arangosh> db.ids.ensureIndex({ type: "persistent", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/17585", "isNewlyCreated" : true, "sparse" : false, "type" : "persistent", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/17588", "_key" : "17588", "_rev" : "_VvTSGKu---" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/17592", "_key" : "17592", "_rev" : "_VvTSGKu--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/17595", "_key" : "17595", "_rev" : "_VvTSGKu--A" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 17585 of type persistent over ["myId"]]