Null reference exception in Transaction

Im having problem with a null reference exception while executing the code

trans.Rollback() . Kindly help ASAP.

Thanx in Advance.

FYI:

Dim trans As OleDbTransaction
Try
trans = con.BeginTransaction
If con.State = ConnectionState.Closed Then
con.Open()
End If
Dim cmd_inward As OleDbCommand = New OleDbCommand("Insert into inward_entry(in_date,product_name,batch_no,Pack,type, qty,Description,Mfd_Company,Exp_Date,Purchased_price,MRP) values (#" & Todate & "#,'" & Prd_nm & "', '" & Prd_batch & "','" & Prd_pack & "', '" & prd_type & "','" & item_Qty & "', '" & prd_description & "','" & Mfd_By & "','" & exp_dt & "', '" & Pur_prc & "','" & Prd_MRP & "')", con)
cmd_inward.Transaction = trans
cmd_inward.ExecuteNonQuery()
Dim cmd_pur_mast As OleDbCommand = New OleDbCommand("insert into purchase_master (purchase_date,product_name,item_pack,Batch_no,product_purchase_price,item_qty) values (#" & Todate & "#, '" & Prd_nm & "','" & Prd_pack & "','" & Prd_batch & "', '" & Pur_prc & "','" & item_Qty & "')", con)
cmd_pur_mast.Transaction = trans
cmd_pur_mast.ExecuteNonQuery()
Dim cmd_prd_mast As OleDbCommand = New OleDbCommand("insert into product_master(product_name, item_pack,product_manufacturer,product_description) values ('" & Prd_nm & "','" & Prd_pack & "','" & Mfd_By & "','" & prd_description & "')", con)
cmd_prd_mast.Transaction = trans
cmd_prd_mast.ExecuteNonQuery()
Dim cmd_select_warehouse As OleDbCommand = New OleDbCommand("Select * from warehouse_master where product_batch_no='" & Prd_batch & "' and product_name='" & Prd_nm & "' and item_pack='" & Prd_pack & "' ", con)
Dim rdr As OleDbDataReader
rdr = cmd_select_warehouse.ExecuteReader()
If rdr.Read() = False Then
Dim cmd_insert As OleDbCommand = New OleDbCommand("Insert into warehouse_master(product_batch_no, product_manufacturer, product_name,item_pack, available_qty,product_exp_date,product_MRP) values('" & Prd_batch & "','" & Mfd_By & "','" & Prd_nm & "', '" & Prd_pack & "','" & item_Qty & "', '" & exp_dt & "', '" & Prd_MRP & "')", con)
cmd_insert.Transaction = trans
cmd_insert.ExecuteNonQuery()
Else
MessageBox.Show("data")
Dim cmd_update As OleDbCommand = New OleDbCommand("Update warehouse_master set available_qty= available_qty + '" & item_Qty & "' where product_batch_no = '" & Prd_batch & "' and product_Name = '" & Prd_nm & "' and Item_pack= '" & Prd_pack & "'", con)
cmd_update.Transaction = trans
cmd_update.ExecuteNonQuery()
End If
trans.Commit()
Catch ex As Exception
trans.Rollback()
MessageBox.Show("Transaction Rolled Back")
Finally
con.Close()
End Try

7 Replies

Know the answer? Post it — somebody with the same question will find it here.

knights15y ago
Hi,
The object trans is declared and initilized in Try block and that is why without being assinged any value, it will give Null reference exception.
Since you are using VB.Net it must have given you a warning at compilation. I am suggesting the following modification.Thanks
trans = con.BeginTransaction
If con.State = ConnectionState.Closed Then
     con.Open()
End If
trans = con.BeginTransaction
Try ......
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Suthish Nair15y ago
the link posted have full code, might that helps him
0
Sam Hobbs15y ago
Suthish, Gyanaranjan says that the error is occurring in the call to trans.Rollback() and that call is in the Catch block. Since this is VB my mind does not work so well.

Probably the problem is that the BeginTransaction is before the connection is opened.
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Suthish Nair15y ago
no no.. i not saying to remove try-catch.. sorry..
Compare both codes how the transaction got created and used.
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Sam Hobbs15y ago
Suthish, that sample code does not use try/catch; are you suggesting removal of try/catch? If so then I disagree with that solution. If not then how is the sample relevant?
0
Suthish Nair15y ago
Follow this link and check what you missing in code.
0
Sam Hobbs15y ago
Nearly always a null reference exception is the result of something that does not exist; in your situation, trans does not exist in the Catch block; trans is created in the try block.
0