Module: Dagnabit::Node::ClassMethods

Defined in:
lib/dagnabit/node/class_methods.rb

Instance Method Summary collapse

Instance Method Details

#subgraph_from(*roots) ⇒ Object

Returns a subgraph rooted at a given set of nodes.

While you can retrieve all descendants of a node pretty easily (i.e. node.descendants), and all links from a node really easily (i.e. +node.links_as_ancestor), it’s not quite as straightforward to get the nodes and edges (direct edges, that is) out of a graph.

The subgraph is returned as an object with two properties: nodes and edges. Both properties are instances of the Set class.

Examples

In the following examples, the node class is called Node. Variables of the form nM, where M is an integer, denote Node instances.

Retrieve all descendants of n1 and all direct edges “underneath” n1 (i.e. n1 to its children and direct edges for each of n1’s descendants):

<pre> Node.subgraph_from(n1)

> #<Graph nodes=… edges=…>

</pre>

Same as above, but builds a graph using n1 and n2 as roots.

<pre> Node.subgraph_from(n1, n2) </pre>

Usage tip

subgraph_from forces loading of the descendants and links_as_parent links_as_parent associations on Node. In some situations, you may experience better performance if you use ActiveRecord’s eager-loading capabilities when using subgraph_from:

<pre> roots = Node.find(…, :include => [:descendants, :links_as_parent]) Node.subgraph_from(roots) </pre>



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# File 'lib/dagnabit/node/class_methods.rb', line 50

def subgraph_from(*roots)
  OpenStruct.new.tap do |g|
    g.nodes = all_nodes_of(roots)
    g.edges = direct_edges_of(roots)
  end
end