Contexted

Contexts in Elixir & Phoenix are getting complicated over time. Cross-referencing, big modules and repetitiveness are the most common reasons for this problem.

Contexted arms you with a set of tools to maintain contexts well.

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Note: Official documentation for contexted library is available on hexdocs.

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Table of Contents

• Features
• Installation
• Step by step overview
  • Keep contexts separate
    • Exclude files and folders from check context cross-references
  • Dividing each context into smaller parts
    • Being able to access docs and specs in auto-delegated functions
  • Don't repeat yourself with CRUD operations
• Contributing
• License

Features

• Contexted.Tracer - trace and enforce definite separation between specific context modules.
• Contexted.Delegator - divide the big context module into smaller parts and use delegations to build the final context.
• Contexted.CRUD - auto-generate the most common CRUD operations whenever needed.

Installation

Add the following to your mix.exs file:

defp deps do
  [
    {:contexted, "~> 0.3.2"}
  ]
end

Then run mix deps.get.

Step by step overview

To describe a sample usage of this library, let's assume that your project has three contexts:

• Account
• Subscription
• Blog

Our goal, as the project grows, is to:

1. Keep contexts separate and not create any cross-references. For this to work, we'll raise errors during compilation whenever such a cross-reference happens.
2. Divide each context into smaller parts so that it is easier to maintain. In this case, we'll refer to each of these parts as Subcontext. It's not a new term added to the Phoenix framework but rather a term proposed to emphasize that it's a subset of Context. For this to work, we'll use delegates.
3. Not repeat ourselves with common business logic operations. For this to work, we'll be using CRUD functions generator, since these are the most common.

Keep contexts separate

It's very easy to monitor cross-references between context modules with the contexted library.

First, add contexted as one of the compilers in mix.exs:

def project do
  [
    ...
    compilers: [:contexted] ++ Mix.compilers(),
    ...
  ]
end

Next, define a list of contexts available in the app inside config file:

config :contexted, contexts: [
  # list of context modules goes here, for instance:
  # [App.Account, App.Subscription, App.Blog]
]

And that's it. From now on, whenever you will cross-reference one context with another, you will see an error raised during compilation. Here is an example of such an error:

== Compilation error in file lib/app/accounts.ex ==
** (RuntimeError) You can't reference App.Blog context within App.Accounts context.

Read more about Contexted.Tracer and its options in docs.

Exclude files and folders from cross-references context check

In special cases, you may need to exclude certain folders or files from cross-reference checks due to project structure or naming conventions. To do this, add a list of exclusions in config exclude_paths option:

config :contexted,
  exclude_paths: ["app/test"]

Dividing each context into smaller parts

To divide big Context into smaller Subcontexts, we can use delegate_all/1 macro from Contexted.Delegator module.

Let's assume that the Account context has User, UserToken and Admin resources. Here is how we can split the context module:

# Users subcontext

defmodule App.Account.Users do
  def get_user(id) do
    ...
  end
end

# UserTokens subcontext

defmodule App.Account.UserTokens do
  def get_user_token(id) do
    ...
  end
end

# Admins subcontext

defmodule App.Account.Admins do
  def get_admin(id) do
    ...
  end
end

# Account context

defmodule App.Account do
  import Contexted.Delegator

  delegate_all App.Account.Users
  delegate_all App.Account.UserTokens
  delegate_all App.Account.Admins
end

From now on, you can treat the Account context module as the API for the "outside" world.

Instead of calling:

App.Account.Users.find_user(1)

You will simply do:

App.Account.find_user(1)

Being able to access docs and specs in auto-delegated functions

Both docs and specs are attached as metadata of module once it's compiled and saved as .beam. In reference to the example of App.Account context, it's possible that App.Account.Users will not be saved in .beam file before the delegate_all macro is executed. Therefore, first, all of the modules have to be compiled, and saved to .beam and only then we can create @doc and @spec of each delegated function.

As a workaround, in Contexted.Tracer.after_compiler/1 all of the contexts .beam files are first deleted and then recompiled. This is an opt-in functionality, as it extends compilation time. If you want to enable it, set the following config value:

config :contexted,
  enable_recompilation: true

You may also want to enable it only for certain environments, like dev.

Please also note that when this functionality is enabled, during the recompilation process, warnings are temporarily silenced to avoid logging conflict warnings. It will still log warnings as intended, during the first compilation, therefore it won't have any affect on normal compilation flow.

Read more about Contexted.Delegator and its options in docs.

Don't repeat yourself with CRUD operations

In most web apps CRUD operations are very common. Most of these, have the same pattern. Why not autogenerate them?

Here is how you can generate common CRUD operations for App.Account.Users:

defmodule App.Account.Users do
  use Contexted.CRUD,
    repo: App.Repo,
    schema: App.Accounts.User
end

This will generate the following functions:

iex> App.Accounts.Users.__info__(:functions)
[
  change_user: 1,
  change_user: 2,
  create_user: 0,
  create_user: 1,
  create_user!: 0,
  create_user!: 1,
  delete_user: 1,
  delete_user!: 1,
  get_user: 1,
  get_user!: 1,
  list_users: 0,
  update_user: 1,
  update_user: 2,
  update_user!: 1,
  update_user!: 2
]

Read more about Contexted.CRUD and its options in docs.

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

License

Curiosum

Distributed under the MIT License. See LICENSE for more information.