# as_nested_set
**An [ecto](https://github.com/elixir-lang/ecto) based [Nested set model](https://en.wikipedia.org/wiki/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.
```elixir
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
```elixir
defmodule AsNestedSet.Taxon do
use AsNestedSet, repo: AsNestedSet.TestRepo, scope: [:taxonomy_id]
# ...
end
```
## Options
You can config the name of required field through attributes:
```elixir
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:
```elixir
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
```elixir
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
```elixir
target = Repo.find!(Taxon, 1)
Taxon.remove(target)
```