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Page Revision: Fri, Jan 17, 2020, 8:03 AM

Overview¶

This article outlines the steps to handle concurrency exceptions in Entity Framework 6.

Concurrency exceptions happen only on entities/tables that implement a row version field. They occur when EF detects that an underlying data record has changed since it was first retrieved. This frequently happens because two processes or users are trying to edit the record simultaneously.

References¶

• https://docs.microsoft.com/en-us/aspnet/mvc/overview/getting-started/getting-started-with-ef-using-mvc/handling-concurrency-with-the-entity-framework-in-an-asp-net-mvc-application
  

Implementation¶

Data Model¶

= The entity/table that we want to implement optimistic concurrency on must have a field similar to the following.

[Timestamp]
public byte[] RowVersion { get; set; }

Exception Handling and Retry Logic¶

var done = false;
var iterNum = 1;
var maxIterations = 5;

do
{
    try
    {

        LoggingEngine.Info($"Starting Iteration {iterNum}.");

        /*  TODO: Implement logic to update record. */

        db.SaveChanges();

        done = true;
    }
    catch (SqlException ex) when (ex.Number == 1205) // 1205 = deadlock victim
    {
        iterNum++;
        done = (iterNum >= maxIterations);
        if (done)
        {
            LoggingEngine.Exception($"Deadlock exception while trying to "
                + $"do stuff - iteration {iterNum}. EXITING!", ex);
        }
        else
        {
            LoggingEngine.Exception($"Deadlock exception while trying to "
                + $"do stuff - iteration {iterNum}. Retrying operation.", ex);
        }
    }
    catch (DbUpdateConcurrencyException ex)
    {
        iterNum++;
        done = (iterNum > maxIterations);

        if (done)
        {
            LoggingEngine.Exception($"Concurrency exception while trying to " 
                + $"do stuff - iteration {iterNum-1}. EXITING!", ex);
        }
        else
        {
            LoggingEngine.Exception($"Concurrency exception while trying to "
                + $"do stuff - iteration {iterNum-1}. Retrying.", ex);

            foreach (var en in ex.Entries)
            {
                en.Reload(); // RELOAD = database wins
            }
        }
    }
    catch (Exception ex)
    {
        done = true;
        LoggingEngine.Exception($"Exception while trying to do stuff", ex);
    }
} while (!done);