title: How to check a string exist in string set in dynamodb
body: <p>I have a string set in each item in my table. For example,</p>
  
  <pre><code>{                                        
     Title = "Book 101 Title"
     ISBN = "111-1111111111"
     Authors = "Author 1"
     Price = -2
     Dimensions = "8.5 x 11.0 x 0.5"
     PageCount = 500
     Color = [ "Red", "Black" ]
     ProductCategory = "Book" 
  }
  
  
  {                                        
     Title = "Book 102 Title"
     ISBN = "222-222222222"
     Authors = "Author 2"
     Price = -8
     Dimensions = "8.5 x 11.0 x 0.5"
     PageCount = 700
     Color = [ "Red", "Green" ]
     ProductCategory = "Book" 
  }
  </code></pre>
  
  <p>With dynamoDB php sdk, I want to get items which is "Red" color. I try like this.</p>
  
  <pre><code>$response = $client-&gt;query(array(
      "TableName" =&gt; $tablename,
      "KeyConditions" =&gt; array(
          "ComparisonOperator" =&gt; ComparisonOperator::CONTAINS,
          'Color' =&gt; array(
              'AttributeValueList' =&gt; array(
                  array(Type::STRING_SET =&gt; array("Red"))
          ),
       )
  ));
  </code></pre>
  
  <p>But I got an error like that.</p>
  
  <pre><code>ValidationException: One or more parameter values were invalid: ComparisonOperator CONTAINS is not valid for SS AttributeValue type
  </code></pre>