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All Things Elixir @ Surge Ventures Inc, the creators of Fresha
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lib/surgex/data_pipe/foreign_data_wrapper.ex
defmodule Surgex.DataPipe.ForeignDataWrapper do
@moduledoc """
Configures a PostgreSQL Foreign Data Wrapper linkage between two repos.
Specifically, it executes the following steps:
- adds postgres_fdw extension to local repo
- (re)creates server and user mapping based on current remote repo's config
- copies remote repo's schema to local repo (named with underscored repo module name)
Everything is executed in one transaction, so it's safe to use while existing transactions that
depend on connection to foreign repo and its schema are running in the system (based on
https://robots.thoughtbot.com/postgres-foreign-data-wrapper).
## Usage
Refer to `Surgex.DataPipe` for a complete data pipe example.
"""
require Logger
alias Ecto.Adapters.SQL
@doc """
Links source repo to a given foreign repo.
"""
def init(source_repo, foreign_repo) do
local_name = source_repo |> Module.split |> List.last
server = schema = build_foreign_alias(foreign_repo)
config = foreign_repo.config
Logger.info(fn -> "Preparing foreign data wrapper at #{local_name}.#{server}..." end)
server_opts = build_server_opts(config)
user_opts = build_user_opts(config)
script = [
"CREATE EXTENSION IF NOT EXISTS postgres_fdw",
"DROP SERVER IF EXISTS #{server} CASCADE",
"CREATE SERVER #{server} FOREIGN DATA WRAPPER postgres_fdw" <> server_opts,
"CREATE USER MAPPING FOR CURRENT_USER SERVER #{server}" <> user_opts,
"DROP SCHEMA IF EXISTS #{schema}",
"CREATE SCHEMA #{schema}",
"IMPORT FOREIGN SCHEMA public FROM SERVER #{server} INTO #{schema}"
]
{:ok, _} = apply(source_repo, :transaction, [fn ->
Enum.each(script, fn command ->
SQL.query!(source_repo, command)
end)
end])
end
@doc """
Puts a foreign repo prefix (aka. schema) in a given Repo query.
After calling this function, a given query will target tables from the previously linked repo
instead of Repo.
"""
def prefix(query = %{}, foreign_repo) do
Map.put(query, :prefix, build_foreign_alias(foreign_repo))
end
def prefix(schema, foreign_repo) do
import Ecto.Query, only: [from: 1]
prefix(from(schema), foreign_repo)
end
defp build_server_opts(config) do
build_opts([
{"host", Keyword.get(config, :hostname)},
{"dbname", Keyword.get(config, :database)},
{"port", Keyword.get(config, :port)}
])
end
defp build_user_opts(config) do
build_opts([
{"user", Keyword.get(config, :username)},
{"password", Keyword.get(config, :password)}
])
end
defp build_opts(mapping) do
opts_string =
mapping
|> Enum.filter(fn {_, value} -> value end)
|> Enum.map(fn {option, value} -> "#{option} '#{value}'" end)
|> Enum.join(", ")
case opts_string do
"" -> ""
_ -> " OPTIONS (#{opts_string})"
end
end
defp build_foreign_alias(repo) do
repo
|> Module.split
|> List.last
|> Macro.underscore
end
end