Dgraph: Store list of predicates per entity

[manishrjain]

We should be able to store a list of all predicates corresponding to an entity. We can do so by having an internal predicate, say _edge_; where we can SET <entity> <_edge_> "pred"@ts .. This would allow us to query all the predicates corresponding to one entity; which would then allow various sort of queries required by users.

[F21]

It you are able to store all the predicates for a given entity, would it make sense to implement the deletion of all predicates for a given entity to simulate deleting a node?

[manishrjain]

Yes, we could do it then.

[janardhan1993]

Pasting the discussion we had on slack.

mrjn [11:19 AM]
Conclusion: We can store (internal-pred, node) -> (list of predicate values). This would require storing a list of values; which is what @tzdybal has sort of already done; we just need to extend that.

janardhan [11:22 AM]
Yep, for each mutation we would need to send list of (sub, pred) pairs to the server serving internal-pred predicate.
If a user wants to expand on a node, we would query (internal-pred, node) pl right ?

mrjn [11:22 AM]
yeah.

[11:22]
And we'd need to modify the query lang, so we can do that lookup for preds, and expansion on those preds in the same query.

[ashwin95r]

This can be done now 509c28d2f6b36bb345cea0499dd8dfd77111df33
_predicate_ returns the list of predicates.
expand(_all_) helps in expanding on all the predicates.

[F21]

@ashwin95r Does 509c28d allow the deletion of nodes without the subject and predicate?

For example:

mutation {
  delete {
     <0xf11168064b01135b> .
  }
}

[ashwin95r]

Not yet @F21. I'll create a new issue for that. Though we support S P * deletion if that helps.