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ArangoDB: order in graph traversal

I have a pretty standard graphql which represent a tree structure:

graph

I would like to make a graph traversal and force the order according to the order I set on each edge:

A -> C

A -> B -> E

A -> B -> D

I tried to add a SORT on my query, but it sorts the whole resulting array which is not what I want:

FOR v, e, p IN 1..1000 OUTBOUND A
    edge_collec
    SORT e.order
    RETURN v

Is there a way to do this using AQL?

Solution

  • What the query does is:

    • Follow all outgoing edges in edge collection edge_collec from start vertex A
    • Then sort in ascending order by edge attribute order
    • Return the vertices (the last vertex of each found path)

    The edge attribute e.order is either 0 or 1:

    • A --[ order: 1 ]--> B
    • A --[ order: 0 ]--> C
    • B --[ order: 1 ]--> D
    • B --[ order: 0 ]--> E

    Sorting by order will return C and E (0) before B and D (1). Because two edges have the same value, it's undefined whether C or E is returned first, and whether B or D is returned third.

    If you want the vertices at depth = 1 to be returned before the vertices at depth = 2, but still sort by order on each depth level, you can use:

    SORT LENGTH(p.edges), e.order

    LENGTH(p.edges) gives you the current depth of the traversal. It first sorts by depth, then by the edge attribute and will give you the desired result order: C B E D