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DataMapper plugin enabling easy creation of tree structures from your DM models.
This requires a foreign key property for your model, which by default would be called :parent_id.
Install the dm-is-tree gem.
$ (sudo)? gem install dm-is-tree
Download or clone dm-is-versioned from Github.
$ cd /path/to/dm-is-tree $ rake install # will install dm-is-tree
To start using this gem, just...
require 'dm-is-tree'
Lets say we have a Category model...
class Category include DataMapper::Resource property :id, Serial property :name, String end
...and we want to have a tree structure within it, something like this:
the_parent
+- child
+- grandchild1
+- grandchild2
To achieve this we just add the following to the model:
class Category <snip...> is :tree, :order => :name end # No need to define the :parent_id property, it will be added automatically property :parent_id, Integer
This will automatically add the following to your model:
#parent / #parent=
#children / #children=
#siblings
#generation
#ancestors
also aliased as #self_and_siblings for those used to AR's :acts_as_tree
#root
also aliased as #first_root for those used to AR's :acts_as_tree
#first_root
#roots
Before we go onto the usage examples, a few quick words about configuration options available:
Specifies the column name to use for tracking of the tree (default: #parent_id).
class Category <snip...> is :tree, :child_key => :some_other_foreign_key_id end
Specifies the name of the Model to use for the tree (default: Model class name defined in)
class Category <snip...> is :tree, :model => 'SomeStrangeModelName' end
Specifies the sort order of the children when retrieving them (default: not present)
class Category <snip...> is :tree, :order => [:updated_at, :name] end
To create the above structure, we would start with:
the_parent = Category.create(:name => "the_parent")
The #parent instance method returns the node referenced by the foreign key - :parent_id or the defined :child_key.
# by default #parent and #parent_id return nil when there is no parent the_parent.parent # => nil
The #parent= instance method sets the :parent_id foreign key to the parent's id attribute value.
To define a parent you can use either of these syntaxes:
a_child = Category.create(:name => "a_child", :parent => the_parent) a_child = Category.create(:name => "a_child", :parent_id => the_parent.id) a_child = Category.create(:name => "a_child") a_child.parent = the_parent
When retrieving the parent, you will receive the full parent object ( or nil if none was declared )
a_child.parent # => the_parent
The #children instance method returns all nodes with the current node as their parent, in the order specified by the :order configuration option.
# by default #children return an empty Array when there are no children a_child.children # => [] # or an Array with child objects when there are children the_parent.children # => [a_child]
The #children= instance method adds children by setting the :parent_id foreign key to the parent's id attribute value.
To add a child you can use either of these syntaxes:
child = the_parent.children.create(:name => "child") grandchild1 = Category.create(:name => "grandchild1") child.children << grandchild1 grandchild2 = child.children.create(:name => "grandchild2")
When retrieving children, or a child, you will receive an Array of child objects.
child.children # => [grandchild1, grandchild2,...] # just retrieve the first child child.children.first # => grandchild1
The #siblings instance method returns all the children of the parent, excluding the current node.
# by default #siblings return an empty Array when there are no siblings the_parent.siblings # => [] grandchild1.siblings # => [grandchild2]
The #generation instance method returns all the children of the parent, including the current node.
# by default #generation return an Array with itself only when it's a 'lonely child' the_parent.generation # => [the_parent] # grandchild1.generation # => [grandchild1, grandchild2]
The #ancestors instance method returns all the ancestors of the current node.
# by default it returns an empty Array when born through immaculate conception (is root) the_parent.ancestors # => [] grandchild2.ancestors # => [the_parent, a_child]
The #root instance method returns the root (parent) of the current node.
# by default returns itself only when it's the root node the_parent.root # => the_parent a_child.root # => the_parent grandchild2.root # => the_parent
The #first_root class method returns the first root declared in the model.
Category.first_root # => the_parent
The #roots class method returns an Array of the roots declared in the model.
Category.roots # => [the_parent] parent2 = Category.create(:name => 'parent2') Category.roots # => [the_parent, parent2]
parent = Category.create(:name => "parent") child = parent.children.create(:name => "child") grandchild1 = child.children.create(:name => "grandchild1") grandchild2 = Category.create(:name => "grandchild2") child.children << grandchild2 grandchild3 = Category.create(:name => "grandchild2") grandchild3.parent = child parent.parent # => nil child.parent # => parent parent.children # => [child] parent.children.first.children.first # => grandchild1 parent.siblings # => [] grandchild1.siblings # => [grandchild2] parent.generation # => [parent] grandchild1.generation # => [grandchild1, grandchild2] parent.ancestors # => [] grandchild2.ancestors # => [parent, child] parent.root # => parent parent.root # => parent grandchild2.root # => parent Category.first_root # => parent Category.roots # => [parent]
Now there are some gotcha's that might not be entirely obvious to everyone, so let's clarify them here.
By default dm-is-tree allows you to save a record as a child of it self, which is quite unnatural. To prevent this, I would humbly suggest adding this custom validation code to your model(s).
class Category
<snip...>
# prevent saving Category as child of self, except when new?
validates_with_method :parent_id,
:method => :category_cannot_be_made_a_child_of_self,
:unless => :new?
protected
def category_cannot_be_made_a_child_of_self
if self.id === self.parent_id
return [
false,
"A Category [ #{self.name} ] cannot be made a child of it self [ #{self.name} ]"
]
else
return true
end
end
end
An example:
parent = Category.create(:name => "parent") child = parent.children.create(:name => 'child') child.parent = child child.save # => return false child.errors.on(:parent_id) # => ["A Category [ child ] cannot be made a child of it self [ child ]"]
By default the sorting order is alphabetic, but this spans the entire table (with all nodes), which might not be what you want.
To prevent this, order the results by :parent_id first, and secondly by :name or whatever you wish to sort by.
class Category <snip...> is :tree, :order => [:parent_id, :name] end
That's about it.
If something is not behaving intuitively, it is a bug, and should be reported. Report it here: datamapper.lighthouseapp.com/
Make it automatically prevent saving self as child of self.
Anything else missing?
Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so we don't break it in a future version unintentionally.
Commit, do not mess with rakefile, version, or history.
(if you want to have your own version, that is fine but bump version in a commit by itself we can ignore when we pull)
Send us a pull request. Bonus points for topic branches.
Copyright (c) 2011 Timothy Bennett. Released under the MIT License.
See LICENSE for details.
Credit also goes to these contributors.
Current Maintainer: Garrett Heaver (www.linkedin.com/pub/dir/garrett/heaver)
Generated with the Darkfish Rdoc Generator 2.