while saving data from grid view getting object reference error in windows forms

Question

i am working on vb.net windows form application ,,i have a data grid

enter image description here

I have two tables 1->CompanyMaster_tbl in this having Two fields . Cid and CompanyName,

Cid is the primary key of this table

2->DepartmentMaster_tbl in this having 4 fields. dtid,dtname,dtphon,dtmail,Cid.

dtid is the primary key,and Cid is the foreign key

while clicking save button i want save the data in both table. in one company i want to save multiple departments. my Cid and dtid are autoincriment,,i mean Identity specication i set as true..in save button i given code like this,,

 Dim sqlInsertT1 As String = ""
 Dim sqlInsertT2 As String = ""
 Dim CompanyMaster_tbl As DataTable = Nothing
 Dim DepartmentMaster_tbl As DataTable = Nothing

 For Each CompanyMaster_row As DataRow In CompanyMaster_tbl.Rows
   For i As Integer = 0 To gv.RowCount - 2
     If gv.Rows(i).Cells("cmpny").Value <> "" Then
       sqlInsertT1 &= "Insert Into CompanyMaster_tbl(CompanyName) Values ('" & gv.Rows(i).Cells("cmpny").Value & "');"
       Exetransaction(sqlInsertT1)
     End If
     Ccid = RecordID("Cid", "CompanyMaster_tbl", "CompanyName", gv.Rows(i).Cells("cmpny").Value)
   Next

   For Each DepartmentMaster_row As DataRow In DepartmentMaster_tbl.Select(Ccid)
     For j As Integer = 0 To gv.RowCount - 2
       sqlInsertT2 &= "Insert Into DepartmentMaster_tbl(dtname,dtphone,dtEmail,Cid) Values ('" & gv.Rows(j).Cells("Dpmnt").Value & "','" & gv.Rows(j).Cells("dtphon").Value & "','" & gv.Rows(j).Cells("mail").Value & "'," & Ccid & ");"
       Exetransaction(sqlInsertT2)
     Next
   Next
 Next

but this logic is not enough for saving this data,,
in save button if i am editing something in grid view ,,i want to update that value in particular table
in the below line i am getting error like this:Object reference not set to an instance of an object.

For Each CompanyMaster_row As DataRow In CompanyMaster_tbl.Rows

so how i can resolve this issue? i try after filling my company master table,,but then also i am getting same error

Initially i would suggest you to use transaction. After insert you can select scope_identity in order to get the just inserted id. — kostas ch.
– kostas ch., Commented Dec 31, 2013 at 13:46
What's the relationship between the datatables and the datagridview? Are they bound? If not, how is the datagridview populated? — stuartd
– stuartd, Commented Dec 31, 2013 at 13:57
in load event i written some coding for populating the data grid view,, — user3106114
– user3106114, Commented Dec 31, 2013 at 14:05
i am taking each value then i am passing to datagridview, like this: Dim row0 As String() = {cmpname, dtname, dtphon, dtmail} gv.Rows.Add(row0) — user3106114
– user3106114, Commented Dec 31, 2013 at 14:07

stuartd · Accepted Answer · 2013-12-31 13:53:07Z

2

In your posted code, you have assigned a value of Nothing to CompanyMaster_tbl just before you try to access it. That's why you're getting the exception.

Dim CompanyMaster_tbl As DataTable = Nothing

For Each CompanyMaster_row As DataRow In CompanyMaster_tbl.Rows

The exception is thrown when you try to access the Rows property of the null object.

edited Dec 31, 2013 at 13:53

answered Dec 31, 2013 at 13:47

stuartd

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3 Comments

user3106114 Over a year ago

instead of nothing i given my table name ..then also i am getting error

Ňɏssa Pøngjǣrdenlarp Over a year ago

fill/get/populate CompanyMaster_tbl before you try to iterate it

user3106114 Over a year ago

i filled CompanyMaster_tbl manually,,then i try to iterate ..but getting same error

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