Part One, The Win32 DLL Object

First, we are going to make the Win32 DLL core files for the project, W32DLL.xxx.

1. Start Visual C++ Studio.
2. Close any open workspace and all files.
3. Select New from the file menu.
4. Select Project: Win32 Dynamic-Link Library.
5. Give the the project a fitting name, say, W32DLL, make sure the location is acceptable and click OK.
6. Select the "A simple DLL project" radio button.
7. Click Finish and OK.

Next, we are going to make the DLL declaration/header file: DLLCode.h. Select New from the file menu, then select "C/C++ Header File" and name the file DLLCode. Click OK.

Copy and paste the following code excerpt:

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/*******************************************************
   File name: DLLCode.h

   This file contains all the DLL interfacing object 
   declarations, in this example:
   a class object, two global function object, and 
   a global integer variable. 
   Notice: we use the same header file for compiling the 
   .DLL and the .exe (application).
   This header file defines a macro which export the target 
   DLL objects if we are building
   a DLL, otherwise it import the DLL objects into an 
   application which uses the DLL. If
   we define DLLDIR_EX (a preprocessor identifier), 
   then the preprocessor define macro
   DLLDIR (a mnemonic for DLL import/export Direction) 
   becomes an export instruction,
   otherwise its an import instruction by default. 
************************************************************/ 
#ifdef DLLDIR_EX
   #define DLLDIR  __declspec(dllexport)   // export DLL information
#else
   #define DLLDIR  __declspec(dllimport)   // import DLL information
#endif 

// The extern "C" declaration allows mixed languages compactability,
// it prevents the C++ compiler from using decorated (modified)
// names for the functions 
extern "C" { 
       void DLLDIR DLLfun1(char*);
       int  DLLDIR DLLfun2(int);
}; 
extern int  DLLDIR DLLArg; 

class DLLDIR DLLclass
{
   public:
      DLLclass();          // Class Constructor
      ~DLLclass();         // Class destructor
      int Add(int, int);   // Class function Add
      int Sub(int, int);   // Class function Subtract
      int Arg;             // Warning: you should not 
               // import class variables
               // since the DLL object can be dynamically unloaded.
};

Save and close this header file. Now we are going to create the DLL implementation file, DLLCode.cpp.

Select New from the file menu, then select "C++ Source File" and name the file DLLCode. Then click OK.

Copy and paste the following code excerpt:

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/*********************************************************
   File name: DLLCode.cpp 

   The header file, DLLCode.h, prototypes 
   all of the DLL interface objects 
**********************************************************/
#include "Stdafx.h"
#include "DLLCode.h"
#include <iostream> 

using namespace std; 

void DLLfun1(char* a)
{
   cout << a << endl;
}; 

int DLLfun2(int a) { return a<<1; }; 

int DLLArg = 100; 

DLLclass::DLLclass() {}; 
DLLclass::~DLLclass() {}; 

int DLLclass::Add(int a, int b)
{
   return a + b;
}; 

int DLLclass::Sub(int a, int b)
{
   return a - b;
};

We want to access the DLL, so we need to export it. When the DLL is built, it also builds something called an export library. The export library is similar to a regular library. It contains all of the information necessary to dynamically link to the DLL at runtime. When we export a function or a class, the function name and location is stored in the export library. The application uses the DLL links in the export library to access the DLL.

To create the DLL export library, select "setting..." from the Project menu. Select the C/C++ tab. Append, or insert, ",DLLDIR_EX" (without the quotation marks) to the Preprocessor Definition text box. Then click OK. This will prevent compiler assumptions and warnings.

Note, Visual C++ defines an export macro <projectname>_EXPORTS, in our case, W32DLL_EXPORTS. But we used DLLDIR_EX, a generic macro name.

Click the "!" button to compile, build, and run the W32DLL project.

Close the "Executable For Debug Session" dialog box, we ran the DLL prematurely.

Congratulation, you finished building the Win32 DLL and its export Library.

Part Two, DLL Client Application One

This is the simplest and most versatile DLL Client, without MFC. This flexibility is due to the DLL export library information.

Now, we are going to make a Win32 console application, project DLLClient1. In this application, the DLL is loaded at application startup, "Load Time" linkage.

