func: uid() always returns data, even if node does not exist

[aryzing]

Queries with func: uid(<the_id>) always return a node, even if the node does not exist. Is this the expected bahavior?

• What version of Dgraph are you using?
  1.0.2

• Have you tried reproducing the issue with latest release?
  yes

• Steps to reproduce the issue (command/config used to run Dgraph).
  Issue query:

{
  random_node(func: uid(0x123abc456def)) {
    uid
  }
}

• Expected behaviour and actual result.
  Expected The random_node query should be an empty array
  Actual There's an object representing the queried id, but that node does not exist!

{
  "data": {
    "random_node": [
      {
        "uid": "0x123abc456def"
      }
    ]
  },
  "extensions": {
    "server_latency": {
      "parsing_ns": 13761,
      "processing_ns": 24076,
      "encoding_ns": 336092
    },
    "txn": {
      "start_ts": 50096,
      "lin_read": {}
    }
  }
}

[pawanrawal]

This is expected behaviour. Dgraph doesn't store nodes separately. We store all data for a S P combination together. A better way to check if a node exists will be to query for _predicate_. Though that would be empty if you added and then deleted the data associated with a node.

{
  random_node(func: uid(0x123abc456def)) {
    _predicate_
  }
}

Curious to know how do you get the random uid if Dgraph didn't return it and what use case does checking for it serve?

[aryzing]

what use case does checking for it serve?

Honestly, I don't know. I discovered this while playing with dgraph b/c I mistyped an id from a previous query. I was confused for quite some time until I realized the mistake due to there being an object with the erroneous id in the JSON response.

On my part, I made the assumption that querying for non-existant uids would either error out or return nothing, so I just wanted to confirm whether I had made the wrong assumption.

Thanks for the clarification!