LINQ CopyToDataTable -- Cannot cast DBNull.Value to type 'System.Decimal'. Please use a nullable type

Question

I am parsing two Excel files that contain many fields, most importantly TOTAL_DOLLARS and TOTAL_UNITS fields, that often have values, but some of them are left blank, or null. I want to JOIN these two DataTables using LINQ where the UPC fields are equal. However, I have run into the following error:

Cannot cast DBNull.Value to type 'System.Decimal'. Please use a nullable type

This error occurs when I try to join the two tables because of the null fields.

My LINQ code is as follows:

Dim query = From c In dtDollars.AsEnumerable() _
      Join r In dtUnits.AsEnumerable() _
      On c.Field(Of String)("UPC") Equals r.Field(Of String)("UPC") _
      Select _
      New _
      With {.UPC = r.Field(Of String)("UPC"), .WIC_NUMBER = c.Field(Of String)("WIC_NUMBER"), _
      .WAG_ITEM_DESC = c.Field(Of String)("WAG_ITEM_DESC"), _
      .WAG_BRAND = c.Field(Of String)("WAG_BRAND"), .UOM = c.Field(Of String)("UOM"), _
      .GSK_PROMO_GRP = c.Field(Of String)("GSK_PROMO_GRP"), _
      .TOTAL_DOLLARS = c.Field(Of Decimal)("TOTAL_DOLLARS"), _
      .TOTAL_UNITS = r.Field(Of Integer)("TOTAL_UNITS"), _
      .WKND_DATE = c.Field(Of DateTime)("WKND_DATE")}

Answer 1

Given that WKND_DATE can also be null, get the field as a Nullable(Of DateTime) (DateTime?) like so:

Dim query = From c In dtDollars.AsEnumerable() _
   Join r In dtUnits.AsEnumerable() _
   On c.Field(Of String)("UPC") Equals r.Field(Of String)("UPC") _
   Select _
   New _
   With {.UPC = r.Field(Of String)("UPC"), .WIC_NUMBER = c.Field(Of String)("WIC_NUMBER"), _
   .WAG_ITEM_DESC = c.Field(Of String)("WAG_ITEM_DESC"), _
   .WAG_BRAND = c.Field(Of String)("WAG_BRAND"), .UOM = c.Field(Of String)("UOM"), _
   .GSK_PROMO_GRP = c.Field(Of String)("GSK_PROMO_GRP"), _
   .TOTAL_DOLLARS = c.Field(Of Decimal?)("TOTAL_DOLLARS"), _
   .TOTAL_UNITS = r.Field(Of Integer?)("TOTAL_UNITS"), _
   .WKND_DATE = c.Field(Of DateTime?)("WKND_DATE")}