1. Close any open workspace and files, then select New from the File menu.
2. Select Win32 Console Application.
3. In the Project name box, give the project a fitting name, say, DLLClient1, then click Next.
4. Select "An empty project", then click Finish and OK.

Next, we are going to make the C/C++ source file: DLLClient1. Select New from the File menu, then select "C/C++ Source File". In the File Name box, give it a fitting name, say, DLLClient1, then press the Enter key.

Copy and paste the following code excerpt:

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/***********************************************************
   File name: DLLClient1.cpp
***********************************************************/ 
#include <iostream>
#include <conio.h>
#include <windows.h>
#include "DLLCode.h"
#pragma comment(lib,"W32DLL.lib") 

using namespace std; 

int main()
{
   int a, b, c;
   DLLclass classFromDLL; 
   classFromDLL.Arg = 6; 
   a = classFromDLL.Add(3, 2);
   b = classFromDLL.Sub(3, 2);
   c = classFromDLL.Arg;
  
   cout << "DLL class Add function return: " << a << endl;
   cout << "DLL class Sub function return: " << b << endl;
   cout << "DLL class Arg Variable return: " << c << endl; 
   getch();

   a = DLLArg;
   b = DLLfun2(30);

   DLLfun1("this is the string pass to function DLLfun1");

   cout << "\n\nDLL Variable DLLArg return: " << a << endl;
   cout << "DLL function DLLfun2 return: " << b << endl; 
   getch();
 
   return 0;
}

Save and close this C++ source file, then minimize the VC++ Studio window. We must get some common files from the W32DLL project. So, Copy, don't move, the following files to the DLLClient1 project directory:

• W32DLL\Debug\W32DLL.DLL
• W32DLL\Debug\W32DLL.lib
• W32DLL\DLLCode.h

If you don't see the .DLL file in the Debug or Release folders, then select the View, or Tool (depending on the operating system) menu option, then select Folder Options. Next click on the View tab. Select option: Show all files. Then re-examine the Debug or Release folder.

Now maximize the VC++ Studio window, then click the "!" button to compile, build, and run the application.

If you have a DLL you use in many projects, then you can take advantage of the VC++ file architecture. Copy the DLL file into the system directory and the LIB file into the Visual C++ Lib directory. See Options on the Tools menu, and select the Directories tab, there are search directories for EXEs, SOURCE CODEs, and LIBs.

In this part, the DLL is loaded at application startup time. The Operating System searches the DLL in the following locations:

• The Windows System directory
• The Windows directory
• The Application local path
• The directories listed in the environment path variable

For simplicity, we just copy the common files to the target directory, DLLClient1.

Part Three, DLL Client Application Two

This DLL Client is for DLLs which do not have an export library, hints, we can't import the DLL header file. Note, we are restricted to function calls.

Now, we are going to make a Win32 console application, project DLLClient2.

In this application, the DLL is loaded during execution of the application, "Run Time" DLL linkage.

1. Close any open workspace and files, then select New from the File menu.
2. Select Win32 Console Application.
3. In the Project Name box, give the project a fitting name, say, DLLClient2, then click Next.
4. Select "An empty project", then click Finish and OK.

Next, we are going to make the C/C++ source file DLLClient2.

Select New from the File menu, then select "C/C++ Source File". In the File Name box, give it a fitting name, say, DLLClient2, then press the Enter key.

Copy and paste the following code excerpt:

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/************************************************************
   File name: DLLClient2.cpp
************************************************************/ 
#include <conio.h>     // Header file containing getch() prototype
#include <iostream>
#include <windows.h> 

using namespace std; 

typedef void (*MYFUN1)(char*);  // pointer to: void function(char*)
typedef int  (*MYFUN2)(int);    // pointer to: int  function(int) 
int main()
{

  MYFUN1  pfun1;              
  MYFUN2  pfun2;              
  HMODULE hMod;        // handle to loaded library module
  BOOL    bRes;        // BOOL to check if DLL was successfully unloaded 

  // returns a handle to the DLL, otherwise NULL
  hMod = LoadLibrary("W32DLL.DLL");
 
