Cannot add an entity that already exists. (LINQ to SQL)

Question

Hello guys, in my database there are 3 tables

CustomerType
CusID

EventType
EventTypeID

CustomerEventType
CusID
EventTypeID

Dim db = new CustomerEventDataContext
Dim newEvent = new EventType
newEvent.EventTypeID = txtEventID.text
db.EventType.InsertOnSubmit(newEvent)
db.SubmitChanges()

'To select the last ID of event'
Dim lastEventID = (from e in db.EventType Select e.EventTypeID Order By EventTypeID Descending).first()

Dim chkbx As CheckBoxList = CType(form1.FindControl("CheckBoxList1"), CheckBoxList)
Dim newCustomerEventType = New CustomerEventType
Dim i As Integer
For i = 0 To chkbx.Items.Count - 1 Step i + 1
    If (chkbx.Items(i).Selected) Then
        newCustomerEventType.INTEVENTTYPEID = lastEventID
        newCustomerEventType.INTSTUDENTTYPEID = chkbxStudentType.Items(i).Value
        db.CustomerEventType.InsertOnSubmit(newCustomerEventType)
        db.SubmitChanges()
    End If
Next

It works fine when I checked only 1 Single ID of CustomerEventType from CheckBoxList1. It inserts data into EventType with ID 1 and CustomerEventType ID 1. However, when I checked both of them, the error message said

Cannot add an entity that already exists.

Any suggestions please? Thx in advance.

Answer 1

Did you change the EventID before you pressed the button again. To me it looks as you did not. This would result that the code tries to insert the event with the ID 1 into the database, although, it is already there.

Maybe try increasing the event ID automatically or check whether the event is alreay present before trying to insert it.

Edit:

OK, here is what I think you want to do ... if I understood it correctly (it's in C# as I am more fluent in that language - however you should be able to easily convert the algorithm to VB - so just take it as pseudo code):

var db = new CustomerEventDataContext();
var newEvent = db.EventTypeSingleOrDefault(x => x.EventTypeId == txtEventID.Text);
if (newEvent != null) {
    newEvent = new EventType();
    newEvent.EventTypeId = txtEventID.Text;
    db.EventType.InsertOnSubmit();
}

var chkbx = (CheckBoxList) form1.FindControl("CheckBoxList1");
for (int i = 0; i < chkbx.Items.Count; i++) {
    var value = chkbxStudentType.Items(i).Value;
    if (db.CustomerEventTypes.SingleOrDefault(x => x.EventTypeId == newEvent.EventTypeId) != null) {
        // item already exists
    } else {
      var newCustomerEventType = new CustomerEventType();
      newCustomerEventType.INTEVENTTYPEID = newEvent.EventTypeId;
    newCustomerEventType.INTSTUDENTTYPEID = value;
    db.CustomerEventType.InsertOnSubmit(newCustomerEventType);
    }
}

db.SubmitChanges();

Two things I noticed:

1. You were adding the new EventType and then selecting the last event type based upon the id. This may not result in the item you just added.
2. You do not have to call SubmitChanges after each InsertOnSubmit. The DataBaseContext implementaton holds the inserted objects for you and you can reference them. Then you do a single submit to commit all changes. Note, however, in some complex circumstances a separate SubmitChanges is necessary, but this is rarely the case.