title: dynamic linq query
body: <p>If I have Book entity with properties Id, Title, ISBN, Tag. Inside winform window user can input search text and from combobox choose ByTitle, ByISBN, ByTag search options.</p>
  
  <p>on button click event those values are taken as</p>
  
  <pre><code>var comboSelection = (comboBox1.SelectedItem ?? "").ToString();
  var searchText = txtSearchText.Text;
  </code></pre>
  
  <p>now I want to grab values from my repository using these values. I already have repository.GetBooks() which returns IEnumerable of books.</p>
  
  <p>My question is how to define query with where clause having combo selection in mind.</p>
  
  <pre><code>var result = repository.GetBooks().Where(x=&gt;x. ....)
  </code></pre>
  
  <p>obviously if ByTag is selected than this query should be <code>.Where(x=&gt;x.Tag==comboSelection)</code></p>