A Phoenix library to generate slug for your schema fields

Let's suppose we have a Post schema and we want to generate a slug from title field and save it to the slug field. To achieve that we need to call slugify/2 following the changeset pipeline passing the desireable field. slugify/2 generates the slug and put it to the changeset.

defmodule Post do
  import Slugy, only: [slugify: 2]

  schema "posts" do
    field :title, :string
    field :body, :text
    field :slug, :string
  end

  def changeset(post, attrs) do
    post
    |> cast(attrs, [:title, :body])
    |> slugify(:title)
  end
end

Running this code on iex console you can see the slug generated as a new change to be persisted.

  iex> changeset = Post.changeset(%Post{}, %{title: "A new Post"})
  %Ecto.Changeset{changes: %{title: "A new Post", slug: "a-new-post"}}

slugify/2 just generates a slug if the field's value passed to slugify/2 comes with a new value to persist in attrs (in update cases) or if the struct is a new record to save.

The slugify/2 expects a changeset as a first parameter and an atom on the second one. The function will check if there is a change on the title field and if affirmative generates the slug and assigns to the slug field, otherwise do nothing and just returns the changeset.

iex> slugify(changeset, :title)
%Ecto.Changeset{changes: %{slug: "content-1"}}

In rare cases you need to generate slugs from a field inside a embeded structure that represents a jsonb column on your database.

For example by having a struct like below and we want a slug from data -> title:

%Content{
  type: "text",
  data: %{title: "Content 1", external_id: 1}
}

Just pass a list with the keys following the path down to the desirable field.

  iex> slugify(changeset, [:data, :title])
  %Ecto.Changeset{changes: %{slug: "content-1"}}

If you want a custom slug composed for more than one fields e.g. a post title and the type like so "how-to-use-slugy-video" you need to implement the Slug protocol that extracts the desirable fields to generate the slug.

defmodule Post do
  # ...
end

defimpl Slugy.Slug, for: Post do
  def to_slug(%{title: title, type: type}) do
    "#{title} #{type}"
  end
end

So, %Post{title: "A new Post", body: "Post body", type: "video"} with the above Slug protocol implementation will have a slug like so a-new-post-video

In cases we just want to get the slug string without a changeset involved we can use slugify/1 to achieve that.

iex> slugify("Slugy is awesome")
"slugy-is-awesome"

And lastly for having our routes with the slug we just need to implement the Phoenix.Param protocol to our slugified schemas. Phoenix.Param will extract the slug in place of the :id.

defmodule Post do
  @derive {Phoenix.Param, key: :slug}
  schema "posts" do
  # ...
  end

  def changeset(post, attrs) do
  # ...
  end
end

For more information about Phoenix.Param protocol see in https://hexdocs.pm/phoenix/Phoenix.Param.html

To make sure slug is always unique we can add a unique constraint to our slug column

defmodule MyApp.Migrations.AddSlugToPosts do
  use Ecto.Migration

  def change do
    alter table(:posts) do
      add :slug, :string
    end

    create unique_index(:posts, [:slug])
  end
end

And add the unique_constraint/2 to check in our changeset pipeline.

defmodule Post do
  def changeset(post, attrs) do
    # ...
    |> unique_constraint(:slug)
  end
end

Add to your mix.exs file.

def deps do
  [
    {:slugy, "~> 1.2.1"}
  ]
end

Don’t forget to update your dependencies.

$ mix deps.get

You can also find the docs here https://hexdocs.pm/slugy.

Feel free to contribute to this project. If you have any suggestions or bug reports just open an issue or a PR.