dgr_graph, query an edge
in the graph (defined by a pair of node IDs extant in the graph) and perform
operations on the relationship for that edge.
edge_rel(graph, from, to, action = "read", value = NULL)dgr_graph that is created using
create_graph.delete,
remove, or drop. To add a relationship to an edge with no
set relationship, use add or create. To update an edge
relationship, use update. To return the value of an edge
relationship, use read. To determine whether there is a set
relationship, use check.dgr_graph.