as_nested_set

An ecto based Nested set model implementation for database

Installation

Add as_nested_set to your list of dependencies in mix.exs:

  def deps do
    [{:as_nested_set, github: "https://github.com/secretworry/as_nested_set.git"}]
  end

Usage

To make use of as_nested_set your model has to have at least 4 fields: id, lft, rgt and parent_id. The name of those fields are configurable.

defmodule AsNestedSet.TestRepo.Migrations.MigrateAll do
  use Ecto.Migration

  def change do
    create table(:taxons) do
      add :name, :string
      add :taxonomy_id, :id
      add :parent_id, :id
      add :lft, :integer
      add :rgt, :integer

      timestamps
    end

  end
end

Enable the nested set functionality by use AsNestedSet on your model

defmodule AsNestedSet.Taxon do
  use AsNestedSet, repo: AsNestedSet.TestRepo, scope: [:taxonomy_id]
  # ...
end

Options

You can config the name of required field through attributes:

defmodule AsNestedSet.Taxon do
  @right_column :right
  @left_column :left
  @node_id_column :node_id
  @parent_id_column :pid
  # ...
end

• @right_column: column name for right boundary(default to lft, since left is a reserved keyword for Mysql)
• @left_column: column name for left boundary(default to rgt, reserved too)
• @node_id_column: specifies the name for the node id column(default to id, i.e. the id of the model, change this if you want to has a different id, or you id field is different)
• @parent_id_column: specifies the name for the parent id column(default to parent_id)

You can also pass following to modify its behavior:

defmodule AsNestedSet.Taxon do
  use AsNestedSet, repo: AsNestedSet.TestRepo, scope: [:taxonomy_id]
  # ...
end

• scope: (required) a list of column names which restrict what is to be considered within the same tree(same scope).
• repo: (required) the name of the repo to operate on

Model Operations

Once you have set up you model, you can then

Add a new node

target = Repo.find!(Taxon, 1)
# add to left
Taxon.add(target, %Taxon{name: "left", taxonomy_id: 1}, :left)
# add to right
Taxon.add(target, %Taxon{name: "right", taxonomy_id: 1}, :right)
# add as first child
Taxon.add(target, %Taxon{name: "child", taxonomy_id: 1}, :child)

# add as root
Taxon.add(%Taxon{name: "root", taxonomy_id: 1}, :root)

Remove a specified node and all its descendants

target = Repo.find!(Taxon, 1)
Taxon.remove(target)