lib/neo4j/graph/sequential_id.nit

   1 # This file is part of NIT ( http://www.nitlanguage.org ).
   2 #
   3 # This file is free software, which comes along with NIT. This software is
   4 # distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
   5 # without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
   6 # PARTICULAR PURPOSE. You can modify it is you want, provided this header
   7 # is kept unaltered, and a notification of the changes is added.
   8 # You are allowed to redistribute it and sell it, alone or is a part of
   9 # another product.
  10
  11 # Provides a sequential identification scheme for Neo4j nodes.
  12 module neo4j::graph::sequential_id
  13
  14 import graph
  15 private import pipeline
  16
  17
  18 # A Neo4j node collection using a sequential identification scheme.
  19 #
  20 # The local IDs are sequential numbers (integers) starting at `1`.
  21 #
  22 # Note: When loading nodes, the local IDs should forms a mostly contiguous
  23 # range starting at `1`. Else, this collection will consume a lot of memory.
  24 # Futhermore, the local IDs **must** be positive.
  25 #
  26 # ~~~nit
  27 # var nodes = new SequentialNodeCollection("id")
  28 # var a = nodes.create_node
  29 # var b = new NeoNode
  30 # var c = new NeoNode
  31 #
  32 # nodes.register b
  33 # c["id"] = 4
  34 # nodes.add c
  35 # assert a["id"] == 1
  36 # assert b["id"] == 2
  37 # assert c["id"] == 4
  38 # assert nodes.to_a == [a, b, c]
  39 # ~~~
  40 class SequentialNodeCollection
  41         super NeoNodeCollection
  42
  43         redef type ID_TYPE: Int
  44
  45         private var nodes = new Array[nullable NeoNode]
  46
  47         redef fun iterator do return new NullSkipper[NeoNode](self.nodes.iterator)
  48
  49         redef fun get_or_null(id) do
  50                 if id < 0 or id > nodes.length then return null
  51                 return nodes[id]
  52         end
  53
  54         redef fun register(node) do
  55                 nodes.add node
  56                 id_of(node) = nodes.length
  57         end
  58
  59         redef fun add(node) do
  60                 var id = node[id_property]
  61                 assert id isa Int else
  62                         sys.stderr.write "The local ID must be an `Int`.\n"
  63                 end
  64                 assert id >= 0 else
  65                         sys.stderr.write "The local ID must be greater or equal to 0. Got {id}.\n"
  66                 end
  67                 # Pad with nulls.
  68                 var delta = id - nodes.length
  69                 while delta > 0 do
  70                         nodes.add null
  71                         delta -= 1
  72                 end
  73                 nodes[id] = node
  74         end
  75
  76         redef fun remove_at(id) do
  77                 nodes[id] = null
  78         end
  79 end