Gremlin.Net查询JanusGraph边时出现RelationIdentifier反序列化异常求助

Hey there! Let's work through this deserialization issue you're hitting with Gremlin.Net and JanusGraph. The error about missing a deserializer for janusgraph:RelationIdentifier happens because your .NET client doesn't know how to handle JanusGraph's custom edge ID type—even though your server is configured correctly, the client needs matching setup to recognize these JanusGraph-specific types.

Here's how to fix this step by step:

1. Match Serializers Between Client and Server #

First, make sure your Gremlin.Net client uses the same serializer type as your JanusGraph server. From your server config, GraphSONMessageSerializerGremlinV2d0 with the JanusGraph IoRegistry is a solid choice, since it's easier to customize for JanusGraph's types in .NET.

2. Create a Custom Deserializer for RelationIdentifier #

JanusGraph uses RelationIdentifier as the edge ID type, which isn't built into Gremlin.Net. You'll need to define a class to represent this type and a serializer to handle converting it between GraphSON and .NET objects:

// First, define the RelationIdentifier class to mirror JanusGraph's type
public class RelationIdentifier
{
    public string Value { get; set; }

    public static RelationIdentifier FromString(string value)
    {
        return new RelationIdentifier { Value = value };
    }
}

// Then create a custom GraphSON serializer for this type
public class RelationIdentifierGraphSONSerializer : IGraphSONSerializer
{
    public dynamic ObjectToGraphSON(object obj)
    {
        var rid = (RelationIdentifier)obj;
        return new Dictionary<string, dynamic>
        {
            { "@type", "janusgraph:RelationIdentifier" },
            { "@value", rid.Value }
        };
    }

    public object GraphSONToObject(dynamic graphsonObject)
    {
        return RelationIdentifier.FromString(graphsonObject["@value"].ToString());
    }
}

3. Configure Your Cluster to Use the Custom Serializer #

When setting up your Gremlin.Net Cluster instance, pass in the customized GraphSON serializer so it can handle RelationIdentifier:

// Build the custom serializer
var graphSonSettings = new GraphSONSerializerSettings
{
    CustomSerializers = new Dictionary<string, IGraphSONSerializer>
    {
        { "janusgraph:RelationIdentifier", new RelationIdentifierGraphSONSerializer() }
    }
};
var serializer = new GraphSONMessageSerializerGremlinV2d0(graphSonSettings);

// Initialize the cluster with the custom serializer
var cluster = Cluster.Builder()
    .AddContactPoint("your-janusgraph-host") // Replace with your actual host
    .Port(8182) // Default Gremlin server port
    .Serializer(serializer)
    .Build();

4. Alternative: Adjust Your Gremlin Query (Quick Fix) #

If you don't need the full edge object right now, you can modify your query to return only the properties you need instead of the entire edge. This avoids triggering the deserialization issue entirely:

g.V(61464).outE('father').project('label', 'inVertexId', 'properties')
    .by(label())
    .by(inV().id())
    .by(valueMap())
    .toList()

This query returns a structured map with edge details without sending the RelationIdentifier type over the wire.

内容的提问来源于stack exchange，提问作者janus graph