arangosh> db.ids.ensureIndex({ type: "persistent", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/17574", "isNewlyCreated" : true, "sparse" : false, "type" : "persistent", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/17577", "_key" : "17577", "_rev" : "_Vsb0bYK---" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/17581", "_key" : "17581", "_rev" : "_Vsb0bYO---" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/17584", "_key" : "17584", "_rev" : "_Vsb0bYS---" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 17574 of type persistent over ["myId"]]