arangosh> db.test.ensureIndex({ type: "hash", fields: [ "a[*]" ] }); { "id" : "test/15142", "type" : "hash", "fields" : [ "a[*]" ], "selectivityEstimate" : 1, "unique" : false, "sparse" : false, "isNewlyCreated" : true, "code" : 201 } arangosh> db.test.save({ a : [ 1, 2 ] }); { "_id" : "test/15153", "_key" : "15153", "_rev" : "_UWy-M42---" } arangosh> db.test.save({ a : [ 1, 3 ] }); { "_id" : "test/15157", "_key" : "15157", "_rev" : "_UWy-M46---" } arangosh> db.test.save({ a : null }); { "_id" : "test/15160", "_key" : "15160", "_rev" : "_UWy-M5----" }