主题：跨表引用时为何出现如下提示？

当进行跨表引用时为何出现如下提示

Exception has been thrown by the target of an invocation.

Conversion from string "产品名称='PSD1'" to type 'Long' is not valid.

Input string was not in a correct format.

Select Case e.DataCol.name

Case "产品名称","型号","规格"

Dim dr As DataRow = e.DataRow

Dim pr As DataRow

If dr.Isnull("产品名称") OrElse dr.Isnull("型号") OrElse dr.Isnull("规格") Then

dr("产品单价") = Nothing

Else

Dim filter As String

filter = "产品名称='" &dr("产品名称") &"'" And"型号='" &dr("型号") &"'" and"规格='" &dr("规格") &"'" 

pr =DataTables("产品表").find(filter)

If pr IsNot Nothing Then

dr("产品单价") = pr("产品单价")

End If

End If

End Select