Decoratex provides an easy way to add calculated data to your Ecto model structs.

• Ecto 2.0 or higher

Maybe you have been in some situations where you need some related data of a model that is not straight stored with it's attributes and it requires a complex logic to calculate their value that can't be solved with a query. Maybe you will need this data in multiple points of the instace life cicle and you want the data available in a standard way instead of using an external module function each time you need it's value.

In this cases, this is what decoratex can do for you:

• Add virtual fields to the model schema to let you use your model like the same model struct with these new fields.

• Provide a function to load data in all or some of these fields whenever you want.

The package can be installed as simply as adding decoratex to your list of dependencies in mix.exs:

  def deps do
    [{:decoratex, "~> 1.1.0"}]
  end

1. Add use Decoratex.Schema to your models.
2. Set the decorate fields inside a block of decorations function.
3. Declare each field with decorate_field name, type, function, options.
   • Name of the virtual field.
   • Type of the virtual field.
   • Function to calculate the value of the virtual field. Always receives a struct model as first param.
   • Default options for the function (arity 2) in case you need to use diferent options in each decoration.
4. Add decorations() inside schema definition.
5. Use Decoratex.decorate function with your model.

defmodule Post do
  use Ecto.Schema
  use Decoratex.Schema

  decorations do
    decorate_field :happy_comments_count, :integer, &PostHelper.count_happy_comments/1
    decorate_field :troll_comments_count, :integer, &PostHelper.count_troll_comments/1
    decorate_field :mention_comments_count, :integer, &PostHelper.count_mention_comments/2, ""
    ...
  end

  schema "posts" do
    has_many :comments, Comment, on_delete: :delete_all

    field :title, :string
    field :body, :string

    timestamps()
    decorations()
  end
end

The decorations definition needs to be placed before schema definition, and then, you should add decorations() inside the schema block. This will automatically add the virtual fields to your model.

Finally, you can use the decorate function of your model module to populate the fields that you need with the function associated to them.

post = Post
|> Repo.get(1)
|> Repo.preload(:comments))

# Decorate all fields
|> Decoratex.decorate

# Decorate one field with an atom
|> Decoratex.decorate(:happy_comments_count)

# Decorate some fields with a list
|> Decoratex.decorate([:happy_comments_count, ...])

# Decorate all fields except one with except key and an atom
|> Decoratex.decorate(except: :happy_comments_count)

# Decorate all fields except some with except key and a list
|> Decoratex.decorate(except: [:happy_comments_count, ...])

post.happy_comments_count
234

When you need to send some options to the decoration functions, you can define a function with arity 2, and set a default value in declaration. The default options value is mandatory for default decorations:

decorate_field :mention_comments_count, :integer, &PostHelper.count_mention_comments/2, ""

Then, you can pass the options value when the struct is decorated

|> Decoratex.decorate(count_mention_comments: user.nickname)

You can use a keyword list for a complex logic, but you need to care about how to manage options in the decoration function (always with arity/2), and the default options in the configurtion.

decorate_field :censured_comments, {:array, Comment}, &PostHelper.censured_comments/2, pattern: "frack", replace: "*"

|> Decoratex.decorate(censured_comments: [pattern: list_of_words, replace: "*"])

And you can mix simple and decorations with options with a list:

|> Decoratex.decorate([:happy_comments_count, censured_comments: [pattern: list_of_words, replace: "*"]])