@brief Creates an edge from vertex *from* to vertex *to* in collection edgeCollectionName

`graph.edgeCollectionName.save(from, to, data, options)`

@PARAMS

@PARAM{from, string, required}
*_id* attribute of the source vertex

@PARAM{to, string, required}
*_id* attribute of the target vertex

@PARAM{data, object, required}
JSON data of the edge

@PARAM{options, object, optional}
See [collection documentation](../Edges/README.md)

@EXAMPLES

@EXAMPLE_ARANGOSH_OUTPUT{generalGraphEdgeCollectionSave1}
  var examples = require("@arangodb/graph-examples/example-graph.js");
  var graph = examples.loadGraph("social");
  graph.relation.save("male/bob", "female/alice", {type: "married", _key: "bobAndAlice"});
~ examples.dropGraph("social");
@END_EXAMPLE_ARANGOSH_OUTPUT

If the collections of *from* and *to* are not defined in an edge definition of the graph,
the edge will not be stored.

@EXAMPLE_ARANGOSH_OUTPUT{generalGraphEdgeCollectionSave2}
  var examples = require("@arangodb/graph-examples/example-graph.js");
  var graph = examples.loadGraph("social");
  | graph.relation.save(
  |  "relation/aliceAndBob",
  |   "female/alice",
     {type: "married", _key: "bobAndAlice"}); // xpError(ERROR_GRAPH_INVALID_EDGE)
~ examples.dropGraph("social");
@END_EXAMPLE_ARANGOSH_OUTPUT