title: Unable to cast object of type 'System.Decimal' to type 'System.String'
body: <p>I wrote this code to find which one of dtExistCosts doesn,y exit in costsList.</p>
  
  <pre><code>var costMustbeDeleteDt = (
          from e in dtExistCosts.AsEnumerable()
          where !(from c in costsList 
                  select Convert.ToString(c.CostRecordId))
                              .Contains(e.Field&lt;string&gt;("DETAIL_HAZ_PK"))
          select e).CopyToDataTable();
  </code></pre>
  
  <p>but when I run it I get the error: </p>
  
  <blockquote>
    <p>Unable to cast object of type <code>System.Decimal</code> to type <code>System.String</code></p>
  </blockquote>
  
  <p>in </p>
  
  <pre><code>!(from c in costsList 
    select Convert.ToString(c.CostRecordId))
          .Contains(e.Field&lt;string&gt;("DETAIL_HAZ_PK"))
  </code></pre>
  
  <p>why?</p>