Adding a Nova app to your application#

We have talked about views, we have touched controllers and we have talked about routing.

Now we will introduce how we can use someone else nova application inside yours. We will use Nova Admin as an example. This is a nova application that lets you do observer kind of functionality.

Adding the dependency#

In our nova application we open rebar.config and add Nova admin as a dependency.

{deps, [
        nova,
        {flatlog, "0.1.2"}, %% Used for logging - Change if needed
        {nova_admin, ".*", {git, "git@github.com:novaframework/nova_admin.git", {branch, "master"}}}
       ]}.

Configuring the sub-application#

Now we need to tell Nova about this new application. We do this in our dev_sys.config.src file. Nova has a configuration called nova_apps that we set in our own application’s environment. This tells Nova to compile and mount routes from other Nova applications.

{my_first_nova, [
    {nova_apps, [
        {nova_admin, #{prefix => "/admin"}}
    ]}
]}

The prefix option means all routes from nova_admin will be mounted under /admin. So if nova_admin has a route for / it will be available at /admin/ in our application.

Your full dev_sys.config.src should now look something like this:

[
  {kernel, [
    {logger_level, debug},
    {logger, [
      {handler, default, logger_std_h,
        #{formatter => {flatlog, #{
            map_depth => 3,
            term_depth => 50,
            colored => true,
            template => [colored_start, "[\033[1m", level, "\033[0m", colored_start, "] ", msg, "\n", colored_end]
          }}}}
    ]}
  ]},
  {nova, [
         {use_stacktrace, true},
         {environment, dev},
         {cowboy_configuration, #{
                                  port => 8080
                                 }},
         {dev_mode, true},
         {bootstrap_application, my_first_nova},
         {plugins, [
                    {pre_request, nova_request_plugin, #{read_urlencoded_body => true}}
                   ]}
        ]},
  {my_first_nova, [
      {nova_apps, [
          {nova_admin, #{prefix => "/admin"}}
      ]}
  ]}
].

How it works#

When Nova starts up it reads the bootstrap_application setting and looks for the nova_apps configuration in that application’s environment. It then compiles routes from all listed sub-applications and merges them into the routing tree.

Each sub-application is a standalone Nova app with its own router module. Nova Admin has a nova_admin_router.erl that defines its own routes. When we set prefix => "/admin", Nova prepends that prefix to all of nova_admin’s routes.

Starting it up#

Now we can fetch dependencies and start the node:

$ rebar3 nova serve

If we check our routes we should see nova_admin’s routes mounted under /admin:

$ rebar3 nova routes

You can now go to localhost:8080/admin in your browser and you should see the Nova Admin interface. It gives you observer-like functionality directly in the browser, you can see running processes, memory usage and other information about your running Erlang node.

Using other Nova apps#

The same pattern works for any Nova application. If you find or build a Nova app that you want to include, you just:

1. Add it as a dependency in rebar.config
2. Add it to nova_apps in your sys.config with an optional prefix
3. Start your application

You can mount multiple sub-applications, each with their own prefix:

{my_first_nova, [
    {nova_apps, [
        {nova_admin, #{prefix => "/admin"}},
        {my_api_app, #{prefix => "/api"}}
    ]}
]}

This is one of the powerful features of Nova. You can compose applications from multiple Nova apps, each handling their own piece of the system. In the next article we will look at how to build a JSON API with Nova.