title: Entity Framework Core - Computed Column issue
body: <p>I have an entity class with a column called 'CalculatedId'. This column is obtained from an SQL statement and the column does NOT exist in the database table.</p>
  
  <p>If I run app I get an error telling me that the column does not exist. This error is due to the framework trying to map the column to a physical column.</p>
  
  <p>Below is my mapping code:</p>
  
  <pre><code> modelBuilder
      .Entity&lt;Widgets&gt;()
      .Property(x =&gt; x.CalculatedId)
      .HasComputedColumnSql("select top 1 Id from MyTable");
  </code></pre>
  
  <p>I thought that this would tell EF not to look for a physical column as it's generated.</p>
  
  <p>The only way I can get rid of the error is if I do this:</p>
  
  <pre><code> modelBuilder
      .Entity&lt;Widgets&gt;()
      .Ignore(x =&gt; x.CalculatedId);
  </code></pre>
  
  <p>Problem there is that the column is totally ignored an not generated at all.</p>
  
  <p>Can someone please connect the dots for me and clarify what needs to be done to make sure that the column is generated but EF does not look for it in the database.</p>
  
  <p><strong>NB:</strong> Has to be done in the fluent API, no data annotations.</p>