amazon web services - DynamoDB UpdateItem Doesn't Work -

this pretty straight out of documentation (http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/expressions.modifying.html), things aws, doesn't work , isn't documented @ all.

the following fails "the document path provided in update expression invalid update"

var messageid = "f244ed33-d678-4763-8f46-0f06514d5139" var sequenceid = "00000000-0000-0000-0000-000000000000"  var = datetime.utcnow; var lastactivitythreshold = now.subtract(timespan.fromseconds(10));  var response = client.updateitem(new updateitemrequest {     tablename = "thetable",     key = new dictionary<string, attributevalue> { { "sequenceid", new attributevalue { s = sequenceid } } },     expressionattributevalues = new dictionary<string, attributevalue>     {         {":messageid", new attributevalue {s = messageid}},         {":now", new attributevalue {n = now.ticks.tostring()}},         {":lastactivitythreshold", new attributevalue {n = lastactivitythreshold.ticks.tostring() }},     },     updateexpression = "remove messages[0] set lastactivity = :now",     conditionexpression = "messages[0] <> :messageid , (lastactivity <= :lastactivitythreshold or attribute_not_exists(lastactivity))",     returnvalues = returnvalue.updated_new }); 

this document i'm trying update (as seen in json view in aws management console):

{   "lastactivity": {     "n": "635753575712635873"   },   "messages": {     "ss": [                "f244ed33-d678-4763-8f46-0f06514d5139",       "f668d2a5-3a4a-4564-8384-5b5a51c9bad3"     ]   },   "sequenceid": {     "s": "00000000-0000-0000-0000-000000000000"   } } 

i've tried many variations of code above, striaght down removing expressionattributevalues , conditionexpression , using remove messages[0], doesn't work , throws same error.

it looks you're trying apply document path non json item. there's no concept of ordering in set, if want remove first item, you'll need load memory , iterate on it. in short, you'll need use list in case.