How to handle DBNull exception for multiple values

Question

I am assigning values to a model. Some of these values can be null. I have tried several methods to handle DBNull values but still getting errors

 dPbtbud.Xfer = dataFromFile.Tables[0].Rows[i][j++] == DBNull.Value ? 
      0.0 : 
      Convert.ToDouble(dataFromFile.Tables[0].Rows[i][j++]);

Also tried

 dPbtbud.Xfer = dataFromFile.Tables[0].Rows[i][j++] is DBNull ? 
     0.0 : 
     Convert.ToDouble(dataFromFile.Tables[0].Rows[i][j++]);

Non seem to handle null values

Have you tried: `dataFromFile.Tables[0].Rows[i][j++] == null`? — Stefan, Jul 12 '19 at 21:09
@Stefan Yeah just tried. Getting same error "Object cannot be cast from DBNull to other types" — masksoverflow, Jul 12 '19 at 21:14
Where is this data coming from? It looks like it has been read from a file. Is it string data? Than it should be `string.IsNullOrWhiteSpace(dataFromFile.Tables[0].Rows[i][j++]) ? 0.0 : ..` — Stefan, Jul 12 '19 at 21:16
Unless, it's value is actual `"NULL"` or `"NILL"` or something like that. — Stefan, Jul 12 '19 at 21:16
Possible duplicate of [Object cannot be cast from DBNull to other types](https://stackoverflow.com/questions/6098646/object-cannot-be-cast-from-dbnull-to-other-types) — Fabio, Jul 12 '19 at 21:21
Tried that as well...Yeah the data is coming from an excel file exported to a dataset — masksoverflow, Jul 12 '19 at 21:22
@Fabio except I have tried that soln in that question as you can see and still having problems — masksoverflow, Jul 12 '19 at 21:23
@Fabio I scaffolded the model from a database, messing with the nullability won't mess with the database? — masksoverflow, Jul 12 '19 at 21:26
@masksoverflow, can you please add to the question what you tried and what "_Non seem to handle null values_" mean in your tries, what exception you get for example. — Fabio, Jul 12 '19 at 21:27
@masksoverflow, if column in database is nullable then should be ok. — Fabio, Jul 12 '19 at 21:28
@Fabio I can't do if and else on it. As in if(!(dataFromFile.Tables[0].Rows[i][j++]) is DBNull)) Because I am doing this for a couple of values and its going to get really ugly — masksoverflow, Jul 12 '19 at 21:31
You realise that the `j++` executes up to twice, right? So when it is not null, you are fetching the next row (which now may be null). — GSerg, Jul 12 '19 at 21:32
Since `Xfer` is nullable double, just do `dPbtbud.Xfer = dataFromFile.Tables[0].Rows[i].Field[j++]` — Fabio, Jul 12 '19 at 21:35
@GSerg Yeah I do realize that. But I think you may be right as in its looking for a value that may now be null — masksoverflow, Jul 12 '19 at 21:43

score 0 · Accepted Answer · answered Jul 12 '19 at 21:52

My suggestion is to create an extension method to check null and DBNull :

namespace Helper
{
 public static class ConvertEX1
    {
        public static object IsNull<T>(this object obj, T def) where T : struct
        {
            if (obj == null || obj == DBNull.Value)
                return (T)Convert.ChangeType(def, typeof(T));
            return (T)Convert.ChangeType(obj, typeof(T));
        }
    }
}

Don't forget to import the namespace in every .cs file you use your function:

using Helper;
...


dPbtbud.Xfer = (double)dataFromFile.Tables[0].Rows[i][j++].IsNull(0.0);

This extension is redundant for OP case, `DataRow` already has extension method `.Field` which will return correct type. — Fabio, Jul 13 '19 at 09:28

How to handle DBNull exception for multiple values

1 Answers1