title: DynamoDB UpdateItem failed
body: <p>I am using DynamoDB Go SDK for CRUD operations. I verified <code>PutItem</code> and <code>GetItem</code> calls are working fine. However, when I use <code>UpdateItem</code> which updates some attributes, it fails. I narrowed it down to specific to an attribute that stores the current timestamp in epoch format.</p>
  
  <pre><code>    updateItem := &amp;dynamodb.UpdateItemInput{
          TableName:aws.String(tableName),
          ExpressionAttributeValues: map[string]*dynamodb.AttributeValue{
              ":r": {
                  S:aws.String("Renamed"),
              },
              ":rp": {
                  S: aws.String("RenamingParty"),
              },
              ":rr": {
                  S: aws.String("RenameReason"),
              },
              "rt": {
                  N: aws.String(strconv.FormatInt(time.Now().Unix(), 10)),
              },
          },
          Key: map[string]*dynamodb.AttributeValue{
              "pKey": {
                  S: aws.String(pKey),
              },
              "rKey": {
                  S:aws.String(rKey),
              },
          },
          ReturnValues:aws.String("ALL_NEW"),
          UpdateExpression:aws.String("set RenameStatus = :r, RenamingParty = :rp, RenameReason = :rr RenameTime = :rt"),
      }
  
      _, err := svc.UpdateItem(updateItem)
  </code></pre>
  
  <p><strong>Error returned</strong>:</p>
  
  <blockquote>
    <p>failed to update item: %v ValidationException: ExpressionAttributeValues contains invalid key: Syntax error; key: "rt"
        status code: 400, request id: </p>
  </blockquote>