arangosh> db.ids.ensureIndex({ type: "persistent", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/16361", "isNewlyCreated" : true, "sparse" : false, "type" : "persistent", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/16364", "_key" : "16364", "_rev" : "_XG3zIje--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/16368", "_key" : "16368", "_rev" : "_XG3zIji--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/16371", "_key" : "16371", "_rev" : "_XG3zIji--B" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 16361 of type persistent over ["myId"]; conflicting key: 16364]