Relay: Duplicate nodes not allowed in a connection

[sdcooke]

We have a connection that can return a node twice (a user's listening history - i.e. you can listen to the same show twice). I realise that the name "connection" implies that each edge is to a unique node, but does that have to be the case? The cursor pagination is useful for all types of lists.

The warnings we get in this case are:

Attempted to add an ID already in GraphQLSegment
Attempted to add noncontiguous index to GraphQLSegment: 11 to (0, 9)

This is because the edge ID is generated by:

var edgeID = require('./generateClientEdgeID')(connectionID, nodeID);

A potential solution might be to get the cursor into the edgeID?

Happy to be told that you don't think connections should be used for this - there are other solutions such as duplicating the pagination functionality or changing the data model (in this case we could have connection -> edge -> listen -> show) but if there's no reason why connection nodes have to be unique fixing that would be the easiest solution!

[yuzhi]

Currently, we expect the nodes to be unique. This is because GraphQLSegment is also trying to support the find call and uses the node id in a couple other places. However, that might change in the future. For right now, I think what you suggested with changing the data model is perfect connection -> edge -> listen -> show.

[sibelius]

@yuzhi can we improve the warning message to point out the exactly nodes that have duplicated keys?