# EctoBitfield
[](https://travis-ci.org/imranismail/ecto_bitfield)
Provides functionality similar to [Ruby's bitfields](https://github.com/grosser/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
```elixir
def deps do
[
{:ecto_bitfield, "~> 0.1.0"}
]
end
```
## Usage
Run a migration to add a bitfield to the schema
```elixir
alter table(:users) do
add :policies, :integer
end
```
Define the Ecto type and use it as the type for the migrated field
```elixir
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**
```elixir
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**
```elixir
changeset = Ecto.Changeset.cast(user, %{policies: [:create_user]}, [:policies])
#> %Ecto.Changeset{..., changes: %{policices: 1}}
Repo.update(changeset)
#> {:ok, %User{..., policices: [:create_user]}}
```
