1

I'm adding a new vertex and an edge to an existing vertex in Datastax Graph, and I wanted to see how to do that with Datastax CassandraCSharpDriver.Graph.

The working Gremlin code looks like this: 

Vertex link1 = graph.addVertex(label, "link").property("id", "link-2")
Vertex item1 = g.V().has("item", "id", "item-1").next()
item1.addEdge('contains', link1)

But in the C# driver syntax, I was hoping to do something like this but when I execute it, the error is the "adjacency of 'contains' in direction 'OUT' has not been added to 'link'"

GraphTraversalSource g = DseGraph.Traversal(mySession);
var traversal = g.AddV("link").Property("id", "link-1")
                .AddE("contains")
                .V("item").Has("id", Eq("item-1"));
GraphResultSet result = mySession.ExecuteGraph(traversal);

I had created the edge and edge connections like this:

schema.edgeLabel("contains").multiple().create()  
schema.edgeLabel("contains")  
.connection("item", "link")  
.connection("link", "item")  
.add()

Any ideas if the schema edge is setup incorrectly or how to do this the best way in Datastax CassandraCSharpDriver.Graph?

Stanislav Kralin
  • 11,070
  • 4
  • 35
  • 58
Robert Corvus
  • 2,054
  • 23
  • 30
  • Can you post a complete example that I'm able to reproduce locally? I'm not able to run the gremlin queries at the moment. – João Reis Feb 28 '20 at 10:38
  • 1
    The complete schema should be something like this, right? `schema.propertyKey('id').Text().ifNotExists().create() schema.edgeLabel('contains').multiple().ifNotExists().create() schema.vertexLabel('item').properties('id').ifNotExists().create() schema.vertexLabel('link').properties('id').ifNotExists().create() schema.edgeLabel('contains').connection('item', 'link').connection('link', 'item').add()` – João Reis Feb 28 '20 at 10:40
  • @JoãoReis yes, that's about right – Robert Corvus Mar 02 '20 at 20:26

1 Answers1

2

Your Gremlin here:

g.AddV("link").Property("id", "link-1")
            .AddE("contains")
            .V("item").Has("id", Eq("item-1")

isn't properly formed. It should be:

g.AddV("link").Property("id", "link-1").As('l1').
  V("item").Has("id", Eq("item-1")).
  AddE('contains').To('l1')

With AddE() you need to specify the From() and the To() to identify the vertices that the edge is connecting. Without specifying those, AddE() will just use the incoming Vertex for both values creating a self-referencing edge. As a result in this case, you should only need to specify the To() as the From() is inferred.

Please note the examples in the Reference Documentation where you should see other methods to doing this.

stephen mallette
  • 45,298
  • 5
  • 67
  • 135
  • Thanks, I did something similar and I'll give you credit. I aliased both vertices, then used a "From" and "To" clause in the AddE. The exact syntax I used was more like: g.AddV("link").Property("id", "link-1").As('l1'). V("item").Has("id", Eq("item-1")).As('it1'). AddE('contains').From('it1').To('l1') – Robert Corvus Mar 02 '20 at 19:40