Question

i’m calling a function that throws a custom exception:

GetLockOwnerInfo(...)

This function in turn is calling a function that throws an exception:

GetLockOwnerInfo(...)
   ExecuteReader(...)

This function in turn is calling a function that throws an exception:

GetLockOwnerInfo(...)
   ExecuteReader(...)
      ExecuteReader(...)

And so on:

GetLockOwnerInfo(...)
   ExecuteReader(...)
      ExecuteReader(...)
         ExecuteReaderClient(...)
             Fill(...)

One of these functions throws an SqlException, although that code has no idea what an SqlException is.

Higher levels wrap that SqlException into another BusinessRuleException in order to include some special properties and additional details, while including the “original” exception as InnerException:

catch (DbException ex)
{
    BusinessRuleExcpetion e = new BusinessRuleException(ex)
    ...
    throw e;
}

Higher levels wrap that BusinessRuleException into another LockerException in order to include some special properties and additional details, while including the “original” exception as InnerException:

catch (BusinessRuleException ex)
{
    LockerException e = new LockerException(ex)
    ...
    throw e;
}

The problem now is that i want to catch the origianl SqlException, to check for a particular error code.

But there’s no way to “catch the inner exception”:

try
{
   DoSomething();
}
catch (SqlException e)
{
   if (e.Number = 247) 
   {
      return "Someone";
   }
   else
      throw;
}

i thought about catching SqlException right when it’s thrown, and copy various values to the re-thrown exception – but that code is not dependant on Sql. It is experiencing an SqlException, but it has no dependency on SqlException.

i thought about catching all exceptions:

try
{
   DoSomething(...);
}
catch (Exception e)
{
   SqlException ex = HuntAroundForAnSqlException(e);
   if (ex != null)
   {
      if (e.Number = 247) 
      {
          return "Someone";
      }
      else
         throw;
   }
   else
      throw;
}

But that’s horrible code.

Given that .NET does not let you alter the Message of an Exception to include additional information, what is the intended mechanism to catch original exceptions?

Answer 1

I hate to have to tell you this, but you cannot catch an inner exception.

What you can do is inspect one.

I suggest you catch your high-level exception (I believe it was LockerException) and inspect the InnerException property of that exception. Check the type, and if it’s not a SqlException, check the InnerException of that exception. Walk each one until you find a SqlException type, then get the data you need.

That said, I agree with dasblinkenlight that you should consider — if possible — a heavy refactor of your exception framework.