title: DynamoDBMapper for conditional saves
body: <p>I'm using DynamoDBMapper and would like to conditionally save if and only if the hashkey and range key combination does not exist. I know there are ways to use UUIDs to reduce the possibility of a collision but I would like to protect myself by using conditional saves. </p>
  
  <p>I came across <a href="http://java.awsblog.com/post/Tx1JADUVTWF7SP2/Specifying-Conditional-Constraints-with-Amazon-DynamoDB-Mapper" rel="noreferrer">this article</a> that uses <a href="http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/datamodeling/DynamoDBSaveExpression.html" rel="noreferrer">DynamoDBSaveExpression</a> however I'm not able to specify that the condition is "hashkey AND rangekey" cannot exist. The <a href="http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/services/dynamodbv2/datamodeling/DynamoDBSaveExpression.html" rel="noreferrer">API</a> specifies a <code>withConditionalOperator</code> method but I'm not able to see this in my class. I am using the latest aws java sdk also from <a href="http://mvnrepository.com/artifact/com.amazonaws/aws-java-sdk/1.9.15" rel="noreferrer">here</a>.</p>
  
  <p>Any suggestions on how to conditionally save? Or what I may be doing incorrectly?</p>