  // returns the address of the DLL functions, otherwise NULL
  pfun1 = (MYFUN1) GetProcAddress(hMod, "DLLfun1");
  pfun2 = (MYFUN2) GetProcAddress(hMod, "DLLfun2");
 
  // (DLL function address) (function parameters)
  (pfun1)("this is the string pass to function DLLfun1");
 
  // (DLL function address) (function parameters)
  int a = (pfun2) (30);
 
  cout << "DLL function DLLfun2 return: " << a << endl;
  cout << "Press a key to exit" << endl;
  getch();
 
  ///////////////////////////////////////////////////////
  // This code will run if you compile the W32DLL project
  // with the W32DLL.def file to explicitly export DLLArg.
  int *i;
  i = (int*) GetProcAddress(hMod, "DLLArg");

  if (i)
  {
   cout << "Variable DLLArg is: " << *i << endl;
  };

  cout << "Press a key to exit" << endl;
  getch();

  // returns nonzero if sucussful 
  bRes = FreeLibrary(hMod); 
  return 0;
}
// ===========  Code snippet 4  ====================

Save and close this C++ source file, then minimize the VC++ studio window. Copy, don't move, the following file to the DLLClient2 project directory:

W32DLL\Debug\W32DLL.DLL

Now maximize the VC++ Studio window, then click the "!" button to compile, build, and run the application.

In this part, the DLL is loaded at application run time. The LoadLibrary function is used to load a DLL at run time. Being that we dynamically loaded the library, we should free this resource when we are finished with it.

Addendum

This subsection was added as a result to user Hing's comment.

The code in "Code snippet 4" was modified to add code for accessing the global variable DLLArg. Note, in the application you just ran, DLLCient2, function call GetProcAddress(hMod, "DLLArg") returned a NULL pointer. To add the global variable name to the DLL object, you must add a new text file to the W32DLL project. Go to New on the File menu. Select "Text File" on the File tag. Name the file: "W32DLL.def", the "def" file extension is important. Click OK.

Add the following text:

;File: W32DLL.def (explicitly export the global object names.)
LIBRARY W32DLL.dll
EXPORTS
   DLLfun1
   DLLfun2 
   DLLArg

Save and recompile the W32DLL project. Copy the new W32DLL.DLL file to the project DLLClient2 directory. Run the DLLClient2 application.

Function GetProcAddress should find variable "DLLArg".

Note: You CANNOT export a class object to the DLL. The library object contains that information, along with the header file.

Part Four, MFC DLL Object

This time, we are going to make the MFC DLL core files for the project, RMFCDLL.xxx.

1. Start Visual C++ Studio.
2. Close any open workspace and all files.
3. Select New from the File menu.
4. Select Project: MFC AppWizard(DLL).
5. Give the the project a fitting name, say, RDLLMFC, make sure the location is acceptable and click OK.
6. Select the "Regular DLL using shared MFC DLL" radio button.
7. Click Finish and OK.

Next, we are going to make the DLL declaration header file: DLLCode.h. Select New from the File menu, then select "C/C++ Header File" and name the file DLLCode. Click OK.

Copy and paste the following code excerpt:

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/******************************************************
   File name: DLLCode.h 

   This file contains MFC objects, hints, 
   you should use a MFC Client. 
   Notice: we use the same header file for compiling 
   the .DLL and the .exe (application).
   This header file defines a macro which export the
   target DLL objects if we are building
   a DLL, otherwise it import the DLL objects into an
   application which uses the DLL. If
   we define DLLDIR_EX (a preprocessor identifier), 
   then the preprocessor define macro
   DLLDIR (a mnemonic for: DLL import/export Direction)
   becomes an export instruction,
   otherwise its an import instruction by default. 
******************************************************/ 
#ifdef DLLDIR_EX
   #define DLLDIR  __declspec(dllexport)
#else
   #define DLLDIR  __declspec(dllimport)
#endif

extern "C" { 
       // We delete the function DLLfun1 (as defined 
       // in the W32DLL DLL) it writes to
       // a console, not a window, it isn't appropriate to 
       // call it from a MFC Client.
       int  DLLDIR DLLfun2(int);
       void DLLDIR DrawEllipse ( CRect, CDC* ); // a MFC function call 
}; 

extern int  DLLDIR DLLArg; 

class DLLDIR DLLclass
{
   public:
      DLLclass();          // Class Constructor
      ~DLLclass();         // Class destructor
      int Add(int, int);   // Class function Add
      int Sub(int, int);   // Class function Subtract
      int Arg;
};

