CODEWITHSUNDEEP
c#.netlibrary-design
VansFannel
VansFannel

Reputation: 45921

What would you do here? Return a null or throw an exception (framework design guides)

I'm developing a C# .NET Framework 4.0 library.

I have this code:

public static byte GetBatchStatus(string connString)
{
    if (string.IsNullOrEmpty(connString))
        throw new ArgumentNullException("connString");

    byte status;

    using (System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(connString))
    {
        conn.Open();

        SqlCommand cmd = new SqlCommand();

        cmd.CommandText = GetBatchStatusValueSQL;
        cmd.CommandType = CommandType.Text;
        cmd.Connection = conn;

        object o = cmd.ExecuteScalar();
        // Throws an ArgumentNullException if o is null.
        if (o == null)
            throw new ArgumentNullException("o");

        status = Convert.ToByte(o);
    }

    return status;
}

cmd.ExecuteScalar(); could return a null, but Convert.ToByte(o); returns 0.

If cmd.ExecuteScalar(); returns null its an error, because the value I'm looking for must be on database. If that value is not on database is an error.

What would you do here? Return a null or throw an exception?

Upvotes: 0

Views: 176

Answers (4)

Marco Alves
Marco Alves

Reputation: 2856

According to here http://msdn.microsoft.com/en-us/library/ms229009(v=vs.110).aspx and here http://msdn.microsoft.com/en-us/library/ms229030(v=vs.110).aspx exceptions are very expensive and should be used with care.

I surely would use return Convert.ToByte(o) and test it on the calling function.

Upvotes: 0

Mehul Vaghela
Mehul Vaghela

Reputation: 478

I think if you want to do something if cmd.ExecuteScalar() returns null then you should return a null. But as you said

the value I'm looking for must be on database. If that value is not on database is an error.

then you should throw an exception type of InvalidOperationException rather than ArgumentNullException.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1500525

If that value is not on database is an error.

An error in terms of "my belief system about the state of the system has been violated" or "the input must be invalid somehow"? It sounds like it's more the former - so I'd throw an exception. It sounds like the caller can't reasonably continue in this case. If they can, that's a different matter.

You might want to use InvalidOperationException, or perhaps create your own exception (InvalidDatabaseStateException for example) given that it's not really the state of this object which is invalid.

Upvotes: 0

Jevgeni Geurtsen
Jevgeni Geurtsen

Reputation: 3133

You are pretty much answering your own question:

because the value I'm looking for must be on database. If that value is not on database is an error.

If your program doesn't function without that value you should throw an exception, if not you can return null and make the user of the library decide what to do next.

Upvotes: 8

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