What Exception should be thrown when an ADO.NET query cannot retrieve the requested data?

Question

In an attempt to add some parameter validation and correct usage semantics to our application, we are trying to add correct exception handling to our .NET applications.

My question is this: When throwing exceptions in ADO.NET if a particular query returns no data or the data could not be found, what type of exception should I use?

Psuedocode: (read, don't scrutinize the semantics of the code, I know it won't compile)

public DataSet GetData(int identifier)
{
    dataAdapter.Command.Text = "Select * from table1 Where ident = " + identifier.toString();
    DataSet ds = dataAdapter.Fill(ds);
    if (ds.table1.Rows.Count == 0)
        throw new Exception("Data not found");

    return ds;
}

Answer 1

As far as ADO.net is concerned, a query that returns zero rows is not an error. If your application wishes to treat such a query as an error, you should create your own exception class by inheriting from Exception.

public class myException : Exception
{
   public myException(string s) : base() 
   {
      this.MyReasonMessage = s;
   }
}

public void GetData(int identifier)
{
    dataAdapter.Command.Text = "Select * from table1 Where ident = " + identifier.toString();
    DataSet ds = dataAdapter.Fill(ds);
    if (ds.table1.Rows.Count == 0)
        throw new myException("Data not found");
}

Answer 2

You really should define your own exception : DataNotFoundException.

You should not use the basic class Exception, since when you will catch it in calling code, you will write something like

try
{
     int i;
     GetData(i);

}
catch(Exception e) //will catch many many exceptions
{
    //Handle gracefully the "Data not Found" case;
    //Whatever else happens will get caught and ignored
}

Where as catching only your DataNotFoundEXception will get only the case you really want to handle.

try
{
     int i;
     GetData(i);

}
catch(DataNotFoundException e) 
{
    //Handle gracefully the "Data not Found" case;
} //Any other exception will bubble up

There is a class aptly named SqlException, when there are troubles with the SQL engine but it's better not overload it with your business logic

Answer 3

The MSDN guidelines state:

• Consider throwing existing exceptions residing in the System namespaces instead of creating custom exception types.

• Do create and throw custom exceptions if you have an error condition that can be programmatically handled in a different way than any other existing exceptions. Otherwise, throw one of the existing exceptions.

• Do not create and throw new exceptions just to have your team's exception.

There is no hard and fast rule: but if you have a scenario for treating this exception differently, consider creating a custom exception type, such as DataNotFoundException as suggested by Johan Buret.

Otherwise you might consider throwing one of the existing exception types, such as System.Data.DataException or possibly even System.Collections.Generic.KeyNotFoundException.

Answer 4

just a bit note: IF POSSIBLE,consider possibility don't use exceptions,but error codes instead. this will increase youre performance.