title: text index required for $text query error while search text in MongoDB
body: <p>I have a collection in MongoDB and I created an index on a filed as below:</p>
  
  <pre><code>var indexOptions = new CreateIndexOptions();
  var indexKeys = Builders&lt;Book&gt;.IndexKeys.Ascending(book=&gt; book.title);
  var indexModel = new CreateIndexModel&lt;Book&gt;(indexKeys, indexOptions);
  collection.Indexes.CreateOneAsync(indexModel);
  </code></pre>
  
  <p>After that I want to search a text in the collection as below:</p>
  
  <pre><code>var filter = Builders&lt;Book&gt;.Filter.Text(textToSearch);
  var result = collection.Find(filter).ToList(); // Error occurs here
  </code></pre>
  
  <p>But I get "Command find failed: text index required for $text query." error on the last line.</p>
  
  <p>Update:</p>
  
  <p>I created the index manually in <code>mongo</code> command line interface:</p>
  
  <pre><code>db.Book.createIndex({title:1})
  </code></pre>
  
  <p>but it didn't work. </p>