# PostgreSQL adapter for Yggdrasil
[](https://travis-ci.org/gmtprime/yggdrasil_postgres) [](https://hex.pm/packages/yggdrasil_postgres) [](https://hex.pm/packages/yggdrasil_postgres)
This project is a PostgreSQL adapter for `Yggdrasil` publisher/subscriber.
## Small example
The following example uses PostgreSQL adapter to distribute messages:
```elixir
iex(1)> channel = %Yggdrasil.Channel{name: "some_channel", adapter: :postgres}
iex(2)> Yggdrasil.subscribe(channel)
iex(3)> flush()
{:Y_CONNECTED, %Yggdrasil.Channel{(...)}}
```
and to publish a message for the subscribers:
```elixir
iex(4)> Yggdrasil.publish(channel, "message")
iex(5)> flush()
{:Y_EVENT, %Yggdrasil.Channel{(...)}, "message"}
```
When the subscriber wants to stop receiving messages, then it can unsubscribe
from the channel:
```elixir
iex(6)> Yggdrasil.unsubscribe(channel)
iex(7)> flush()
{:Y_DISCONNECTED, %Yggdrasil.Channel{(...)}}
```
## PostgreSQL adapter
The PostgreSQL adapter has the following rules:
* The `adapter` name is identified by the atom `:postgres`.
* The channel `name` must be a string.
* The `transformer` must encode to a string. From the `transformer`s provided
it defaults to `:default`, but `:json` can also be used.
* Any `backend` can be used (by default is `:default`).
The following is an example of a valid channel for both publishers and
subscribers:
```elixir
%Yggdrasil.Channel{
name: "postgres_channel_name",
adapter: :postgres,
transformer: :json
}
```
It will expect valid JSONs from PostgreSQL and it will write valid JSONs in
PostgreSQL.
## PostgreSQL configuration
Uses the list of options for `Postgrex`, but the more relevant optuons are
shown below:
* `hostname` - PostgreSQL hostname (defaults to `"localhost"`).
* `port` - PortgreSQL port (defaults to `5432`).
* `username` - PostgreSQL username (defaults to `"postgres"`).
* `password` - PostgreSQL password (defaults to `"postgres"`).
* `database` - PostgreSQL database (defaults to `"postgres"`).
The following shows a configuration with and without namespace:
```elixir
# Without namespace
config :yggdrasil,
postgres: [hostname: "postgres.zero"]
# With namespace
config :yggdrasil, PostgresOne,
postgres: [
hostname: "postgres.one",
port: 1234
]
```
Also the options can be provided as OS environment variables. The available
variables are:
* `YGGDRASIL_POSTGRES_HOSTNAME` or `<NAMESPACE>_YGGDRASIL_POSTGRES_HOSTNAME`.
* `YGGDRASIL_POSTGRES_USERNAME` or `<NAMESPACE>_YGGDRASIL_POSTGRES_USERNAME`.
* `YGGDRASIL_POSTGRES_PORT` or `<NAMESPACE>_YGGDRASIL_POSTGRES_PORT`.
* `YGGDRASIL_POSTGRES_PASSWORD` or `<NAMESPACE>_YGGDRASIL_POSTGRES_PASSWORD`.
* `YGGDRASIL_POSTGRES_DATABASE` or `<NAMESPACE>_YGGDRASIL_POSTGRES_DATABASE`.
where `<NAMESPACE>` is the snakecase of the namespace chosen e.g. for the
namespace `PostgresTwo`, you would use `POSTGRES_TWO` as namespace in the OS
environment variable.
## Installation
Using this PostgreSQL adapter with `Yggdrasil` is a matter of adding the
available hex package to your `mix.exs` file e.g:
```elixir
def deps do
[{:yggdrasil_postgres, "~> 4.1"}]
end
```
## Running the tests
A `docker-compose.yml` file is provided with the project. If you don't have a
PostgreSQL database, but you do have Docker installed, then just do:
```
$ docker-compose up --build
```
And in another shell run:
```
$ mix deps.get
$ mix test
```
## Relevant projects used
* [`Postgrex`](https://github.com/elixir-ecto/postgrex): PostgreSQL pubsub.
* [`Connection`](https://github.com/fishcakez/connection): wrapper over
`GenServer` to handle connections.
## Author
Alexander de Sousa.
## License
`Yggdrasil` is released under the MIT License. See the LICENSE file for further
details.
