Settings View Source Building files from EEx templates

EEx templates can be used to create files in Ejected Apps that don't exist in the Base Project.

an-example-scenario

An Example Scenario

Imagine you do not use runtime configuration in your Base Project, but you want a config/runtime.exs in your ejected apps.

Furthermore, imagine the contents of runtime.exs need to be wildly different between apps based on the Lib and Mix Dependencies of the app.

This is an ideal scenario for using an EEx template. Below are the steps to create runtime.exs with an EEx template.

step-1-set-the-template-directory-in-your-blueprint-module

Step 1: Set the template directory in your Blueprint module

defmodule MyApp.Uniform.Blueprint do
  use Uniform.Blueprint, templates: "lib/uniform/templates"

step-2-add-the-eex-file-in-the-correct-relative-path

Step 2: Add the EEx file in the correct relative path

EEx templates must be added in the destination path, relative to the templates directory from use Uniform.Blueprint, with a .eex suffix.

So to emit our file into config/runtime.exs, we must create it in

lib/uniform/templates/config/runtime.exs.eex
\___________________/ \________________/\__/
        |                     |           |
templates directory     destination    .eex suffix (Don't forget!)

step-3-write-the-template

Step 3: Write the template

Here is an example of what the runtime.exs.eex template might contain.

Note the use of Eject Fences at the end of the file.

import Config

<%= if MyApp.Uniform.Blueprint.deploys_to_fly_io?(app) do %>
  config :my_base_app, some_api_token: System.get_env("SOME_API_TOKEN")
<% end %>

config :my_base_app, MyBaseAppWeb.Endpoint,
  url: [
    host: System.get_env("HOST"),
    port: String.to_integer(System.get_env("EXTERNAL_PORT"))
  ],
  secret_key_base: System.get_env("SECRET_KEY_BASE")

config :my_base_app, MyBaseApp.Repo,
  priv: "priv/my_base_app_repo",
  url: System.get_env("DATABASE_URL")

# uniform:app:some_app
config :my_base_app, some_configuration: "just for some_app"
# /uniform:app:some_app

Keep in mind a few considerations documented below when building out templates.

the-app-struct

The App struct

In EEx templates, the Uniform.App struct will be available as app. You can use the contents of app.extra to make decisions about what to render in the template.

Also, the Uniform.App.depends_on?/3 utility is available as depends_on? and can be used like this.

depends_on?(app, :mix, :absinthe)

code-transformations

Code transformations

Code Transformations are ran after the template is generated. This means that you can inject the base app name into a template anywhere you want the ejected app name to appear, and it will be transformed into the ejected app name.

So in the example above, instead of writing

config :<%= app.name.underscore %>

We just wrote

config :my_base_app