losing data when transfering SqlDataReader object to the method that needs IDataReader interface

Question

I have a method which needs a SqlDataReader object as parameter, and i have tests where i've mocked that object, and everything worked fine.

But, now i need to change that method. It should now only call new method, which has a IDataReader as parameter, and thats a problem, because, when I'm transfering the mocked SqlDataReader as a parameter of new method, it's losing his data, and i don't know why.

Something like this:

void method(SqlDataReader mockedObject)
{
   // example property
   mockedObject.FieldCount; // for example the value is 1;
   newMethod(mockedObject);
}

void newMethod(IDataReader newObject)
{
   // example property
   newObject.FieldCount // here value is 0;
}

I observed that if i'm only copying the SqlDataReader object to the new variable of type IDataReader, data also are cleared.

Something like this:

void method(SqlDataReader mockedObject)
{
   IDataReader variable = mockedObject;
}

the proper code:

=========================================================================================
        [TestMethod()]
    [DeploymentItem("IICMS.dll")]
    public void CheckNullableDateTimeTest_SqlDataReader_Valid()
    {
        MockRepository mocks = new MockRepository();
        SqlDataReader reader = mocks.DynamicMock<SqlDataReader>();
        string column = "test";
        DateTime? expected = new DateTime(2, 1, 1);
        Nullable<DateTime> actual;

        reader.Stub(r => r[column]).Return(expected);
        reader.Stub(r => r.FieldCount).Return(1);
        mocks.ReplayAll();

        actual = Utility_Accessor.CheckNullableDateTime(reader, column);
        Assert.AreEqual(expected, actual);
    }
======================================================================================
        public static DateTime? CheckNullableDateTime(SqlDataReader read, string column)
    {
        return GetValue<DateTime?>(read, column, null);
    }
======================================================================================
public static T GetValue<T>(IDataReader reader, string columnName, T defaultValue)
    {
        try
        {
            for (int i = 0; i < reader.FieldCount; i++)
            {
                if (reader.GetName(i) == columnName)
                {
                    object value = reader[i];
                    return Convert.IsDBNull(value) ? defaultValue : (T)value;
                }
            }

            return defaultValue;
        }
        catch
        {
            return defaultValue;
        }
    }

So there's the code, the second and the third method are in other dll but it doesn't have impact on anything. Object are mocked in RhinoMocks ;)

Data are losing after transfering SqlDataReader object (read) to GetValue method (i.e. FieldCount equals 0, in Check.. method it has proper value = 1)

Answer 1

I can't explain this but changing test method to the form below, makes, that all object fields are aviable in each method (CheckNullString and GetValue):

    [TestMethod()]
    [DeploymentItem("IICMS.dll")]
    public void CheckNullableDateTimeTest_SqlDataReader_Valid()
    {
        MockRepository mocks = new MockRepository();
        SqlDataReader reader = mocks.DynamicMock<SqlDataReader>();
        IDataReader reader2 = reader;
        string column = "test";
        DateTime? expected = new DateTime(2,1,1);
        DateTime? actual;

        reader.Stub(r => r[column]).Return(invalidValue);
        reader.Stub(r => r[0]).Return(invalidValue);
        reader.Stub(r => r.FieldCount).Return(1);
        reader.Stub(r => r.GetName(0)).Return(column);

        reader2.Stub(r => r[column]).Return(invalidValue);
        reader2.Stub(r => r[0]).Return(invalidValue);
        reader2.Stub(r => r.FieldCount).Return(1);
        reader2.Stub(r => r.GetName(0)).Return(column);
        mocks.ReplayAll();

        actual = Utility_Accessor.CheckNullString(reader, column);
        Assert.AreEqual(expected, actual);
    }