Save and close this header file. Now we are going to create the DLLCode.cpp file. Select New from the File menu, then select "C++ Source File". Name the file: DLLCode. Click OK. Copy and paste the following code excerpt:

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/************************************************************
   File name: DLLCode.cpp 

   The header file, DLLCode.h, prototypes all 
   of the DLL interface objects 
*************************************************************/
#include "StdAfx.h"
#include "DLLCode.h" 

int DLLfun2(int a) { return a<<1; }; 

int DLLArg = 100; 

DLLclass::DLLclass() {}; 
DLLclass::~DLLclass() {}; 

int DLLclass::Add(int a, int b)
{
   return a + b;
}; 

int DLLclass::Sub(int a, int b)
{
   return a - b;
}; 

void DrawEllipse ( CRect rect, CDC *pDC )
{ 
 CBrush brush;
 brush.CreateSolidBrush(RGB(0,0,255));
 pDC->SelectObject(&brush); 
 pDC->Ellipse(&rect);
};

Now, select "setting..." from the Project menu. Select the C/C++ tab. Append, or insert, ",DLLDIR_EX" (without the quotation marks) to the Preprocessor Definition text box. Then click OK.

Click the "!" button to compile, build, and run the RDLLMFC project. Close the "Executable For Debug Session" dialog box, we ran the DLL prematurely. Congratulations, you finished building the Win32 DLL and its export Library.

Part Five, DLL MFC Client Application

This client application is a MFC application. It provides the framework, a window, for the MFC CBrush object used in the DLL function DrawEllipse.

Now, we are going to make the MFC application project MFCAp.

1. Close any open workspace and files, then select New from the File menu.
2. Select Project: MFC AppWizard(exe).
3. In the Project name box, give the project a fitting name, say, MFCAp, then click OK.
4. Select the "Single document" radio button, then click Finish and OK.

Select "ClassWizard..." from the View menu. The Message Maps tab should be active. In the "Class name:" dropdown box, select "CMFCApView". In the "Message functions:" list box, double click the "OnDraw" function label.

You should see the View class OnDraw function code. Replace that stub code with the following code excerpt, use copy and paste:

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///////////////////////////////////////////////
// CMFCApView drawing 

void CMFCApView::OnDraw(CDC* pDC)
{
   // DLL MFC Library function call
   CRect rect;
   rect.top=10;
   rect.left=10;
   rect.right=200;
   rect.bottom=200; 
   DrawEllipse(rect,pDC); 

   // DLL class object call
   int a, b, c;
   CString str;
   DLLclass classFromDLL; 
   classFromDLL.Arg = 6; 
   a = classFromDLL.Add(3, 2);
   b = classFromDLL.Sub(3, 2);
   c = classFromDLL.Arg;

   // Display data in window
   int y = 250, dy;
   TEXTMETRIC tm;
   pDC->GetTextMetrics(&tm);
   dy = tm.tmHeight + tm.tmExternalLeading; 
   str.Format("DLL class Add function return: %d", a);
   pDC->TextOut(20, y, str);
   y += dy;
   str.Format("DLL class Sub function return: %d", b);
   pDC->TextOut(20, y, str);
   y += dy;
   str.Format("DLL class Arg Variable return: %d", c);
   pDC->TextOut(20, y, str);
   y += dy; 
   a = DLLArg;
   b = DLLfun2(30); 
   str.Format("DLL class Arg Variable return: %d", a);
   pDC->TextOut(20, y, str);
   y += dy;
   str.Format("DLL function \"DLLfun2\" return: %d", b);
   pDC->TextOut(20, y, str);
}

At the top of the file MCFApView.cpp, and somewhere after the line containing: #include "stdafx.h", insert the following line:

#include "DLLCode.h"

Save and close the MFCApView.cpp file. Select "Setting..." from the Project menu. Select the "Link" tab. In the "Object/Library modules:" text box, enter: "RDLLMFC.lib", without the quotation marks. Then click OK.

