Links and Link Lists

A record in a database-class is defined by a »rid«. If this is stored in a class, a link is set. In OrientDB links are used to realize unidirectional 1:1 and 1:n relationships.

ActiveOrient autoloads Model-objects when they are accessed. Example: If an Object is stored in Cluster 30 and id 2, then "#30:2" fully qualifies the ActiveOrient::Model object and sets the link if stored somewhere.

  ORD.create_class 'test_link', 'test_base'

  link_document =  TestLink.create  att: 'one attribute'
  base_document =  TestBase.create  base: 'my_base', single_link: link_document

base_document.single_link just contains the rid. When accessed, the ActiveOrient::Model::Testlinkclass-object is autoloaded and

   base_document.single_link.att

reads the stored content of link_document.

To store a list of links to other Database-Objects, a simple Array is allocated

  # predefined linkmap-properties
  TestLink.create_property  :links,  type: :linklist, linkedClass: :test_links 
  base_document =  TestBase.create links: []  
  (0 .. 20).each{|y| base_document.links << TestLink.create( nr: y )}
  
  #or in schemaless-mode
  base_document = TestBase.create links: (0..20).map{|y| TestLink.create nr: y}
  base_document.update

base_document.links behaves like a ruby-array.

If you got an undirectional graph

a --> b ---> c --> d

the graph elements can be explored by joining the objects (a[6].b[5].c[9].d)

Refer to the "Time-Graph"-Example for an Implementation of an bidirectional Graph with the same Interface