从 Go 在 Gremlin 中插入多个顶点

Question

I've written the following Go code to upsert and array of vertices in Go. First off, the code has not effect. It doesn't error out, it just doesn't do the upserts.

Second, is this the most efficient way to upsert a batch of vertices using Gremlin?

func (n NeptuneGremlinGraph) Put(assetID string, version string, records []les.DeltaEditRecord) error {
    g := gremlin.Traversal_().WithRemote(n.connection)
    for _, r := range records {
        promise := g.V().HasLabel("Entity").Property("asset_id", assetID).Property("version", version).Property("entity_id", r.EntityID).Fold().
            Coalesce(g.V().Unfold(),
                g.AddV("Entity").Property("asset_id", assetID).Property("version", version).Property("entity_id", r.EntityID)).Iterate()
        err := <-promise
        if err != nil {
            return err
        }
    }
    return nil
}

This is using the tinkerpop Go driver gremlingo.

Answer 1

Your Coalesce looks wrong. Can you please try

Coalesce(AnonT.Unfold(),
         AnonT.AddV("Entity").Property("asset_id", assetID).Property("version", version).Property("entity_id", r.EntityID)).Iterate()

This assumes AnonT was defined as

var AnonT = gremlingo.T__

In your original query, the Coalesce started with gV().Unfold() which is going to always yield results (unless the graph is empty) so the alternate part of the Coalesce will never get executed.

Using the Fold ... Coalesce pattern is a perfectly reasonable way to do a "create if not exist" type of operation. Note that in Apache TinkerPop 3.6.xa new step called MergeV (along with a corresponding MergeE ) was added. This will help simplify these types of tasks.

It looks from your code sample that you may be using Amazon Neptune. If so, support for MergeV is not quite there yet in Neptune, so keep using the Coalesce idiom until Neptune adds that support.

UPDATED based on comment discussion

Also, as discussed in the comments, this line

g.V().HasLabel("Entity").Property("asset_id", assetID).Property("version", version).Property("entity_id", r.EntityID).Fold().

should use Has instead of Property