Azure CosmosDB Gremlin查询：获取含边及无边的User顶点关联信息

I get exactly what you're needing—you want a single query that pulls every User vertex, whether it has connections or not, and includes all the edge metadata (direction, edge properties) along with the related vertices so you can map everything correctly in your C# app. Let's fix this with a query that uses coalesce to handle both scenarios (users with edges and users without) while preserving all the edge context you need.

Working Gremlin Query for Azure Cosmos DB Graph API #

g.V().hasLabel('User')
  .project('User', 'Edges')
    .by(valueMap(true)) // Returns all User properties (including id/label)
    .by(
      coalesce(
        bothE().project('Edge', 'Direction', 'RelatedObject')
          .by(valueMap(true)) // Get all edge properties
          .by(choose(
              __.is(outE), constant('out'),
              constant('in')
            )) // Identify if edge is outgoing or incoming
          .by(otherV().valueMap(true)), // Get the connected vertex's properties
        constant([]) // Return empty array if no edges exist
      )
    )

Breakdown of How This Works: #

• project('User', 'Edges'): Structures the result into two clear sections—one for the User vertex itself, and one for its associated edges (if any).
• by(valueMap(true)): For the User section, this grabs all vertex properties (including system properties like id and label). If you only need the user's ID, replace this with by(id) to keep results lean.
• coalesce(...): This is the key to handling edge-less users. It first tries to fetch all edges and their details; if there are no edges, it falls back to returning an empty array instead of dropping the user entirely.
• Edge Details: For each edge, we use project to capture:
  • The edge's own properties (via valueMap(true)).
  • The edge direction (out or in) using choose to check if it's an outgoing edge (outE) or incoming edge.
  • The full properties of the connected vertex (RelatedObject).

Why This Fixes Your Original Issues: #

• Unlike your first query (path()), this includes all User vertices—even those with no edges (they'll have an empty Edges array).
• Unlike your second attempt with fold(), this preserves the critical edge metadata (direction and edge properties) so you can correctly map how each User relates to other objects in your C# code.

Customization Tips: #

• If you don't need all properties, adjust valueMap(true) to specific properties (e.g., valueMap('name', 'email')) to reduce payload size.
• If you only care about edge direction and the related vertex ID, simplify the edge project to:

  bothE().project('Direction', 'RelatedObjectId')
    .by(choose(__.is(outE), constant('out'), constant('in')))
    .by(otherV().id())
  

内容的提问来源于stack exchange，提问作者Dejan Janjušević