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Checking for DBNull throws a StrongTypingException

I am using a dataset to pull data from a DB. One of the fields in a row is NULL. I know this. However, the following vb.net code throws a StrongTypingException (in the autogenerated get_SomeField() method in the dataset designer):

If Not IsDBNull(aRow.SomeField) Then
'do something
End If

According to documentation and this question it should be fine.

edit: If aRow.SomeField is DBNull.Value Then also returns the same error. Argh.

Solution

  • The difference is that in the related question it is talking about an untyped value (i.e. object) via an indexer. When you go via .SomeField, the type is already included - so this could be int etc. And it wouldn't make sense to try IsDBNull on an int, as an int can never be DBNull.

    Essentially the SomeField is a wrapper for (excuse the C# accent...)

    public int SomeField {
    get { return (int) this["someFieldName"]; }
    set { this["someFieldName"] = value; }
}

    I'm not a huge DataTable person, but you could try checking it by name/index/column; or marking the column as nullable so that it is Nullable<int> (in the example above).