Now, minimize the VC++ Studio window. Copy the following files to the MFCAp project directory:

• RDLLMFC\Debug\RDLLMFC.DLL
• RDLLMFC\Debug\RDLLMFC.lib
• RDLLMFC\DLLCode.h

Now maximize the VC++ Studio window, then click the "!" button.

A note in closing, you shouldn't change the DLL interface, especially class objects which are exported therein, because the v-table and class size are fitted at compile time. If you change the DLL and other programs are using it, you should rename the new version; or alternatively, you should re-compile all programs based on that DLL with the new interface.

Introduction

     In today's enterprises, different types of data are sitting in various data stores. Relational data is most likely to be in a SQL Server database or Oracle database. Many enterprise applications have their own database with its own data and data model. User and account information reside in a directory like Active Directory or Active Directory Application Mode. For more information about the directory services, please refer to the following article. Smaller, more fluent and mobile data sits in Excel spreadsheets or Microsoft Access databases. Each enterprise has large amounts of files like Word documents, Excel Spreadsheets, HTML documents, etc. which are sitting on a file system. It's a common practice to use Microsoft Indexing Server to index all the files sitting on the file system or a web server. Microsoft Indexing Server creates an indexing catalog and also provides a SQL query interface which enables you to simply search the index. For more information about Microsoft Indexing Server please refer to the following article.

The challenge enterprises are facing now is how to provide a complete and easy view into all this data sitting in various stores. More over how can you search all this data in various data sources without having to create many different interfaces or create complex search mechanisms? The good news is that most of these data stores provide a SQL query language. The SQL language varies slightly from one data source to another. For example directories like Active Directory provide a query capability but do not allow you to update, insert or delete data through SQL language. The same holds true for the SQL language of Microsoft Indexing Server. But most of the data sources provide the basic SQL query capability. Moreover Microsoft SQL Server allows you to link to other data stores which provide a SQL query language. This allows you to create a single SQL query spawning multiple data sources. This article explains how you can achieve this.

Linking other data stores to Microsoft SQL Server

Microsoft SQL Server provides the capability to link to other data sources which provide SQL query language. The Enterprise Manager of SQL Server shows in the left side navigation pane the "SQL Server groups" and under each all the database servers. It shows by default the local database server as "(local)". You can link other data stores to individual database servers. Expand a database server with the plus sign and you will find an entry called "Security". Expand the "Security" entry with the plus sign and you will see an entry called "Linked Servers". Expand the "Linked Servers" entry to see all the data stores which have been linked to this database server.

To link a new data store, right click on the entry "Linked Servers" and select "New Linked Server" from the popup menu. In the "Linked Server Properties" dialog you can enter a name for this linked server and then select whether you want to link another SQL Server database or any other data source. If you choose "SQL Server" then the linked server name must be the name of the SQL Server database you want to link to. For example if you have another SQL Server database running on the machine Enterprise-Minds then you would enter "Enterprise-Minds" as the linked server name. If you choose "Other data source" then you need to select from a list of existing data source providers, for example "Microsoft Jet 4.0 OLE Provider". Based on which provider you choose you need to enter the product name, data source, provider string, location and catalog. When you are done, click OK to create a link to this new data store. This new data source will now show up under "Linked Servers" with whatever name you had entered.

Link Microsoft SQL Server to a directory

You can link SQL Server to a directory like Active Directory or Active Directory Application Mode. Create a linked server in the Enterprise Manager and give it a descriptive name like "Active Directory Link". Choose the option "Other data source" and select the data provider "OLE DB Provider for Microsoft Directory Services". As product name enter "Active Directory Services" and as data source enter "adsdatasource". When you expand the new linked server you will find two available items - Tables and Views. So SQL Server allows you to view any tables or views in this data source. But the data provider "OLE DB Provider for Microsoft Directory Services" does not provide either the tables or views. Therefore you will get the error "Error 7301: Could not obtain a required interface from OLEDB provider ADsDSOObject". You can safely ignore the error message. You will be able to query the data store through the SQL query language.

