# DawdleDB
DawdleDB uses Dawdle and SQS to capture change notifications from PostgreSQL.
## Installation
The package can be installed by adding `dawdle_db` to your list of
dependencies in `mix.exs`:
```elixir
def deps do
[
{:dawdle_db, "~> 0.5.0"}
]
end
```
Documentation can be found at [https://hexdocs.pm/dawdle_db](https://hexdocs.pm/dawdle_db).
## Usage
DawdleDB can be run in either watcher mode or listener mode. In watcher mode it
captures PostgreSQL notifications and encodes them into an Elixir struct which
is then posted to SQS. In listener mode, the events are pulled out of SQS and
handed off to handlers for processing.
For best results, there should only be one instance of DawdleDB running in
watcher mode; though you can have many instances running in listener mode.
### Initial setup
DawdleDB relies on database triggers to fire the appropriate notifications.
There are helpers defined in `DawdleDB.Migration` to simplify initial setup
and defining the triggers.
For example, if you already have a `users` table and you wish to recieve
notifications on insert, update, and delete, you could create a migration like
the following:
```
defmodule MyApp.DawdleDBSetup do
use Ecto.Migration
import DawdleDB.Migration
def up do
create_watcher_events_table()
update_notify("users", [:insert, :update, :delete])
end
def down do
remove_notify("users", [:insert, :update, :delete])
drop_watcher_events_table()
end
end
```
### Handlers
Once the watcher events table has been created, and triggers have been setup,
define a handler based on `DawdleDB.Handler`.
```
defmodule MyApp.UserHandler do
use DawdleDB.Handler, type: MyApp.User
alias MyApp.User
def handle_insert(%User{} = new) do
# Do something when a user is created
:ok
end
def handle_update(%User{} = new, %User{} = old) do
# Do something when a user is updated
:ok
end
def handle_delete(%User{} = old) do
# Do something when a user is deleted
:ok
end
end
```