I am trying to calculate the shortest weighted path between two nodes. Here's my User class:
class User
include Neo4j::ActiveNode
property :name, type: String
has_many :both, :friends, rel_class: :Friendship, model_class: :User
end
Users are nodes and the relationship between them is:
class Friendship
include Neo4j::ActiveRel
before_save :set_weight
from_class :User
to_class :User
type 'FRIENDSHIP'
property :weight
def set_weight
...
end
The property weight is the value of the haversine distance between both nodes.
I figured out how to write the query to get all the paths that conect user_a with user_b:
all_paths = a.query_as(:a).match_nodes(b: b).match('p=((a)-[*]-(b))').pluck(:p)
And I'm sure that I can chain methods to this query to get the shortest path based on the weight but I couldn't find the right Cypher syntax so I ended iterating every path and calculating the total weight for each path to get the shortest one:
def shortest_weighted_path(start_user_id, end_user_id)
a = User.find(start_user_id)
b = User.find(end_user_id)
all_paths = a.query_as(:a).match_nodes(b: b).match('p=((a)-[*]-(b))').pluck(:p)
paths_and_weights = {}
all_paths.each_with_index do |path, index|
total_weight = 0
path.relationships.each { |relationship| total_weight = total_weight + relationship.properties[:weight] }
paths_and_weights[index] = total_weight
end
paths_and_weights = paths_and_weights.sort_by {|_key, value| value}.to_h
shortest_path_index = paths_and_weights.keys.first
shortest_path = all_paths[shortest_path_index]
nodes_in_path = []
shortest_path.nodes.each { |node| nodes_in_path << node.properties[:uuid] }
nodes_in_path
end
Googling some more I found and example on how to calculate the shortest path with Cypher:
START startNode=node:node_auto_index(name={startNode}),
endNode=node:node_auto_index(name={endNode})
MATCH p=(startNode)-[:CONNECTED_TO*1..4]->(endNode)
RETURN p AS shortestPath,
reduce(weight=0, r in relationships(p) : weight+r.weight) AS totalWeight
ORDER BY totalWeight ASC
LIMIT 1
So my question is: how can I write this query for Neo4j.rb based in my User-Friendship example?