Does SQL substitute float = 0 with DBNull.Value?

Hi
I have only been coding in .Net for about six months, and am not sure if this is a C# problem or an SQL one. I use the Data Access Application Block in my program.

I have two optional fields on my form (RangeFrom and RangeTo). If the user chooses not to enter data into these textboxes(textbox = ""), an entry on the db is created with null values. It works.

But sometimes the user wants to enter 0 as either an upper or lower end of a range. This is where my problem comes in. My program saves 0 as null too.

In my program I do a test on the textboxes and populate two float values in a business object (objQuestion) accordingly, like this:

if (txtrangefrom.Text != "") {
objQuestion.RangeFrom=float.Parse(txtrangefrom.Text);
objQuestion.RangeTo=float.Parse(txtrangeto.Text);
}
else {
objQuestion.RangeFrom=Convert.ToSingle(null);
objQuestion.RangeTo=Convert.ToSingle(null);
}

And this is what my Business object look like. It sets up the parameters and calls the Data Access Application Block to create an entry in my table:

// fieldslist
float cvintRangeFrom;
float cvintRangeTo;
//properties
public float RangeFrom {
get {
return cvintRangeFrom;
}
set {
cvintRangeFrom = value;
}
}
public float RangeTo {
get {
return cvintRangeTo;
}
set {
cvintRangeTo = value;
}
}
// some code deleted for readability...
public int AddOption() {
string cvstrSpName = "addOption";
SqlParameter [] cvstrStoredParams = SqlHelperParameterCache.GetSpParameterSet(gcstrConnectionString, cvstrSpName, true);
//lines deleted for readability...
//check if the optional fields have a value associated with them. if not, assign dbnull.value.
cvstrStoredParams[4].Value=(cvintRangeFrom != Convert.ToSingle(null) ? cvintRangeFrom : (object)DBNull.Value);
cvstrStoredParams[5].Value=(cvintRangeTo != Convert.ToSingle(null) ? cvintRangeTo : (object)DBNull.Value);
//lines deleted for readability...
SqlHelper.ExecuteNonQuery(gcstrConnectionString, CommandType.StoredProcedure, cvstrSpName, cvstrStoredParams);
return(cvintOptionID = Convert.ToInt32(cvstrStoredParams[0].Value));
}

I use Convert.ToSingle when working with nulls (or possible nulls) because I get an error when I use float.parse for this.

The thing is, after this method AddOption has been executed, I test the value if the business object's rangefrom (that is where I entered 0) and display it on my form. I still shows a 0, but on my database table it is null!

objQuestion.AddOption();
//txtrangefrom.Text=""; on the next line I test the value in the business object...
txtrangefrom.Text=objQuestion.RangeFrom.ToString(); // and this displays 0!!!
//txtrangeto.Text="";
txtrangeto.Text=objQuestion.RangeTo.ToString();

So to me it seems the problem seems to be either the DAAB or on the SQL side, but hopefully somebody can prove me wrong! I was thinking that it could also be float.parse/Convert.ToSingle methods and have done various tests, but I am none the wiser...
Any help or ideas will be greatly appreciated...I had this same problem with a VB project.

Just change the value of the floats to something that is not within the valid range (-1 or something) instead of null. It's not pretty or elegant, but it's better than fiddling with nulls ;)

SQLServer (I think) does implicitly convert 0 to null in some occasions, but I don't know the full details.

HTH|||You're right, it's not pretty, but I'll give it a go.
Thanks.