Execute MySQL stored procedure with parameters in Access frontend via VBA - mysql

Question

So, database hotchpotch.
I have a MySQL database which has stored procedures.
I have an Access document which is linked to the MySQL database (I can survey tables) serving as a frontend (with forms and stuff)
I have successfully created a ODBC Pass Through Query (I think that's what they are called) to call one of the stored procedures from the database. The query in Access actually is just CALL myProcName; and gives me the results I expect when I call it from VBA with Set Result = CurrentDb.OpenRecordset("myProcName")
What I am trying to achieve is the following:
Have a stored procedure in MySQL that takes one parameter => check!
Have that stored procedure working as expected => checked in phpMyAdmin => check!
Have a saved query in Access which links to this parametric stored procedure with a fixed parameter value given => check! (CALL myProcName('myParameterValue'), I can call that from VBA just as I do the unparametric query)
Have the ability to specify 'myParameterValue' everytime I execute the query => not check
I need to somehow specify a parameter placeholder in the SQL definition of the saved query and set that parameter in VBA. For the VBA part I have and idea I would find rather elegant:
Private Sub ParametricQuery()
Dim QDef As QueryDef
Set QDef = CurrentDb.QueryDefs("myProcName")
QDef.Parameters(*insert parameter name here*) = parameter value
Dim Result As Recordset
Set Result = QDef.OpenRecordset
Do While Not Result.EOF
MsgBox Result.Fields(1) 'Display a field from the results
Loop
End Sub
But how would I build my SQL definition?
PARAMETERS in_param TEXT;
CALL myProcName(in_param);
does NOT work. If I try
Set QDef = CurrentDb.QueryDefs("myProcName")
MsgBox QDef.Parameters.Count
I get a Messagebox telling me there is a total of 0 parameters in my query definition, so that doesn't work.
What I have found online is a lot of people building the actual SQL in VBA via string operations. That makes me shudder for so many reasons (security, maintainability and elegance among them). I firmly believe that there is a better way, hopefully along the lines I have sketched above. The only problem is: How to do it?

Answer 1

Consider using ADO for a parameterized query to call your stored procedure. Currently, you are using DAO (Access' default database API) to access a pass-thru query (a saved Access querydef). However, this type of query does not see anything in the frontend, only the backend RDMS particularly the MySQL SQL dialect and its connected database objects. Hence, you cannot bind local parameter values to it. And PARAMETERS clause is only part of the Access SQL dialect and will fail MySQL syntax.
MySQL Stored Procedure
CREATE PROCEDURE `mystoredproc`(IN param VARCHAR(254))
BEGIN
SELECT * FROM table WHERE field=param;
END
ADO Parameterized Query
Public Sub CallMySQLProc()
Dim conn As Object, cmd As Object, rst As Object
Const adCmdStoredProc = 4, adParamInput = 1, adVarChar = 200
Set conn = CreateObject("ADODB.Connection")
Set rst = CreateObject("ADODB.Recordset")
' DSN-LESS CONNECTION
conn.Open "Driver={MySQL ODBC 5.3 Unicode Driver};host=hostname;database=databasename;" _
& "UID=username;PWD=****"
' CONFIGURE ADO COMMAND
Set cmd = CreateObject("ADODB.Command")
With cmd
.ActiveConnection = conn
.CommandText = "mystoredproc"
.CommandType = adCmdStoredProc
.CommandTimeout = 15
End With
' APPEND NAMED PARAM
cmd.Parameters.Append cmd.CreateParameter("param", adVarChar, _
adParamInput, 254, "some.name#example.com")
Set rst = cmd.Execute
' FREE RESOURCES
rst.Close
Set rst = Nothing
Set cmd = Nothing
Set conn = Nothing
End Sub
DAO Dynamic Pass-Through Query
Here, you can build the querydef's .SQL statement dynamically, but will not be parameterized:
Private Sub ParametricQuery()
Dim QDef As QueryDef
Dim Result As Recordset
Set QDef = CurrentDb.QueryDefs("PassThruQ")
QDef.SQL = "CALL mystoredproc('some.name#example.com')"
Set Result = QDef.OpenRecordset
Do While Not Result.EOF
Debug.Print Result.Fields(1) 'Print to immediate window a field from the results
Loop
Result.close
Set Result = Nothing
Set QDef = Nothing
End Sub