SAMPLE: ATL2ADO.exe Returns Disconnected ADO Recordset (200122)

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FileName                   Size
---------------------------------------------------------
adostudent.mdb             72
readme.txt                 491
helper.idl                 21
R1ADOdrsExe.aps            4332
R1ADOdrsExe.cpp            4447
R1ADOdrsExe.dsp            12760
R1ADOdrsExe.dsw            545
R1ADOdrsExe.h              84
R1ADOdrsExe.idl            756
R1ADOdrsExe.rc             2941
R1ADOdrsExe.rgs            185
R1ADOdrsExeps.def          253
R1ADOdrsExeps.mk           502
r1DisRS.cpp                473
r1DisRS.h                  891
r1DisRS.rgs                645
resource.h                 549
StdAfx.cpp                 315
StdAfx.h                   1091
				

ATL2ADO.exe is a sample that demonstrates a minimal three-tiered Database Application using ADO 2.0. An ATL server in the middle tier returns a read/write disconnected recordset to a Visual Basic client for presentation. The Visual Basic client can change the data and send it to the server to be updated. The business logic is located in the COM server. The ATL COM server updates the Database tier.

In addition, ATL2ADO.exe demonstrates how to create a simple ATL COM object that returns a disconnected ADO recordset. The sample includes a Visual Basic client that uses the ADO _Recordset returned from the ATL COM Server. The Visual Basic client can change the record data and use the UpdateBat method provided by the server to save changes to the database. After extracting the files, build the Visual C++ project first to register the COM Objects and then use Visual Basic 6.0 to build the client program. The client and server can be distributed to different computers on the network.

The sample also shows how to build the proxy/stub DLL that is used to marshal the recordset. The sample includes an Access .mdb file that you can use with Access and SQL to build the student table that you can use with SQL Server. Use the following query with the GradYear parameter supplied by the Visual Basic client:

"SELECT * FROM Student WHERE GradYear > ?"
				

Build the Visual C++ project with Visual C++ 6.0 to create and register the server and the proxy/stub DLL. Build the Visual Basic project with Visual Basic version 6.0. You can build the server on one computer and the client on another computer on the same network. Copy the included Access database, ADOStudent.mdb, to C:\test (or change the connection string in the source file).

The sample server is created with the ATL COM AppWizard as an .exe server. A simple object ( r1DisRS ) is inserted. You need to make the following additions to the .idl file:

1. Import helper.idl. The file name "helper.idl" is arbitrary. "helper.idl" consists of one line: import msado15.idl. You must import ADO indirectly to successfully build the proxy/stub DLL. Otherwise, MIDL gives you compiler errors.
2. Add the following three methods to the interface:

   getRS([in,optional,defaultvalue(88)] short GY, [out, retval]_Recordset **ppRS);
   ConnString([in] BSTR newVal);
   UpdateBat( _Recordset *ppRS);
   						

You must also create a file helper.h with the following contents:

struct _Recordset;
#if !defined(__cplusplus) || defined(CINTERFACE)
   typedef struct _Recordset _Recordset;
#endif
				

ADO is imported through the file stdAfx.h with the following two lines:

#undef EOF                          // Necessary for EOF collision.
#import "msado15.dll" no_namespace  // Correct place to import ADO.
				

From the Project Settings menu, click Post Build tab, add the "build & Reg Proxy/Stub DLL" as the description, and add the following two commands:

nmake /f R2ADOmodps.mk
regsvr32  R1ADOdrsExeps.dll
				

This allows Visual C++ to automatically build and register the proxy/stub DLL. You must also specify Win32 Debug on the build bar.

The Visual Basic client sets the recordset property MarshalOptions to adMarshalModifiedOnly so that only the modified records are marshaled back to the server. Note that once you click commandSave, the recordset is trimmed to just the modified records. You must click CommandGetRS to retrieve the entire recordset back to the Visual Basic client.

You can build the Visual C++ project on Computer1 and build the Visual Basic client on Computer2. To specify the remote computer (Computer1 in the following example) use the following Visual Basic syntax:

Set idrs = CreateObject("R1ADOdrsExe.r1DisRS", "Computer1")
				

Create Student Table on SQL Server

// Use the following SQL to create the student table on SQL Server.
   CREATE TABLE student
      (studentID int IDENTITY (1000, 1) NOT NULL ,
      name text NULL ,
      gradYear int NULL )
   GO
   INSERT INTO student (name, gradYear)
   VALUES ('Billy Reubin', 99)
   go
   INSERT INTO student (name, gradYear)
   VALUES ('Joe Mana', 98)
   go
   INSERT INTO student (name, gradYear)
   VALUES ('Willy Klifton', 69)
   go

   INSERT INTO student (name, gradYear)
   VALUES ('Lerry ElvisSon', 73)
   go