title: how to use in operator in dynamo db
body: <p>I have a user table with a field username. I need to write something equivalent to this in dynamo db: Select * from user where username in('a','b','c');</p>
  
  <p>Adding more from code prosepective i have usernames in an array say var arr=['a','b','c'];</p>
  
  <p>I so far tried this which is giving me zero result</p>
  
  <pre><code>    this.dynamo.client.scanAsync({
          TableName: this.dynamo.table('users'),
          FilterExpression: 'username IN (:list)',
          ExpressionAttributeValues: {
              ':list': arr.toString()
          }
      }).then((response) =&gt; {
          console.log(response);
          return {
              userFriends: result.Item.friends
          };
      });
  </code></pre>
  
  <p>When I pass one element in array it give me result searching passed single element in user table but its not working with more than one element in array.</p>