title: Linq filter builder not accepting lambda for filter type IN
body: <p>Basically what I'm trying to do is a deleteMany based on a list of items that I have using C# and linq for a mongoDB.</p>
  <p>This is my code:</p>
  <pre><code>// List of elements to delete, read from the POST request   
  string jsonBoletines = await new StreamReader(req.Body).ReadToEndAsync();
  
  // Convert the JSON into a list of &quot;Boletin&quot; objects, which is the type of objects I want //to delete from the collection 
  List &lt;Boletin&gt; boletinesToDelete = JsonConvert.DeserializeObject&lt;List&lt;Boletin&gt;&gt;(jsonBoletines);
  
  // Create the filter using IN, I'm trying to delete using the _id
  var filter = Builders&lt;Boletin&gt;.Filter.In(item =&gt; item._id, boletinesToDelete);
  
  var results = collection.DeleteMany(filter);
  </code></pre>
  <p>My code will not compile because on the lambda inside the IN filter shows this error:</p>
  <pre><code>var filter = Builders&lt;Boletin&gt;.Filter.In(item =&gt; item._id, boletinesToDelete);
  </code></pre>
  <blockquote>
  <p>CS1660: Cannot convert lambda expression to type X because it is not a delegate type</p>
  </blockquote>
  <p>Did some research and the error is supposed to be &quot;This error occurs if you try to assign or otherwise convert an anonymous method block to a type which is not a delegate type&quot;. But I'm not sure I get it since I'm not that familiar with delegate type</p>
  <p>Please help</p>