Create element in database when we have a reference

[pliant stirrup]

Hi folks,
I have two tables in my database, i created them using "mix phx.gen.json", for the second table i add "user:references:users" to the command.
It create a column "user" links to my users table, a foreign key if correctly understood.

My question is ho to add data to my table ?
When i do a POST request (default create function) with all the parameter (for the user i give the id of the user) it create a line in the table, but my user column is null.
Is there a specific thing to do for adding this type of column ?
Thanks

[gilded pecan]

Can you upload your code?

[abstract frigate]

Check that you definitely have the id in your params
Check that you're casting the user_id in the changeset

[pliant stirrup]

Thanks for your 2 responses, I was writing a complete response with the code and i saw i was just missing :user in the "|> cast(attrs, [:start, :end, :user])". 🤦‍♂️
What the cast really is, i don't understand ?

[gilded pecan]

cast basically lets you do "mass assignment" usually from the POST body etc, and does some data conversion as well for you

so you should be careful because if you cast like that any user making a request can set the user, even if they are not the real user

[pliant stirrup]

Ok, is there a good practice for that ? or just i correctly verify that the user who make the post is the real user

[gilded pecan]

generally don't allow mass assignment/casting of associations or other fields with security implications (like an admin boolean on user)

use put_assoc after you know it's ok

like a user can log in and have their identity attached to the session. you can look up this current_user and pass it to the changeset fn. In the changeset fn you just put_assoc(changeset, :user, current_user)

[abstract frigate]

Or in the cast right? As long as the value is from the server and not client-side

I.e. to put the user_id into params before sending to any of the changeset functions

[gilded pecan]

yes, you could always override it from a "trusted" source. but IMO it's better to provide it as a separate argument or map called trusted that makes it obvious

bugs around this are very scary

[abstract frigate]

Fair enough

[pliant stirrup]

Nice thanks for your complete response, i check that tomorrow !

Ho and do you know good resources to correctly learn elixir ?

[gilded pecan]

did you check out #getting-started ? It's been about 7 years for me so my knowledge is dated 🙂

[abstract frigate]

If it's been 7 years you could be writing resources 😛

[gilded pecan]

i've written a few but yeah 🙂

[abstract frigate]

Ah, good stuff

[pliant stirrup]

Now this is working how can i get my user id back when i get the value ?
The json that is return to me looks like that and don't have the user id. I think it's a type of cast like yesterday but i dont know where to edit the return schema.

{
    "data": {
        "end": "2022-10-26T21:14:09",
        "id": 8,
        "start": "2022-10-26T21:14:09"
    }
}

[abstract frigate]

Where are you getting the data from? Database?

As in are you running Repo.get!/3 on your element and wanting to get back the user_id field?

[pliant stirrup]

Yes from a db, and yes I'm using Repo.get command

[abstract frigate]

What's your code?

I'm assuming it's:

def get_element!(id), do: Repo.get!(Element, id)

If so the user_id should be in the returned values, does your Element schema have a belongs_to :user, User field?

[pliant stirrup]

This is my schema, but i dont have the belong belongs_to :user, User

defmodule Timemanager.WorkingTime.WorkingTimes do
  use Ecto.Schema
  import Ecto.Changeset

  schema "workingtimes" do
    field :end, :naive_datetime
    field :start, :naive_datetime
    field :user, :id

    timestamps()
  end

  @doc false
  def changeset(working_times, attrs) do
    working_times
    |> cast(attrs, [:start, :end, :user])
    |> validate_required([:start, :end, :user])
  end
end

I'm using the get by id and the list all

 def get_working_times!(id), do: Repo.get!(WorkingTimes, id)

 def list_workingtimes do
   Repo.all(WorkingTimes)
 end

[abstract frigate]

Try changing field :user, :id to belongs_to :user, User (remember to alias in the User module) and change the cast and validate_required to take a user_id instead of user

https://hexdocs.pm/ecto/Ecto.Schema.html#belongs_to/3

belongs_to will create a user_id field, which is how I assume you have it stored in the database table

Whenever you're working with FKs use belongs_to , has_many and has_one as they're expected by a bunch of Ecto code, e.g. Changesets, also makes it clearer that it's a FK when you look at your schema