Defines an Arango Edge collection as an Ecto Schema Module.

Edge modules are dynamically created in the environment if they don't already exist. For more on how edge modules are dynamically generated, please read ArangoXEcto.edge_module/3. This will define the required fields of an edge (_from and _to) and will define the default changeset.

Edges utilise Ecto relationships so that the powerful Ecto features can be used. Each Node requires a relationship to be set, either a outgoing/3 or incoming/3. Behind the scenes this creates an Ecto manytomany relationship and generates (or uses the provided) edge module as the intermediary schema. Since the edge collection uses the full _id instead of the _key for the _from and _to fields, once using any of the previously specified relationships a `__idfield will be added to structs that will store the value of the_id` field so that relations can be loaded by Ecto.

extending-edge-schemas

Extending Edge Schemas

If you need to add additional fields to an edge, you can do so by creating your own edge module and defining the required fields as well as any additional fields. Luckily there are some helper macros so you don't have to do this manually again.

When using a custom edge module, it must be passed to the relationship macros in the nodes using the :edge option, read more about these relationships at ArangoXEcto.Schema. Additionally, the :edge option must also be passed to the ArangoXEcto.create_edge/4 function.

A custom schema module must use this module by adding use ArangoXEcto.Edge, from: FromSchema, to: ToSchema.

When defining the fields in your schema, make sure to call edge_fields/1. This will add the _from and _to foreign keys to the schema. It does not have to be before any custom fields but it good convention to do so.

A changeset/2 function is automatically defined on the custom schema module but this must be overridden this so that you can cast and validate the custom fields. The edges_changeset/2 method should be called to automatically implement the casting and validation of the _from and _to fields. It does not have to be before any custom field operations but it good convention to do so.

example

Example

defmodule MyProject.UserPosts do
  use ArangoXEcto.Edge,
      from: User,
      to: Post

  import Ecto.Changeset

  schema "user_posts" do
    edge_fields()

    field(:type, :string)
  end

  def changeset(edge, attrs) do
    edges_changeset(edge, attrs)
    |> cast(attrs, [:type])
    |> validate_required([:type])
  end
end