Filter neighbour's INBOUND vertices with path labels in ArangoDB - arangodb

Question

I have the following graph:
I'd like to write an AQL query that returns all vertices which are neighbor's INBOUND vertices colored in RED from the start vertex colored in GREEN.
I tried the following AQL to retrieve red vertices from the green vertex.
WITH collection_A, collection_W
LET A_Neighbors = (FOR t IN collection_edges
FILTER t._to == 'collection_W/W'
RETURN t._from)
let all_w = []
for item in A_Neighbors
let sub_w = (for v1 in collection_edges
FILTER v1._to == item
return v1 )
return APPEND(all_w, sub_w)
Is there any good solution other than this? Because I'm not sure this gives the correct values for start vertex collection_W/W.
My collection_edges contains following two kind of documents.
{
_from: collection_W/w,
_to: collection_A/a,
label: INBOUND
}
and
{
_from: collection_A/a,
_to: collection_W/w,
label: OUTBOUND
}

Answer 1

Given the diagram, I would suggest using a graph traversal specific [min[..max]] value, like this (using an anonymous graph):
WITH collection_A, collection_W
FOR vertex IN 2 ANY 'collection_W/W' // green start node
collection_edges
RETURN vertex
The [min[..max]] value can be a range (1..3) or it can be a single value (1).
0 will return the start node
1 will return adjacent nodes
2 will skip the adjacent nodes and return only nodes at the next level (if any)
2..999 will return all nodes (up to 999 hops away) from the start node
Further, if you want to make sure that you're only returning nodes from a specific collection, add a filter for that:
WITH collection_A, collection_W
FOR vertex IN 2 ANY 'collection_W/W' // green start node
collection_edges
FILTER IS_SAME_COLLECTION('collection_W', vertex)
RETURN vertex
You can also filter on edges (if you've added a specific attribute/value to your edges):
WITH collection_A, collection_W
FOR vertex, edge IN 2 ANY 'collection_W/W' // green start node
collection_edges
FILTER edge.someProperty == 'someValue' // only return vertices that are beyond matching edges
RETURN vertex
Or limit the traversal with PRUNE:
WITH collection_A, collection_W
FOR vertex, edge IN 2 ANY 'collection_W/W' // green start node
collection_edges
PRUNE edge.someProperty == 'someValue' // stop traversal when this is matched
RETURN vertex