Cannot set Parameter size when using adLongVarChar in MS Access - vba

Question

I have a function that makes a call to a SQL Server database to return a String value. Previously, expected string values were fairly short, but as the character length can exceed 255 on occasion, I have changed the SQL field type in the table to nvarchar(MAX).
In the project, I have altered the code to use adLongVarChar instead of adVarChar and need to specify the length. As there is no length, I know for Input parameters, -1 is the correct length to use. However, when using this as an Output parameter, I receive Run-Time Error 3708 - 'Parameter object is improperly defined. Inconsistent or incomplete information was provided.'
What is the correct syntax to construct the paramter?
Code below:
Public Function getStatus() As String
Dim db As ADODB.Connection
Dim rs As ADODB.Recordset
Dim sp As ADODB.Command
Dim rp1 As ADODB.Parameter
Dim rp2 As ADODB.Parameter
'// Data declarations
Set db = New ADODB.Connection
Set rs = New ADODB.Recordset
Set sp = New ADODB.Command
Set rp1 = sp.CreateParameter("#ksActive", adBoolean, adParamOutput)
Set rp2 = sp.CreateParameter("#ksMsg", adLongVarChar, adParamOutput, -1)
'// Data connection initialisation
db.Open dbString
With sp
.ActiveConnection = db
.CommandText = "dbo.TestProcedureName"
.CommandType = adCmdStoredProc
.Parameters.Append rp1 '// This works fine
.Parameters.Append rp2 '// Error occurs here
.Execute
End With
getStatus = rp2.Value
End Function

Answer 1

TL/DR: Use .Parameters.Refresh and .NamedParameters = True to define output (return) parameters in MS Access ADODB.
I just came across this and had this same problem. I found a hint on MSDN "What is the ADO DataType for nVarchAR(max)". For whatever reason, you MUST include an initial value with the length (at least in Access VBA) for long value parameters in Access ADO. I found adding NULL works just fine to satisfy it, especially when you set the values later for stored commands.
NOTE: This will only work for input values (as shown here, outputs cannot be defined like this)
' Note: only works for output params.
Set rp2 = sp.CreateParameter("#ksMsg", adLongVarChar, adParamInput, -1, NULL)
Output Parameter definition:
Using OP's names:
Public Function getStatus() As String
Dim db As ADODB.Connection
Dim rs As ADODB.Recordset
Dim sp As ADODB.Command
Dim rp1 As ADODB.Parameter
Dim rp2 As ADODB.Parameter
'// Data declarations
Set db = New ADODB.Connection
Set rs = New ADODB.Recordset
Set sp = New ADODB.Command
'// Data connection initialisation
db.Open dbString
Dim sp As ADODB.Command
With sp
.ActiveConnection = db
.CommandText = "dbo.TestProcedureName"
.CommandType = adCmdStoredProc
.Parameters.Refresh
.NamedParameters = True
Set rp1 = .Parameters("#ksActive")
Set rp2 = .Parameters("#ksMsg")
' Set outputs to null because they're cached, and if your
' second call returns nothing, you'll get the prior call's results.
rp1.Value = Null
rp2.Value = Null
.Execute
End With
getStatus = rp2.Value
End Function
You need to use sp.Parameters.Refresh to define output parameters for stored procedures. After scouring the internet, it appears that there's an issue with using MS Access ADODB adLongVarWChar (or any long / wide return variable) and adParamOutput or adParamInputOutput and defining them explicitly.
I have found the only way to get Output Parameters to work is to use .Parameters.Refresh; once I did that, it works just fine (and returns correctly).
Just be sure to clear them out before executing (set outputs to null) or you'll get the previously cached result back (and it will send you on a wild goose chase).