在ArangoDB中找到具有最大价值的边沿之后的路径

Question

Lets say, that in my graph I've got edges that have field called value. After selecting start vertex I would like to find path by always selecting the edge that has the highest value. Unfortunatly I can't figure out how to write proper query, is it possible in ArangoDB?

Answer 1

Hi i am unsure what you would like to achieve, there are two possible scenarios that i can imagine from your description:

First: Shortest Path

The use-case here is you know the starting vertex and the target vertex, and you want to find the shortest (or cheapest) path between those two. The built in SHORTEST_PATH ( https://docs.arangodb.com/3.1/AQL/Graphs/ShortestPath.html#shortest-path-in-aql ) feature can serve it by defining the distance attribute in the options like this:

FOR v IN OUTBOUND @start TO @end @@edgeCollections OPTIONS {weightAttribute: "value", defaultWeight: 1}
  RETURN v

This will give you all vertices on the path from start to end which has the lowest some of value attributes. If you need the "highest value" you could copy the value and save it again with 1/value in a different field, to find the path with the fewest edges having in total the highest sum of values

Second: Sorting of edges

The use case is you only have the starting vertex and want to get the connected vertices, ordered by the value on the edges. There you can simply combine the traversal statement with a simple sort. ( https://docs.arangodb.com/3.1/AQL/Graphs/Traversals.html#graph-traversals-in-aql ):

FOR v, e IN OUTBOUND @start @@edgeCollection
  SORT e.value DESC
  LIMIT 1 /* Only pick the highest one */
  REUTRN {v: v, e: e}

Third use-case: Iterating several depth only using the highest value

The AQL in Use-case 2 can be chained up to an arbitrary depth which has to be known a-priori. So say you would like to iterate 3 steps only using the edge with highest value:

FOR v1, e1 IN OUTBOUND @start @@edgeCollection
  SORT e1.value DESC
  LIMIT 1 /* Only pick the highest one */
  /* Depth 1 done. now depth 2*/
  FOR v2, e2 IN OUTBOUND v1 @@edgeCollection
    SORT e2.value DESC
    LIMIT 1 /* Only pick the highest one */
    FOR v3, e3 IN OUTBOUND v2 @@edgeCollection
      SORT e3.value DESC
      LIMIT 1 /* Only pick the highest one */
      RETURN [v1,v2,v3]

Forth use-case:

The depth is not known a-priori, in this case pure AQL in the currently release version (3.1) cannot formulate this. It will be easier to use a Foxx service ( https://docs.arangodb.com/3.1/Manual/Foxx/#foxx ) using the traversal module ( https://docs.arangodb.com/3.1/Manual/Graphs/Traversals/UsingTraversalObjects.html#getting-started ) in JavaScript which is a bit more flexible, but can only be implemented in Javascript.