# Sessions

Sessions in Nova are handled by the `nova_session` module. This module is responsible for setting and getting session-values, as well as managing the session data. This means that you can store data in sessions without having to worry about session ids or anything like that - it's all handled for you.

## API

### `nova_session:set/3`

```erlang
-spec set(Req :: cowboy_req:req(), Key :: binary(), Value :: binary()) ->
                 ok | {error, Reason :: atom()} | no_return().
```

This function is used to set a session value. It takes two arguments: the request object, the name of the session-key and the value.

```erlang
nova_session:set(Req, "name", "John Doe").
```

### `nova_session:get/2`

```erlang
-spec get(Req :: cowboy_req:req(), Key :: binary()) ->
          {ok, Value :: binary()} | {error, Reason :: atom()} | no_return().
```

This function is used to get a session value. It takes two arguments: the request object and the name of the session-key.

```erlang
nova_session:get(Req, "name").
```

### `nova_session:delete/2`

```erlang
-spec delete(Req :: cowboy_req:req(), Key :: binary()) -> {ok, Req :: cowboy_req:req()} |
                                                          {error, Reason :: atom()} | no_return().
```

This function is used to delete a value. It takes two arguments: the request object and the name of the value.

```erlang
nova_session:delete(Req, "name").
```

### `nova_session:delete/1`

```erlang
-spec delete(Req :: cowboy_req:req()) -> {ok, Req :: cowboy_req:req()} |
                                           {error, Reason :: atom()} | no_return().
```

This function is used to delete all values. It takes one argument: the request object.

```erlang
nova_session:delete(Req).
```

## Enabling Sessions

Sessions are enabled by default in Nova, but if you need to disable them, you can do so by setting the `use_sessions` configuration option to `false`. This will disable sessions for the entire site.
It's also possible to set the backend for the session data. By default, the session data is stored in an *ETS* table in the Erlang VM but it's quite easy to implement a custom backend.

## Backend

You can implement your own backend by creating a module that implements the `nova_session` behaviour. This behaviour has four functions that need to be implemented: `get_value/2`, `set_value/3`, `delete_value/1` and `delete_value/2`.  
Optionally you can also implement `start_link/0`, which will start a process under nova's supervisor for handling infrastructure of your handler, if it is necessary. For example, in default `nova_session_ets` module it starts a `gen_server` for managing underlying *ETS* table. 

```erlang
-module(my_session_backend).
-behaviour(nova_session).

-export([get_value/2, set_value/3, delete_value/1, delete_value/2]).

get_value(Req, _Key) ->
    %% Your code here,
    {ok, Req}.

set_value(Req, _Key, ) ->
    %% Your code here,
    {ok, Req}.

delete_value(Req) ->
    %% Your code here,
    {ok, Req}.

delete_value(Req, _Key) ->
    %% Your code here,
    {ok, Req}.
```

This module can then be set as the backend in the `sys.config` file under `nova`.

```erlang
{session_manager, my_session_backend}.
```