Implicit conversion from object to integer and other errors - sql

Question

I have two Layes Classes Business Layer And Data Layer And i have The Main class i called DatabaseManager contain all functions i need for stored procedures
I search on these errors I cannot find solutions
First Error in DatabaseManager class is :
implicit conversion from object to integer
Public Function ExecuteScalar(ByVal sql As String) As Object
Dim cmd As New SqlCommand(sql) With {
.CommandType = CommandType.Text,
.Connection = Connection
}
Dim retval As Integer = ExecuteScalar(cmd)
Return retval
End Function
In Data Layer Class i have this code :
Friend Function Get_Last_Visits_Type(ByRef cmd As SqlCommand)
Dim retval As Integer
cmd = New SqlCommand("Get_Last_Visits_Type")
retval = dm.ExecuteScalar(cmd)
Return retval
End Function
I got two errors here
function without an 'as' clause return type of object assumed
And
implicit conversion from object to integer
When Form Loaded i put this code on Load action :
TxtVisitTypeID.Text = Val(p.Get_Last_Visits_Type)
And i got this error :
implicit conversion from Double to String
Thanks...

Answer 1

Quite a few problems here as mentioned in comments:
Avoid naming a function anything that is a reserved word in the scope of your project at the very least: ExecuteScalar is a method of SqlCommand so use something like MyExecuteScalar instead.
Dim retval As Integer = ExecuteScalar(cmd) probably should be Dim retval As Integer = cmd.ExecuteScalar() unless you want a recursion (which I doubt). (Refer 1.)
Turn Option Strict on in your project settings. As mentioned, ALWAYS have this on. (And I prefer to have Option Explicit on and Option Infer off as well for similar reasons.)
With compile options set as in 3. you will have (valid) compilation errors pertaining to type conversion (at least), with a good chance of resulting in working code once you fix them. Eg Dim retval As Integer = Ctype(cmd.ExecuteScalar(), Integer) (if you're sure that the result of the query will be Integer, otherwise you will need to test and/or error trap).
Connection isn't defined anywhere: .Connection = Connection. You don't pass it nor declare it.
Since retval is declared as an Integer then the return type can also be tightened up to Integer as well, rather than Object.
Your second function has no return type.
What is dm? Not declared/defined.
Consider using Using blocks to close-and-dispose of SQL connection and command on exit.
CommandType.Text is the default so you only need to state it by way of explanation.
Here's what I'd do with your first function:
Public Function MyExecuteScalar(ByVal sql As String) As Integer
Try
Using con As New SqlConnection(sql)
Using cmd As New SqlCommand(sql, con)
Return CType(cmd.ExecuteScalar(), Integer)
End Using
End Using
Catch
Return -1 ' Or something recognizable as invalid, or simply Throw
End Try
End Function

Answer 2

Addressing the first function:
This code is too abstract to be useful. The name of the function is bad. It appears to be recursive but the value you pass back to the function is not a string but a command. If the line of code is Dim retval As Integer = cmd.ExecuteScalar(), then .ExecuteScalar() returns an Object. You cannot convert an Object to an Integer without a conversion method. If you are declaring retval as an Integer why would you have typed your function As Object? I won't even get into the connection problem here. I suggest you delete the function and start again.
Addressing the second function:
Why are you passing the command ByRef? This function has no connection at all! How do you expect it to execute anything? Same problem with retval As Integer and ExecuteScalar returning an Object.
Again, delete and start again.
Now to the code in Form.Load:
Val went out with VB6. I can give unanticipated results. Guess what, Val returns a Double. A .Text property expects a string. Also you appear to be calling the function you showed us above. That function asks for the calling code to provide an argument, namely an SqlCommand object.
My suggestions:
Forget about layers and try to learn the basics of data access with ADO.net. Turn on Option Strict now and forever. Ask new questions with a single problem. Tell us what line the error occurs on. You have been advised before that functions require a datatype but it doesn't seem to sink in.