arangosh> db.ids.ensureUniqueSkiplist("name.first", "name.last");
{ 
  "id" : "ids/1182921611", 
  "type" : "skiplist", 
  "fields" : [ 
    "name.first", 
    "name.last" 
  ], 
  "unique" : true, 
  "sparse" : false, 
  "isNewlyCreated" : true, 
  "code" : 201 
}
arangosh> db.ids.save({ "name" : { "first" : "hans", "last": "hansen" }});
{ 
  "_id" : "ids/1183249291", 
  "_rev" : "1183249291", 
  "_key" : "1183249291" 
}
arangosh> db.ids.save({ "name" : { "first" : "jens", "last": "jensen" }});
{ 
  "_id" : "ids/1183445899", 
  "_rev" : "1183445899", 
  "_key" : "1183445899" 
}
arangosh> db.ids.save({ "name" : { "first" : "hans", "last": "jensen" }});
{ 
  "_id" : "ids/1183642507", 
  "_rev" : "1183642507", 
  "_key" : "1183642507" 
}
[ArangoError 1210: cannot create document, unique constraint violated]