Ecto association has_one find or create

Questions / Help
1

Hi,

I have a post and meta_data table. A post has one meta_data.

In my application, when I click the create post button, a post is created and saved to the database. However, the meta data is not. It is done from the frontend using a graphql query.

I have this changeset in the post schema:

 def changeset(post, attrs) do
    post
    |> cast(attrs, [])
    |> cast_assoc(:meta_data)
  end

When I pass the meta data in, I have all the attributes except for the ID (as it isn’t guaranteed to exist). When I invoke this changeset with the following params:

%{"id" => 6, "meta_data" => %{"description" => "test", "keywords" => "test", "title" => "test"}}

I get this error message: you are attempting to change relation :meta_data.... I understand why, it is because it is looking for a meta_data. My update post method is as follows:

def update_post(attrs \\ %{}) do
    post = get_post_for_update!(attrs.id)
    Post.changeset(post, attrs)
    |> Repo.update()
  end

Is there a way in ecto, to find or create an association in an update changeset?

2

So you never want to overwrite the metadata if it already exists?

1 Like
3

yep that is correct