recursive query not expanding

[pjebs]

This is the same query/schema/data as #3582

I believe it is an independent issue but not sure: @martinmr

For the query:

q = `
		query withvar($hashid: string) {
			chain(func: eq(node.hashid, $hashid)) @recurse(loop:false) {
				uid
				node.owner
				user.name
				node.hashid
				node.xdata
				node.parent @facets @facets(eq(facet, "required") or eq(facet, "recommended"))
			}
		}
	`

When a node reappears deeper in, it is not expanding the node.owner. It correctly expands in earlier on.

[pjebs]

See <------------------------ below

{
  "chain": [
    {
      "uid": "0x4e27",
      "node.owner": [
        {
          "uid": "0x4e21",
          "user.name": "johny"
        }
      ],
      "node.hashid": "jjtn4cdirv",
      "node.xdata": "{\"title\":\"The Two Towers\",\"authors\":[\"J. R. R. Tolkien\"]}",
      "node.parent": [
        {
          "uid": "0x2711", <----------------------------
          "node.owner": [ <--------------- EXPANDED
            {
              "uid": "0x1",
              "user.name": "powerofgod"
            }
          ],
          "node.hashid": "myin9aksq",    
          "node.xdata": "{\"title\":\"The Da Vinci Code\",\"authors\":[\"Dan Brown\"]}",
          "node.parent|facet": "required"
        },
        {
          "uid": "0x4e25",
          "node.owner": [
            {
              "uid": "0x1",
              "user.name": "powerofgod"
            }
          ],
          "node.hashid": "r9t9rc4ip",
          "node.xdata": "{\"title\":\"Pride and Prejudice\",\"authors\":[\"Jane Austen\"]}",
          "node.parent": [
            {
              "uid": "0x2711", <------------------------SAME NODE (no expanded node.owner)
              "node.hashid": "myin9aksq",
              "node.xdata": "{\"title\":\"The Da Vinci Code\",\"authors\":[\"Dan Brown\"]}",
              "node.parent|facet": "required"
            }
          ],
          "node.parent|facet": "recommended"
        },
        {
          "uid": "0x4e26",
          "node.owner": [
            {
              "uid": "0x4e21",
              "user.name": "johny"
            }
          ],
          "node.hashid": "35t8qc8i5",
          "node.xdata": "{\"title\":\"The Hobbit\",\"authors\":[\"J. R. R. Tolkien\"]}",
          "node.parent": [
            {
              "uid": "0x2711", <------------------------SAME NODE (no expanded node.owner)
              "node.hashid": "myin9aksq",
              "node.xdata": "{\"title\":\"The Da Vinci Code\",\"authors\":[\"Dan Brown\"]}",
              "node.parent|facet": "recommended"
            },
            {
              "uid": "0x4e25",
              "node.hashid": "r9t9rc4ip",
              "node.xdata": "{\"title\":\"Pride and Prejudice\",\"authors\":[\"Jane Austen\"]}",
              "node.parent|facet": [ <--------------- ISSUE #3582 (different issue)
                "required",
                "required"
              ]
            }
          ],
          "node.parent|facet": "recommended"
        }
      ]
    }
  ]
}

[pjebs]

/cc @power-f-GOD

[martinmr]

This is most likely because you reached the maximum depth allowed. Try playing with the depth parameter. I would start with 5 and see if that makes those nodes appear.

link to the docs: https://docs.dgraph.io/query-language/#recurse-query

I'll also document what the default depth is since it's currently unclear from the docs.

[pjebs]

My use case requires no limits

[pjebs]

If I was making a dependency tool like npm I can't have a limit

[martinmr]

Nevermind, I checked the code. The default depth when loop is set to false is math.MaxUint64 so that's not the problem. The problem is you have set loop to false. Once a node has been seen, it won't be expanded again. If that's not the behavior you want, then you have to set loop to true and pass a depth parameter that is greater than zero.

If your use case requires no limits, then you must set loop to false, which will run the query until it reaches all the nodes but won't follow loops. Otherwise your queries will never return.

[pjebs]

Seems like a bug to me. The query implies the node should always be expanded, even if it means dgraph keeps the previously encountered node in memory and reuses it.

[martinmr]

This is not a bug. You specifically set loop to false.

[pjebs]

You are looking at it from an implementation point of view. That is not what the query implies irrespective of loop setting. @manishrjain

[martinmr]

That is exactly what the query implies. If you want to follow loops you need to set loop to true and provide a depth parameter. Otherwise Dgraph would keep on expanding the graph endlessly.

[pjebs]

My concern is regarding why the loop setting is effecting the JSon payload being returned. I understand loop should stop expanding endlessly. But the query's "footprint" says for each node (uid) found, the JSon response should contain an expanded 'node.owner'. the response should supply it, even if it means storing encountered nodes in memory and showing it.

[pjebs]

The footprint of each returned object is:

uid
				node.owner
				user.name
				node.hashid
				node.xdata
				node.parent @facets @facets(eq

All returned objects should look like that as much as possible.

[martinmr]

This is not different than a predicate not showing up when it doesn't exist. In the first appearance of the node, node.owner was expanded because it had not been traverse that. After that, that edge won't be expanded because loop is set to false. Dgraph doesn't show anything. It could set node.owner to an empty object or list but that would not be very useful. You are right in that Dgraph will try to adhere to the query format requested but it won't force it in situations where it does not make that much sense.

[pjebs]

I'm suggesting it should be in the case in this scenario without having to "force it". Since the uid has been encountered before, DGraph has all the data required to properly create an object in the eventual json which will look like the footprint suggested in the query.

It is essentially doing this: https://github.com/thehonestscoop/lemma-chain/blob/master/find_chain.go#L242 (but the DGraph side rather than client).

It is not hard to do from a technical point of view, it doesn't violate loop limit and returns what the query intuitively expects.