It is important that you run the services "MSSQLSERVER" under an account which has access to the directory. If you run the services under the local system account you will get the following error when you try to query the data store:

Server: Msg 7321, Level 16, State 2, Line 1
An error occurred while preparing a query for 
         execution against OLE DB provider 'ADsDSOObject'.
OLE DB error trace [OLE/DB Provider 'ADsDSOObject' 
                    CommandPrepare::Prepare returned 0x80040e14].

So if the directory runs on your local machine and the local user "DirectoryUser" has access to it then you need to run the "MSSQLSERVER" service under this account. If the directory is running somewhere in your domain and the domain user "DomainUser" has access to it then you need to run the "MSSQLSERVER" service under this domain account.

Link Microsoft SQL Server to a Microsoft Indexing Server catalog

You can also link SQL Server to an Indexing Server catalog. Create a new linked server and give it a descriptive name, for example WEBCATALOG if you are linking to the Web Indexing Server catalog. Next select "Other data source" and choose as data provider "Microsoft OLE DB Provider for Indexing Service". Enter as product name "Index Server" and as data source the name of the Indexing Server catalog, for example Web. When you expand the new linked server you will find two available items - Tables and Views. So SQL Server allows you to view any tables or views in this data source. But the data provider "Microsoft OLE DB Provider for Indexing Service" neither provides the tables nor views. Therefore you will get an error "Error 7301: Could not obtain a required interface from OLEDB provider MSIDXS". You can safely ignore the error message. You will be able to query the data store through the SQL query language.

Link Microsoft SQL Server to a Microsoft Access database

SQL Server can also be linked to a Microsoft Access database. Create a new linked server and give it a descriptive name, for example "Booklist". Next select "Other data source" and choose as data provider "Microsoft Jet 4.0 OLE DB Provider". Enter as product name "Access" and as data source the path to Microsoft Access file, for example "c:\My files\Books.mdb". This data provider is able to show the list of tables and views. So when you expand the Table's or View's item under this linked server you will see the list of tables or views in the Microsoft Access database.

Link Microsoft SQL Server to a Microsoft Excel spreadsheet

SQL Server can also be linked to a Microsoft Excel spreadsheet. Create a new linked server and give it a descriptive name, for example "Booklist". Next select "Other data source" and choose as data provider "Microsoft Jet 4.0 OLE DB Provider". Enter as product name "Jet 4.0", as data source the path to the Microsoft Excel spreadsheet - for example "c:\My files\Books.xls" - and finally as provider string enter "Excel 5.0". This data provider shows under Tables the list of excel worksheets. It does not show any Views.

There are many other providers available, which allow you to link up SQL Server with a variety of different data sources. The following link lists some of the available data providers which can be used by SQL Server.

How to query linked servers?

Now we have learnt how to link SQL Server with a variety of different data stores. To query data from a linked server you can use the command OPENQUERY in your FROM clause, which means you can query data from a linked server instead of a standard SQL Server table or view. The command OPENQUERY requires two parameters. First is the name of the linked server followed by the query you want to execute against this linked server. The following example assumes that you have a linked server with the name Books which has a table called Books:

SELECT * FROM OPENQUERY(Books, 'SELECT * FROM Books') AS Books

The query you pass along in the OPENQUERY command needs to be supported by the linked data provider. So depending on the data provider it might vary slightly. You can join the data from any linked data source or SQL Server table together. The next example assumes that you query a linked data source and join it together with a SQL Server table called BookValue.

SELECT * FROM OPENQUERY(Books, 'SELECT * FROM Books') AS Books INNER JOIN 
BookValue ON Books.ID = BookValue.ID

How to query a directory?

The "OLE DB Provider for Microsoft Directory Services" accepts two different syntaxes. One is called the LDAP dialect and the other the SQL dialect . As its name suggests the SQL dialect follows the SQL language syntax. You specify for the SELECT keyword the directory attributes you want to query for. For the ORDER BY and WHERE keywords you specify the attributes to sort on and to filter by. And for the FROM keyword you specify which directory and directory container to query for. The following example queries the container "OU=Enterprise-Minds,CN=Vancouver" in the Enterprise-Minds directory. It returns the common name and returns only the directory objects of the type group.

