title: Condition Expression for UpdateItem exceeding max
body: <p>I have a Condition on my updateItem call that is exceeding the defined max. When I run this, I will ultimately have a value of 101. Is there a way to ensure that the Conditional Expression checks the <strong><em>final value</em></strong> of the Update to prevent it from exceeding 100? Note that in my test, I increment by 1, but ultimately I will increment by arbitrary values.</p>
  
  <pre><code>$query = array(
    'TableName'         =&gt; $this-&gt;table_name,
    'Key'               =&gt; $this-&gt;get_query_key($obj),
    'ConditionExpression'   =&gt; 'num_completed &lt;= :max',
    'UpdateExpression'      =&gt; 'SET num_completed = num_completed + :num',
    'ExpressionAttributeValues' =&gt; array(
      ':num' =&gt; array('N' =&gt; 1),
      ':max' =&gt; array('N' =&gt; 100)
    )
    //'ReturnConsumedCapacity' =&gt; 'TOTAL'
  );
  try {
    $this-&gt;dynamo_db-&gt;updateItem($query);
  }
  </code></pre>