# `NoNoncense.MachineId.Strategy.SqlLease`
[🔗](https://github.com/juulSme/NoNoncense/blob/v2.0.0/lib/no_noncense/machine_id/strategy/sql_lease.ex#L2)

Strategy to acquire a machine ID lease from a SQL database (Postgres or MySQL), coordinating
uniqueness across nodes through a single table.

Each machine ID (`0..511`) is a row in the table; a node acquires the lowest available (i.e.
already-expired) row and holds it by keeping its `expires_at` in the future with a random
`token`, renewing it periodically.

Requires a table with one pre-populated row per possible machine ID - see the migration below.

Configure the strategy when starting `NoNoncense.MachineId` and add it after your Repo:

    children = [
      ...
      MyApp.Repo,
      {NoNoncense.MachineId,
       strategy: NoNoncense.MachineId.Strategy.SqlLease,
       strategy_opts: [repo: MyApp.Repo],
       instances: [[base_key: System.fetch_env!("BASE_KEY")]]}
    ]

## Options

  * `:repo` (required) - the `Ecto.Repo` to run queries against
  * `:table` - the table leases are stored in (default `"no_noncense_leases"`)

## Migration

A convenience helper `migrate/1` has been added to this module to help you write a migration. The table name is overridable using option `:table_name`.

    defmodule MyApp.Repo.Migrations.NoNoncenseLeases do
      use Ecto.Migration

      def change, do: NoNoncense.MachineId.Strategy.SqlLease.migrate()
    end

# `migrate_opt`

```elixir
@type migrate_opt() :: {:table_name, String.t()}
```

# `opt`

```elixir
@type opt() :: {:table, String.t()} | {:repo, module()}
```

# `migrate`

```elixir
@spec migrate([migrate_opt()]) :: term()
```

Convenience helper for creating the leases table in an Ecto migration.

Creates table "no_noncense_leases" (overridable) with `id`, `token`, `expires_at` and `lock_version` columns, and preseeds all 512 IDs.

## Options
  - `:table_name` override the name of the leases table. Must be passed to the strategy as well if overridden.

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*Consult [api-reference.md](api-reference.md) for complete listing*