Check for database value not working because of null value in database

Question

I am trying to perform a delete but I need to make sure that a value is present before trying to delete. The value is pulled from the database. I need to check for dbnull. If it's not, then the delete can go ahead. I have tried the following but it does not work:

if (!DBNull.Value.Equals(x.ColourImage))
{
    File.Delete(HttpContext.Current.Server.MapPath(x.ColourImage));
}

When I try I get the following exception:

Inner Exception Type: System.InvalidCastException
Unable to cast object of type 'System.DBNull' to type 'System.String'.
Inner Source: App_Code.bvtnyzaw
Inner Stack Trace:
at Products.GetAllProdColoursRow.get_ColourImage() in c:\Users\micha\AppData\Local\Temp\Temporary ASP.NET Files\vs\d9cd3740\a9faac06\App_Code.bvtnyzaw.2.cs:line 2245

Exception Type: System.Data.StrongTypingException
Exception: The value for column 'ColourImage' in table 'GetAllProdColours' is DBNull.

****EDIT**** I have already seen the suggested question but none of those solutions seemed to help. No matter what I try I get the same exception.

**** My complete code using the suggested answer but still I get the same exception ****

public bool DeleteProductColour(int colid, int prd)
{
    bool prodColourDeleted = false;
    try
    {
        var x = pcAdp.GetAllProdColours(prd).AsEnumerable().Where(y => y.ColourId == colid).First();

        if (x != null && !string.IsNullOrEmpty(x.ColourImage))
        {
            File.Delete(HttpContext.Current.Server.MapPath(x.ColourImage));
        }
        pcAdp.DeleteProductColour(colid);
        prodColourDeleted = true;
    }
    catch(Exception er)
    {
        ExceptionUtility.LogException(er, "Delete product colour - ProductsBLL");
    }
    return prodColourDeleted;
}

* UPDATE *

I have tried the following but I get an exception: public bool DeleteProductColour(int colid, int prd) { bool prodColourDeleted = false; try { var x = pcAdp.GetAllProdColours(prd).ToList();

        if (x.Any())
        {
            var colour = x.Where(y => y.ColourId == colid).FirstOrDefault();

            if (colour != null && !string.IsNullOrEmpty(colour.ColourImage))
            {
                File.Delete(HttpContext.Current.Server.MapPath(colour.ColourImage));
            }
        }
        pcAdp.DeleteProductColour(colid);
        prodColourDeleted = true;

    }
    catch (Exception er)
    {
        ExceptionUtility.LogException(er, "Delete product colour - ProductsBLL");
    }
    return prodColourDeleted;

}

The exception I get is

'product.ColourImage' threw an exception of type 'System.Data.StrongTypingException'

Ive tried those suggestions but it does not seem to be making any difference. — M_Griffiths, Jun 02 '18 at 08:23
you did look at https://stackoverflow.com/questions/870697/unable-to-cast-object-of-type-system-dbnull-to-type-system-string ? — Thomas Ayoub, Jun 02 '18 at 22:26
Yes but it doesn't seem to be working. I think I am just going to add a default value to the column and check for that value instead. — M_Griffiths, Jun 03 '18 at 12:47

Murat Can OĞUZHAN · Answer 1 · 2018-06-02T09:16:32.337

0

use

if(!string.IsnullOrEmpty(x.ColourImage)){}

if still getting error you are need to check x is null or is not null;

if(x!=null&&!string.IsnullOrEmpty(x.ColourImage)){}

Or another option would work is;

if(x.ColourImage!= DBNull.Value){}

//I think this method mmight be work

 public bool DeleteProductColour(int colid, int prd)
    {
        bool prodColourDeleted = false;
        try
        {
            var x = pcAdp.GetAllProdColours(prd).AsEnumerable().Where(y => y.ColourId == colid).FirstOrDefault();

            if (x != null && !string.IsnullOrEmpty(x.ColourImage))
            {
                File.Delete(HttpContext.Current.Server.MapPath(x.ColourImage));
            }
            pcAdp.DeleteProductColour(colid);
            prodColourDeleted = true;
        }
        catch(Exception er)
        {
            ExceptionUtility.LogException(er, "Delete product colour - ProductsBLL");
        }
        return prodColourDeleted;
    }

edited Jun 02 '18 at 09:16

answered Jun 02 '18 at 08:40

Murat Can OĞUZHAN

735
11
19

Thank you for your suggestions but unfortunately I am still getting the same exception. I have updated the question to include the complete code with your suggestion incorporated. – M_Griffiths Jun 02 '18 at 08:52
Can you try FirstOrDefault instead of First() @M_Griffiths – Murat Can OĞUZHAN Jun 02 '18 at 08:54
It gave the following error: Operator '!=' cannot be applied to operands of type 'string' and 'System.DBNull' – M_Griffiths Jun 02 '18 at 09:03
ok that portion convert again to !string.IsNullOrEmpty() @M_Griffiths – Murat Can OĞUZHAN Jun 02 '18 at 09:16
That brought us back to: The value for column 'ColourImage' in table 'GetAllProdColours' is DBNull – M_Griffiths Jun 02 '18 at 09:21
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/172292/discussion-between-murat-can-oguzhan-and-m-griffiths). – Murat Can OĞUZHAN Jun 02 '18 at 09:37

score 0 · Accepted Answer · answered Jun 03 '18 at 18:14

0

In the strongly typed DataSet this kind of problem occurs.

Probably before filling your Dataset, get the respective DataColumn and set the DataColumn.AllowDBNull to true.

https://msdn.microsoft.com/en-us/library/system.data.datacolumn.allowdbnull(v=vs.110).aspx

answered Jun 03 '18 at 18:14

Pavan Chandaka

11,671
5
26
34

Thank you very much. I can't believe I missed that. – M_Griffiths Jun 04 '18 at 09:06

Check for database value not working because of null value in database

2 Answers2