title: Filling in missing values basing on another list of int
body: <p>I have a IEnumerable where the model of the SaleReport is as follow:</p>
  
  <pre><code>    public int ID { get; set; }
      public DateTime StartDate { get; set; }
      public DateTime EndDate { get; set; }
      public decimal Amount { get; set; }
      public SalesReportProduct Product { get; set; }
      public int ItemID { get; set; }
      public int LanguageID { get; set; }
      public int ProductID { get; set; }
  </code></pre>
  
  <p>I am filling this IEnumerable with db entries based on dateTime values:</p>
  
  <pre><code>salesReports = _salesReport.GetAll(fromDate, toDate);
  </code></pre>
  
  <p>Then I have a list of int that are all the available ItemID:</p>
  
  <pre><code>var ItemIDList = new List&lt;int&gt;();
  </code></pre>
  
  <p>My problem is that I have to insert all the SalesReport with ItemID that is not in the IEnumerable, so for each of the value of the ItemIDList I check if there is at least one corresponding ItemID in the IEnumerable, if not I have to append a new SalesReport with that ItemID.</p>
  
  <p>How can I do this easily? </p>