imranismail / ecto_bitfield

Use bitfields with ecto schemas https://hexdocs.pm/ecto_bitfield/EctoBitfield.html

EctoBitfield

Provides functionality similar to Ruby's bitfields

Motivation

Say you have a user schema that can have one or more of the following service policy [:create_user, :update_user, :delete_user]

To pack that information into a bit we'd do something like this

policies = [create_user: 2^0, update_user: 2^1, delete_user: 2^2]

create_user	update_user	delete_user	BIT
F	F	F	0
T	F	F	1
F	T	F	2
T	T	F	3
F	F	T	4
T	F	T	5
F	T	T	6
T	T	T	7

This saves you a couple of migrations and headache and is also is memory efficient.

Installation

def deps do
  [
    {:ecto_bitfield, "~> 0.1.0"}
  ]
end

Usage

Run a migration to add a bitfield to the schema

alter table(:users) do
  add :policies, :integer, default: 0, null: false
end

Define the Ecto type and use it as the type for the migrated field

defmodule User do
  use Ecto.Schema

  import EctoBitfield

  # takes in a list or a keyword list for explicitly setting the mappings
  defbitfield Policies, [:create_user, :update_user, :delete_user]

  schema "users" do
    field :policies, User.Policies
  end
end

Reading

query = from u in User, where: u.policies == ^[:create_user, :update_user]
#> %Ecto.Queryable{...}

user = Repo.one(query)
#> %User{..., policies: [:create_user, :update_user]}

Writing

changeset = Ecto.Changeset.cast(user, %{policies: [:create_user]}, [:policies])
#> %Ecto.Changeset{..., changes: %{policices: 1}}

Repo.update(changeset)
#> {:ok, %User{..., policices: [:create_user]}}