Returns a specification to start this module under a supervisor.

See Supervisor.

Callback implementation for Supervisor.init/1.

@spec subscribe(identifier(), term()) :: :ok | {:error, term()}

Subscribe to notifications from watchers.

Examples:

iex> EctoWatch.subscribe({Comment, :updated})

When subscribing to a watcher with the label option specified as :comment_updated_custom:

iex> EctoWatch.subscribe(:comment_updated_custom)

You can subscribe to notifications just from specific primary key values:

iex> EctoWatch.subscribe({Comment, :updated}, user_id)

Or you can subscribe to notifications just from a specific foreign column (**the column must be in the watcher's extra_columns list):

iex> EctoWatch.subscribe({Comment, :updated}, {:post_id, post_id})