Pollard (pollard v0.1.0)

Tracked, ordered, one-way data transformations for Ecto applications.

Pollard mirrors the Ecto migration system — same conventions, same workflow — but for data, not schema. Transforms are one-way (no rollback), tracked in a database table, and protected by advisory locks to prevent concurrent execution.

Usage

defmodule MyApp.Transforms.BackfillShopDetails do
  use Pollard

  transform "Backfill missing shop details" do
    from(s in "shops", where: is_nil(s.details))
    |> MyApp.Repo.update_all(set: [details: %{}])
  end
end

Each transform block runs in its own database transaction. Multiple blocks per file break work into smaller transactions to avoid holding locks too long.

Running transforms

Via Mix task:

mix pollard.run

Via release module:

Pollard.Runner.run(MyApp.Repo, path)

Summary

Functions

transform(name, list)

Defines a named transform block.

Functions

transform(name, list)

(macro)

Defines a named transform block.

The block runs inside a Repo.transaction/1 call. Each transform in a file gets its own transaction.

transform "Seed resource types" do
  MyApp.Repo.insert_all("resource_types", [
    %{name: "product", inserted_at: DateTime.utc_now()}
  ], on_conflict: :nothing)
end