Creating Edge if doesn't exist

[Michael Kolback]

Trying to replicate the following query in GremlinQ, but having some issues.

g.V().has('person','name','vadas').as('v').
           V().has('software','name','ripple').
           coalesce(__.inE('created').where(outV().as('v')),
                    addE('created').from('v').property('weight',0.5))

What I have currently is

await _g
                .V<T>()
                .Where(sourceVertexExpression)
                .As((__, sourceVertex) => __
                    .V(vertexToLink.Id)
                    .Coalesce(
                        (q) => q.InE<Contains>().Where(),
                        (q) => q.AddE<Contains>().From(sourceVertex)
                    )
                )
                .FirstOrDefaultAsync();

Not sure what to use in the Where to match the out vertex to the step label. Any help would be greatly appreciated.

[Daniel Weber]

.where(outV().as('v')) is effectively an identity() step since you're applying it on an edge, which must have an outV() so the where in this case won't ever filter out anything. So I assume the raw Gremlin is already not doing what you're trying to do.

You're probably aiming for .where(outV().where(eq('v')) which is just .Where(__ => __.OutV().Where(x => x == sourceVertex.Value)) in Gremlinq.

[Michael Kolback]

Thanks @danielcweber!

So i reworked the query to this

await _g
                .V<T>()
                .Where(sourceVertexEqualityExpression)
                .As((__, sourceVertex) => __
                    .V(vertexToLink.Id)
                    .Coalesce(
                        (q) => q.InE<Contains>().Where(__ => __.OutV().Where(x => x == sourceVertex)),
                        (q) => q.AddE<Contains>().From(sourceVertex)
                    )
                )
                .FirstOrDefaultAsync();

Now im getting an issue where the coalesce is breaking during compile time with the following exception

The type arguments for method 'IGremlinQueryBaseRec<IVertexGremlinQuery<object>>.Coalesce<TTargetQuery>(params Func<IVertexGremlinQuery<object>, TTargetQuery>[])' cannot be inferred from the usage. Try specifying the type arguments explicitly.

Not quite sure what the type arguments should be in this situation.

[Daniel Weber]

You need a common type for both the queries that Coalesce takes. One of them is currently probably something like IInEdge.... and the other one just IEdge.... or something. Try the various "Force...." -methods to force them to the lowest common interface ("ForceEdge" will probably do).

[Michael Kolback]

Got it working, thanks!