node.js - condition expression on put item in dynamodb -

in dynamodb using putitem want run test if item1 , item2 matches existing record, want nothing, if dont, want putitem.

my table

field1    field2    field3  item1     item2     item3  item1b    item2b    item3b  var item = {field1: myfield1, field2: myfield2, field3: myfield3}  

so if

conditionexpression: myfield1 != item1 , myfield2 != item2  

i want

dynamo.putitem....... 

i had thought done without query

i tried using

conditionexpression: "attribute_not_exists(field1) , attribute_not_exists(field2)" 

but didn't see results want