InvalidCastException in a LINQ query

Question

For this LINQ query I'm getting the exception below:

(from row in ds.Tables[0].AsEnumerable()
 where row.Field<string>("Dept_line_code") == DeptCode &&
 row.Field<string>("Skill_Name") == skill &&
 row.Field<string>("Acct_Code") == account && row.Field<string>("Location") == dtNewTable.Rows[intRow]["Location"].ToString()
 select row.Field<int>("Presently_Available") == null ? 0 : row.Field<int>("Presently_Available")
).FirstOrDefault();

Exception information:

Exception type: InvalidCastException

Exception message: Cannot cast DBNull.Value to type 'System.Int32'. Please use a nullable type.

I don't know nullable type and I'm not getting how to use nullable type to overcome this exception.

Priscilapriscilla

Briefly: by default, primitive types (such as int, double, float, ...) can't be assigned null values. The solution to this problem is to use a nullable type instead (like int?), which is really just a wrapper around the primitive type. – Selvage

Seems that you use DataSet, probably filled by DataAdapter. Then you can fill not a DataSet but a DataTable, if you're sure that resulting query contains only the single table. – Cohlette

When we need to use nullable types? what scenarios? why we have to use the same? Need information about the purpose and Pros or Cons with NUllable types? – Priscilapriscilla

@sukumar Google "nullable types C#" and read about it. You need to learn how to research your own issues rather than asking people to give you answers. – Selvage

Answer 1

you have to make int accept null value => int?

row.Field<int?>("Presently_Available") == null ? 0 : row.Field<int>("Presently_Available") ;

and this is a link for the Nullable Types

Blatant

You should probably give a link or a brief explanation of nullable types in your answer. The OP isn't going to understand why int? fixes his problem. – Selvage

Wow, a couple hours of searching to find out I just needed a question mark! – Didactic

Answer 2

select row.Field<int?>("Presently_Available")

Cohlette

Answer 3

change row.Field<int> to row.Field<int?>

Thirtyone