Reverse Edges when using both DQL and GraphQL

Users Dgraph
1

I have a single instance of Dgraph that I use for both DQL and GraphQL queries, and I define both schema types. In general this works well, but i have an issue making reverse edges work nicely across both.

In DQL it is simple, i can link TypeA to TypeB with a TypeA.owns edge, with an @reverse directive. This results in a single predicate on TypeA, and i can navigate from TypeB to TypeA with ~TypeA.owns query.

For the GraphQL schema, I can reuse the outbound edge predicate with owns: [TypeB] on TypeA, as it reuses the existing TypeA.owns predicate from DQL schema. However, for the reverse edge it seems I have to add an extra predicate to my schema. ~owns: [TypeB] @dgraph(pred: "~TypeA.owns") is invalid syntax as ~ is not allowed.

My current solution is to have owns: [TypeB] @hasInverse(field: ownedBy) on TypeA and ownedBy: [TypeA] on TypeB. I’d prefer to avoid this as it is simpler to use the owns and ~owns construct in DQL, and leave dgraph to manage the creation of reverse edges etc. Is there some way to acheive this without the extra predicate?

Thanks,
Rob

2

Why not just use the DQL reverse method and use Custom query on GraphQL instead?

3

Thanks, I looked at the docs for Custom Queries but I cant see how I could use this to redirect one GraphQL predicate to a ~Type.predicate from DQL, do you have an example of how to do this? I think an entire DQL query block to retreive a single predicate per node wouldnt be performant enough in this case.

4

This example isn’t precise or tested. I did based on my own intuition.

type Query {
  queryUserSomething: [SomethingCount] @custom(dql: """
	query {
		queryUserTweetCounts(func: type(Something)) {
			~Type.predicate
		}
	}
	""")
}

Not sure what you mean. You mentioned GraphQL, so I thought you were using GraphQL. In that case, the example above would fit.

Well, there isn’t another way. I haven’t done it. And as both inverse and reverse are completely different approaches, I think it will be hard to sync them.

5

For future people seeing this thread, what I was attempting to do is possible, see the answers in these threads: hasInverse and how its different from using @reverse on predicates - #3 by RJKeevil Real inverse relation on GraphQL schema - #12 by pawan