How to perform an upsert without loading associations?

Questions / Help
1

Assume an Author schema:

schema "authors" do
    field :name, :string
    has_many :posts, Post
  end

  def changeset(struct, attrs) do
    struct
    |> cast(attrs, [:name])
  end

I can perform an update:

author |> Author.changeset(%{name: "Jo"}) |> Blog.Repo.update!()

but an upsert fails:

 author |> Author.changeset(%{name: "Jo"}) |> Blog.Repo.insert!(on_conflict: {:replace_all_except, [:id]})
** (RuntimeError) attempting to cast or change association `posts` from `Author` that was not loaded. Please preload your associations before manipulating them through changesets

Is it possible to perform an upsert without loading the associations?
Or is this by design?

2

Have you taken a look at Repo.insert_all/3? They have a full section on upsert, maybe that helps.

Something like

query = Author |> where([a], a.id == ^id) |> select([a], %{name: "Jo"})
Repo.insert_all(Author, query, on_conflict: : replace_all)
3

Maybe Repo.insert_or_update is what you’re looking for. A changeset is already aware if you loaded author from the db or not.

4

The code that implements replace_all_except starts from the schema’s list of fields:

And that’s a list of built from all the field calls inside the schema block - associations aren’t in there.

Can you post the stacktrace of the error and/or the full source of Author.changeset/2?

5

Thanks for all the feedback. Along with a discussion on the Elxir discord I’ve improved my understanding of how upsert works.

What I should be doing is this:

%Author{} |> Author.changeset(%{name: "Jo"}) |> Blog.Repo.insert!(on_conflict: {:replace_all_except, [:id]})

If the struct metadata state is built then it works fine. If it’s loaded then the associations are expected.

I want to avoid loading it first, and just insert or update an existing record, so using a built struct is the best approach.

If I had the struct already loaded I can use insert_or_update