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jake
@jakeprem.com
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jakeprem.com
Schemas in your app with attachments add a single foreign key to the ledger table per attachment type. e.g. a Post schema could have `cover_image_ledger_id` and `files_ledger_id`. Then any attachments you add have a foreign key to the ledger table as well.
September 24, 2025 at 6:09 PM
jakeprem.com
The more conventional approach of `has_many, through:`:

1. Maintains database integrity with foreign keys
2. `Repo.preload(posts, :photos)` includes a query of the ledger table as well as the attachments table
3. `:through` associations are read only
Ecto code showing a more conventional has many through approach: schema "posts" do belongs_to :photos_ledger, AttachmentLedger has_many :photos, through: [:photos_ledger, :attachments] end
February 19, 2025 at 6:19 PM
jakeprem.com
Pros of this approach:

1. Both fields still use a foreign key reference in the database
2. `Repo.preload(posts, :photos)` queries the attachments table directly rather than traversing the ledger table.
3. `Ecto.build_assoc/3` and related seem to work.
An example Ecto migration showing that both fields still use foreign key references: create table(:attachments) do # ... add :attachment_ledger_id, references(:attachment_ledgers) end create table(:posts) do # ... add :photos_ledger_id, references(:attachment_ledgers) end
February 19, 2025 at 6:19 PM
jakeprem.com
Experimenting with building a library with ActiveStorage-like functionality for Ecto.

Convince me this `has_many` usage is a bad idea?

#ElixirLang
Elixir code describing an approach to has_many associations in Ecto using a ledger record: schema "posts" do belongs_to :photos_ledger, AttachmentLedger has_many :photos, Attachment, foreign_key: :attachment_ledger_id, references: :photos_ledger_id end iex> post = %Post{photos_ledger_id: 1} iex> Ecto.build_assoc(post, :photos, attrs) %Attachment{attachment_ledger_id: 1}
February 19, 2025 at 6:19 PM