SELECT * FROM OPENQUERY(ADAM,
  'SELECT cn FROM ''LDAP://Enterprise-Minds/OU=Enterprise-Minds,
   CN=Vancouver'' WHERE objectClass=''group'' ')

Please note that the FROM clause needs to be put under two single quotes (escape sequencing of single quotes within a string which is already under single quotes). The following example queries the common name and the ADS path for any directory object residing in the container "OU=Enterprise-Minds,CN=Vancouver" in the Enterprise-Minds directory.

SELECT * FROM OPENQUERY(ADAM,
 'SELECT cn, ADsPath FROM ''LDAP://Enterprise-Minds/OU=Enterprise-Minds,
  CN=Vancouver'' ')

The LDAP dialect consists of four parts, each separated by a semicolon. The first part specifies the directory and the directory container, the second part the filter, the third part the list of attributes to return and the last part the scope of the search. The scope part can have three values - Base, OneLevel and SubTree. Base searches only the directory path that you specify. OneLevel searches the immediate children of the directory path that you specify. And SubTree searches all the descendants of the directory path that you specify. The following example returns the same information as the first SQL dialect example - the list of all group objects:

SELECT * FROM OPENQUERY(ADAM,
  '<LDAP://Enterprise-Minds/OU=Enterprise-Minds,CN=Vancouver>;
  (objectClass=group);cn;subtree')

The next example returns the same information as the second SQL dialect example - the common name and the ADS path of all directory objects:

SELECT * FROM OPENQUERY(ADAM,
  '<LDAP://Enterprise-Minds/OU=Enterprise-Minds,CN=Vancouver>;;
  cn,ADsPath;subtree')

You can find more information about the possible filter syntaxes at the following article. The filter syntax applies for both dialects with the difference that the values need to be put under single quotes for the SQL dialect. For example you can see that the value group in the SQL dialect example is under single quotes (double single quotes for escape sequencing) while it is not for the LDAP dialect example.

How to query Indexing Server catalogs?

Please refer to the following article for a detailed explanation on how to query Indexing Server catalogs. The following example queries the file name, path and the virtual path for all files in the linked Web Indexing Server catalog.

SELECT * FROM OPENQUERY(WEBCATALOG, 'SELECT FileName, 
                            Path, VPath FROM SCOPE()')

The next example queries for all the files which contain the value "default" and are residing under the "/Info" virtual directory and all its sub directories. It returns for all matches the file name, path and virtual path.

SELECT * FROM OPENQUERY(WEBCATALOG, 'SELECT FileName, Path, VPath FROM 
  SCOPE(''DEEP TRAVERSAL OF("/Info")'') WHERE CONTAINS(FileName,''default'') ')

Please note that the value in the SCOPE function is under two single quotes for escape sequencing, while the value of the DEEP TRAVERSAL OF function is under double quotes, according to the Indexing Server SQL syntax. As shown you can create very complex queries.

How to query Excel spreadsheets?

All worksheets present in a linked Excel spreadsheet are shown as a tables. Note that all the table names show at the end a $ sign. Also if the worksheet name has spaces in it, you see the table name surrounded by single quotes which you always drop in your query. The table name in your query string needs to be surrounded by square brackets. The following example queries for all entries in the worksheet called Summary.

SELECT * FROM OPENQUERY(Books, 'SELECT * FROM [Summary$]')

It is important that the Excel spreadsheet is not open in Excel, otherwise you will get the following error:

Server: Msg 7399, Level 16, State 1, Line 1
OLE DB provider 'Microsoft.Jet.OLEDB.4.0' reported an error. 
    The provider did not give any information about the error.
OLE DB error trace [OLE/DB Provider 'Microsoft.Jet.OLEDB.4.0' 
    IDBInitialize::Initialize returned 0x80004005: The provider 
    did not give any information about the error.].

Introduction

This article provides two files that contain a Membership provider and a Role provider for ASP.NET v2.0.

Microsoft provides a Membership provider in the framework but only for SQL Server. The class does not seem to work for MySQL so I decided to write a new provider from the ODBC provider sample code included in the framework SDK.

How to use it

To use these classes, you will need the latest MySQL .NET Connector. You migh    （全文共9214字）——点击此处阅读全文