A mix task for generating an ERD (Entity Relationship Diagram) in various formats for all Ecto schemas available in your project.

Supported formats:

• DOT (default)
• PlantUML
• DBML
• QuickDBD
• Mermaid

defmodule Blog.Post do
  use Ecto.Schema

  schema "posts" do
    field(:title, :string)
    field(:text, :string)
    timestamps()
    belongs_to(:user, Blog.User)
    has_many(:comments, Blog.Comment)
  end
end

defmodule Blog.Comment do
  use Ecto.Schema

  schema "comments" do
    field(:text, :string)
    timestamps()
    belongs_to(:post, Blog.Post)
    belongs_to(:user, Blog.User)
  end
end

defmodule Blog.User do
  use Ecto.Schema

  schema "users" do
    field(:email, :string)
    has_many(:posts, Blog.Post)
    has_many(:comments, Blog.Comment)
  end
end

The package can be installed by adding ecto_erd to your list of dependencies in mix.exs:

def deps do
  [
    {:ecto_erd, "~> 0.6", only: :dev}
  ]
end

Just run:

mix ecto.gen.erd

The command above produces a file in DOT format which can be converted to an image using graphviz utility:

dot -Tpng ecto_erd.dot -o erd.png

Configuration is possible via .ecto_erd.exs file. The docs can be found at https://hexdocs.pm/ecto_erd. Configuration examples and output for a couple of open-source projects can be found in EXAMPLES group of PAGES section.

Trying to run ecto_erd on an umbrella project? Did you get this error?

$ mix ecto.gen.erd
** (RuntimeError) Unable to detect `:otp_app`, please specify it explicitly

The easiest solution is to run the command on one of the apps in the apps/ directory. Another option is to create a configuration file and specify the :otp_app. See the docs for details.