docs/src/recipes/edge-move.asciidoc

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[[edge-move]]
== Moving an Edge

image:gremlin-edge.png[width=145]

Aside from their properties, edges are immutable structures where the label and the related in and out vertices
cannot be modified. To "move" an edge from one vertex to another, it requires that the edge be dropped and a new edge
be created with the same properties and label. It is possible to simulate this "move" in a single traversal as
follows:

[gremlin-groovy,modern]
----
g.V().has('name','marko').
  outE().inV().
  path().by('name').by(elementMap())
----

The "marko" vertex contains a "knows" edge to the "vadas" vertex. The following code shows how to "move" that edge to
the "peter" vertex in a single traversal:

[gremlin-groovy,modern]
----
g.V().has('name','marko').as('a').
  outE('knows').as('e1').filter(inV().has('name','vadas')).       <1>
  V().has('name','peter').
  addE('knows').from('a').as('e2').                               <2>
  sideEffect(select('e1').properties().
             unfold().as('p').
             select('e2').
             property(select('p').key(), select('p').value())).   <3>
  select('e1').drop()                                             <4>
g.V().has('name','marko').
  outE().inV().
  path().by('name').by(elementMap())
----

<1> Find the edge to "move" and label that as "e1". It will be necessary to reference this later to get the edge
properties to transfer to the new "moved" edge.
<2> Add the "moved" edge and label it as "e2".
<3> Use a `sideEffect()` to transfer the properties from "e1" to "e2".
<4> Use `drop()` to get rid of the old edge at "e1" now that the new "e2" edge is in place.