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How do I Evaluate Null value from database?

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How do I Evaluate Null value from database?

Mar 13th, 2008

I have been looking for a way to evaluate if a column in a database has a null value in it. So far, every method suggested have failed and I would like to know anyone else have successfully evaluate a null value in C# Visual Studio 2005.

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Re: How do I Evaluate Null value from database?

Mar 13th, 2008

you can use nullable types i.e. - int? myVar = ... ;

you can also check to see if the value is = to System.DbNull...

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

How exactly do I do that, I've use IsDBNull, Convert.IsDBNull, IsDBNull.Value and nothing works and I've tried type casting. ????

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

The following can help you but i am sure whether this is the right way.

While selecting the column check for null values like

select ISNULL(class,-1) from student

If the column class contains null values,the query returns -1 value.
Using this value you can identity the column contains null value.

Good Luck.

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

You need to compare the column value with System.DBNull.Value

So assuming a DataTable for example:

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if( myDataTable.Rows[0]["someColumn"].Equals(System.DBNull.Value) )
{
          //Handle situation for null value.
}
if( myDataTable.Rows[0]["someColumn"].Equals(System.DBNull.Value) )
{
          //Handle situation for null value.
}

Last edited by hollystyles; Mar 14th, 2008 at 5:59 am.

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

I tried that method already and it does not work.

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

Hmm... well it works for me. You'll have to post some code or give more information.

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

you can also get the value of the cell and use .text.tostring
then test the length of the string len(abc) > 0

--
"Dummy."

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Re: How do I Evaluate Null value from database?

Mar 14th, 2008

Here is the code

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[WebMethod]
    public int TestDBNullValue(string PID)
    {
        int ErrorValue = 0;
        if (PID.Equals(String.Empty))
        {
            ErrorValue = 10110; //PID is null or empty
        }
        else
        {
            DeviceTableAdapter DeviceAdapter = new DeviceTableAdapter();
            JeanPierre.DeviceDataTable DeviceTable = DeviceAdapter.GetDeviceUIDByPID(PID);
 
            if (DeviceTable.Count.Equals(0))
            {
                ErrorValue = 1111; //No device found
            }
            else
            {
                JeanPierre.DeviceRow DevRows = DeviceTable[0];
 
                if(DevRows.TrackingMode.Equals(System.DBNull.Value))
                {
                    ErrorValue = 1;
                }
                else
                {
                    ErrorValue = 41;
                }
            }
        }
        return (ErrorValue);
    }
[WebMethod]
    public int TestDBNullValue(string PID)
    {
        int ErrorValue = 0;
        if (PID.Equals(String.Empty))
        {
            ErrorValue = 10110; //PID is null or empty
        }
        else
        {
            DeviceTableAdapter DeviceAdapter = new DeviceTableAdapter();
            JeanPierre.DeviceDataTable DeviceTable = DeviceAdapter.GetDeviceUIDByPID(PID);

            if (DeviceTable.Count.Equals(0))
            {
                ErrorValue = 1111; //No device found
            }
            else
            {
                JeanPierre.DeviceRow DevRows = DeviceTable[0];

                if(DevRows.TrackingMode.Equals(System.DBNull.Value))
                {
                    ErrorValue = 1;
                }
                else
                {
                    ErrorValue = 41;
                }
            }
        }
        return (ErrorValue);
    }