gnomon for Elixir

Branches of a PostgreSQL database with gnomon from Postgrex and Ecto, and an ExUnit case that gives each test its own scratch branch in place of the SQL sandbox.

# Postgrex: sessions that start on a branch (startup parameters)
Postgrex.start_link(Gnomon.connect_opts([database: "app"], "feature"))       # c_module: true with the C module

# or each new connection on a branch
Postgrex.start_link(database: "app", after_connect: {Gnomon, :use, ["feature"]})

# Ecto: the repo's pool on a branch, queries prefixed with the routing schema
config :my_app, MyApp.Repo, Gnomon.Ecto.repo_config([database: "app"], "feature")
def default_options(_op), do: [prefix: Gnomon.Ecto.prefix()]                 # in MyApp.Repo

# one transaction on a branch (behind pgbouncer in transaction mode)
Gnomon.with_branch(MyApp.Repo, "feature", fn repo -> repo.insert!(%Order{}) end)

# errors: the stable slug
rescue e in Postgrex.Error -> Gnomon.code(e)                                  # "ddl_on_branch"

Gnomon.connection_options(conn, branch) returns what the database computes for a branch (its schema version and mask included), for tools that take libpq options.

ExUnit

defmodule MyApp.SignupTest do
  use Gnomon.Case, repo: MyApp.Repo        # or connect: fn -> Postgrex.start_link(...) end
  test "signup", %{repo: repo, branch: branch} do
    repo.insert!(%User{email: "a@example.com"})   # committed, on the test's own branch
  end
end

With repo:, the test checks a connection out of the sandbox pool without the sandbox's transaction, so the code under test may commit and use transactions of its own. The repo's pool must be Ecto.Adapters.SQL.Sandbox as for the sandbox. Each branch is dropped when its test ends (GNOMON_KEEP=1 keeps them).

Tests

./test.sh runs the tests with a fake query module: no Postgrex, Ecto or database is needed.

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