How do I generate a new Primary Key ID through code? - mysql

Question

So basically I'm trying to write the below code to the database and I have the primary key as an Int and it was autogen but when writing to the database it didnt allow me to do it kept telling me that I wasn't allowed to enter a null value (because the code is obviously not writing to the primary key field) so I used the line
cmd.Parameters.Add("#EventID", SqlDbType.Int).Value = 3
But the problem is I have to change the value each time I want to test a new record i.e. 1,2,3,4 and so on. I was wondering is there a line of code I can put in to make it create a value by adding +1 each time so I don't need to go into the code and enter a new number each time. Below is the full code writing to the database so you can see a better view of it
Dim Con As SqlConnection
Dim cmd As SqlCommand
Dim recordsAffected As String
Dim cmdstring As String = "INSERT [Event Table](EventID, EventTypeID, EventName, VenueName, NumberOfGuests, Date, ClientAddress, WeddingName, BuildingAddress) Values(#EventID, #EventTypeID, #EventName, #VenueName, #NumberOfGuests, #Date, #ClientAddress, #WeddingName, #BuildingAddress)"
Con = New SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\YellowDoor.mdf;Integrated Security=True;User Instance=True")
cmd = New SqlCommand(cmdstring, Con)
cmd.Parameters.Add("#EventID", SqlDbType.Int).Value = 3
cmd.Parameters.Add("#EventTypeID", SqlDbType.Text).Value = EventTypeDD.SelectedValue
cmd.Parameters.Add("#EventName", SqlDbType.Text).Value = EventNametxt.Text
cmd.Parameters.Add("#VenueName", SqlDbType.Text).Value = VenueLoDD.SelectedValue
cmd.Parameters.Add("#NumberOfGuests", SqlDbType.Int).Value = CInt(NumOfGtxt.Text)
cmd.Parameters.Add("#Date", SqlDbType.Int).Value = CInt(DateTxt.Text)
cmd.Parameters.Add("#ClientAddress", SqlDbType.Text).Value = txtAddress.Text
cmd.Parameters.Add("#WeddingName", SqlDbType.Text).Value = txtWedding.Text
cmd.Parameters.Add("#BuildingAddress", SqlDbType.Text).Value = txtBAddress.Text
Con.Open()
recordsAffected = cmd.ExecuteNonQuery
Con.Close()

Answer 1

If your EventID is an IDENTITY column, you should never try to set a value for it.
Just ignore that field both as parameter or inside the INSERT command.
And you can retrieve the value assigned by the database engine to your field in this way
Dim Con As SqlConnection
Dim cmd As SqlCommand
Dim cmdstring As String = "INSERT [Event Table] " & _
"(EventTypeID, EventName, VenueName, NumberOfGuests, [Date], ClientAddress, " & _
"WeddingName, BuildingAddress) Values(#EventTypeID, #EventName, #VenueName, " & _
"#NumberOfGuests, #Date, #ClientAddress, #WeddingName, #BuildingAddress); " & _
"SELECT SCOPE_IDENTITY()"
Using Con = New SqlConnection(".....")
Using cmd = New SqlCommand(cmdstring, Con)
cmd.Parameters.Add("#EventTypeID", SqlDbType.Text).Value = EventTypeDD.SelectedValue
.....
Con.Open()
Dim result = cmd.ExecuteScalar()
if result IsNot Nothing Then
Dim newEventID = Convert.ToInt32(result)
....
End If
End Using
End Using
With this code you don't pass anything for the EventID field but you add a second command text to your query. This second command will return the last value generated for an IDENTITY column by the database for your connection. This double command (A.K.A. batch commands) is executed using ExecuteScalar because we are interested in the single value returned by the SELECT SCOPE_IDENTIY()
Notice also that DATE is a reserved word in T-SQL so it is possible to use it as name of a column only if you enclose it in square brackets