Conversion Problem

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shapper - 12 Oct 2007 17:06 GMT

Hi,

I am trying to fill a Generic.List(Of MyClass) with a dataset row
values taken from an MSSQL database:

For Each drPost As DataRow In dsPosts.Tables(0).Rows

Dim post As New Post

With post
.AverageRating = Convert.ToDouble(drPost("PostAverageRating"))
.IsPublished = Convert.ToBoolean(drPost("PostIsPublished"))
.NumberOfComments =
Convert.ToInt32(drPost("PostNumberOfComments"))
.PostId = New Guid(Convert.ToString(drPost("PostId")))
.Title = Convert.ToString(drPost("PostTitle"))
.UpdatedDate = Convert.ToDateTime(drPost("PostUpdatedDate"))
End With

posts.Add(post)

Next drPost

Some of the rows might have empty fields.

I am having an error right on the first conversion (AverageRating):

Object cannot be cast from DBNull to other types.

What am I doing wrong?

Thanks,

Miguel

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gnewsgroup - 12 Oct 2007 17:11 GMT

> Hi,
>
[quoted text clipped - 30 lines]
>
> Miguel

The exception message has told you: Object cannot be cast from DBNull
to other types. drPost("PostAverageRating") is null, and you cannot
convert a null to a double. You gotta investigate why
drPost("PostAverageRating") is null.

Reply to this Message

shapper - 12 Oct 2007 17:15 GMT

> > Hi,
>
[quoted text clipped - 35 lines]
> convert a null to a double. You gotta investigate why
> drPost("PostAverageRating") is null.

But the point is that some of the records might have null fields. So
if a field is null the correspondent class property would become
Nothing.
Are you saying that for each conversion i need to check if
drPost(.......) is null and make the conversion just after it?

Isn't there a straight forward way to give the Nothing value to class
property when drPost(.......) is null?

Thanks,
Miguel

Reply to this Message

gnewsgroup - 12 Oct 2007 17:24 GMT

> > > Hi,
>
[quoted text clipped - 47 lines]
> Thanks,
> Miguel

First of all, I think it is suggested that we always check if it is a
null before we attempt to use the value.

Second, converting a null to a Double simply does not happen.

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Peter Bromberg [C# MVP] - 12 Oct 2007 17:27 GMT

just test the item for IsDbNull or =DbNull.Value. If it is, you can give the
property say a default value of zero and no exception will be thrown.
-- Peter
Recursion: see Recursion
site: http://www.eggheadcafe.com
unBlog: http://petesbloggerama.blogspot.com
BlogMetaFinder: http://www.blogmetafinder.com

> > > Hi,
> >
[quoted text clipped - 47 lines]
> Thanks,
> Miguel

Reply to this Message

bruce barker - 12 Oct 2007 19:18 GMT

thats correct.

in .net value types like double, int, date, etc, do not support null
(nothing) as value, so a function returning a double, can not return null.

-- bruce (sqlwork.com)

>>> Hi,
>>> I am trying to fill a Generic.List(Of MyClass) with a dataset row
[quoted text clipped - 34 lines]
> Thanks,
> Miguel

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