Implementing Business Logic - ASP.NET Dynamic Data - page 300

Obviously, a yellow page of death is not acceptable in a production-ready web
application, and you need to change it to report the error consistently with other valida-
tion results implemented in the application code. In particular, you need to catch the
appropriate exceptions and rethrow them wrapped inside of ValidationException
instances. Here is how you can override the SaveChanges method of the
NorthwindEntities class to do this:
public override int SaveChanges(SaveOptions options)
{
try
{
return base.SaveChanges(options);
}
catch (UpdateException e)
{
HandleSqlException(e);
throw;
}
}
The new version of the SaveChanges method puts the call to the base method inside of a
try/catch block to intercept database errors reported as instances of the UpdateException
class by the Entity Framework. The UpdateException itself provides a very generic error
message saying that an error has occurred when trying to save changes; however, the
underlying database error is still available through its InnerException property used in the
HandleSqlException method shown here:
private static void HandleSqlException(Exception e)
{
SqlException error = e.InnerException as SqlException;
if (error != null)
{
if (error.Number == 547)
HandleReferenceConstraintViolation(error);
else if (error.Number == 2627)
HandleUniqueKeyConstraintViolation(error);
}
}
In this example, Microsoft SQL Server is used, so the inner exception will be of type
SqlException defined in the System.Data.SqlClient namespace. You can determine what
kind of error has occurred by looking at the SQL error Number , which for the violation of a
UNIQUE KEY constraint will be 2627 and for a FOREIGN KEY violation will be 547 .