it’s not the field available on the students table. That macro automatically adds the foreign key, which by default would be session_id.

So in your case, you need to remove the inputs_for, and replace with the normal select, pointing to session_id, like this (actually, has stated by @antoine, you have changed the foreign_key to bold_session, so that should be the one to use here ):

<%= label sf, :bold_session %>
<%= select sf, :bold_session, @sessions, prompt: "Choose a session" %>
<%= error_tag sf, :bold_session %>

Normally, it should then just apply the selection to the proper column and create the student with the relationship assigned.

Thanks @shd42, indeed the select is more appropriate, didn’t know this, I have never used forms.

So if you change your view to use the select instead of the input, you will receive an attrs that looks like this

%{
    ...
    "session_id" => 5,
    ...
}

Then you simply have to cast it

  @fields [:firstname, :lastname, :session_id]
  @required_fields [:firstname, :lastname, :session_id]

  def changeset(student, attrs) do
    student
    |> cast(attrs, @fields)
    |> validate_required(@required_fields)
  end

But this is true only if the foreign_key name in your table is named session_id.

Wich seems to not to be the case, because you overrided it:

  belongs_to :session, Session, foreign_key: :bold_session

Any reason for this ? what was the intention ?

If you need this field ne be named bold_session, just change session_id to bold_session in both changeset and your view.

I think the other members have already adressed your concern.

I just want to comment on a little detail.

To follow the usual association naming (of course this is not mandatory ^^) I would suggest to rename the has_many name to a plural form such as students instead of student. I think it is more readable.

Ex:

has_many :things, Thing
has_many :criteria, Criterion
has_one :profile, Profile

Thanks for the feedback. I actually created a column called bold_session to hold the ID in the DB. I did this because I didn’t know the convention. I think I’ll go back and change the structure, as convention makes more sense and I don’t want to go down the rabbit hole of overriding everything.

Also, I was trying to cast_assoc on this, so thanks for the callout!

Completely agree - It felt wrong when I was typing out the question. Thanks for the feedback!

This makes a lot more sense. I wasn’t understanding exactly how inputs_for and the associations were working. Thanks for the explanation. It really helped clear things up for me.