Currently, it appears that the _ref field of an edge can be patched/updated by dispatching a patch/update request against the relationship endpoint. This amounts to detaching and re-attaching one end of an edge. So either:
- this possibility must be excluded, or
- if this possibility is supported, the following actions must be taken:
- notify the origin vertex that its edge has been updated,
- notify the vertex from which the edge was detached that an edge has been deleted
- notify the newly-connected-to vertex that it has gained an edge.
If we decide to support this functionality, integration tests must be written. In either case, the feature/limitation must be documented.