Select a vertex if the edge to the vertex has a property value, otherwise choose another vertex with a different edge property value

Question

I am trying to grab vertices connecting a Request vertex to each Card vertex. The card-to-request relationship is one-to-many (each card has many requests).

A card may be connected to a request with the property "Status": "In Use" if the card is being used. Each card will also be connected to many requests with the properties "Status": "Future Use" or "Past Use".

I am trying to create a table that displays the most recent use of each card.

Thus, I want to return a request if the edge connecting it to the card has the property "Status": "In Use".

If the card is not currently in use, I look for the request that most recently used the card ("Status": "Past Use").

If the card has never been used, I look for the soonest upcoming request that will use the card ("Status": "Future Use").

I have attempted to use coalesce:

.coalesce(
 select('request')
  .outE().hasLabel('AssignedTo}').has('Status', 'In Use'),
 select('request')
  .outE().hasLabel('AssignedTo').has('Status', 'Past Use').order().by('Timestamp', decr).limit(1),
 select('request')
  .outE().hasLabel('AssignedTo').has('Status', 'Future Use').order().by('Timestamp', incr).limit(1)
).as('status')

But this only returns a single record (In Use). Another version:

.coalesce(
 select('card')
  .inE().hasLabel('AssignedTo}').has('Status', 'In Use'),
 select('card')
  .inE().hasLabel('AssignedTo').has('Status', 'Past Use').order().by('Timestamp', decr).limit(1),
 select('card')
  .inE().hasLabel('AssignedTo').has('Status', 'Future Use').order().by('Timestamp', incr).limit(1)
).as('status')

This only returned two records (both In Use).

I tried choose awhile ago and couldn't get that to work either (don't recall what happened exactly).

Expected:

Get back a single vertex that has an edge with the property "Status": "In Use".

If this edge doesn't exist, get the most recent vertex that has an edge with the property "Status": "Past Use".

If there are no edges that qualify, get the soonest upcoming vertex that has an edge with the property "Status": "Future Use".

score 1 · Accepted Answer · answered Nov 07 '19 at 20:13

I'm not sure what went wrong with your query since you didn't post it entirely, but this should work:

g.V().hasLabel("Card").as("c").coalesce(
    outE("assigned").has("status", "In Use"),
    outE("assigned").has("status", "Past Use").order().by("Timestamp", desc).limit(1),
    outE("assigned").has("status", "Future Use").order().by("Timestamp", asc).limit(1),
).as("s").inV().as("r")
.select("c","s","r").by("name").by("status").by("name")

Select a vertex if the edge to the vertex has a property value, otherwise choose another vertex with a different edge property value

1 Answers1