arangosh> db.ids.ensureIndex({ type: "persistent", fields: [ "myId" ], unique: true }); { "id" : "ids/15261", "type" : "persistent", "fields" : [ "myId" ], "unique" : true, "sparse" : false, "isNewlyCreated" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/15264", "_key" : "15264", "_rev" : "_UWy-OGG---" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/15268", "_key" : "15268", "_rev" : "_UWy-OGK---" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/15271", "_key" : "15271", "_rev" : "_UWy-OGO---" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: cannot create document, unique constraint violated]