Why Use ADO?The use of ADO to transfer data to or retrieve data from an Excel workbook gives you, the developer, several advantages over Automation to Excel:
- Performance. Microsoft Excel is an out-of-process ActiveX server. ADO runs in-process, and saves the overhead of costly out-of-process calls.
- Scalability. For Web applications, it is not always desirable to automate Microsoft Excel. ADO presents you with a more scaleable solution to handle data in a workbook.
Jet OLE DB Provider Specifics for Excel WorkbooksThe Microsoft Jet database engine can be used to access data in other database file formats, such as Excel workbooks, through installable Indexed Sequential Access Method (ISAM) drivers. In order to open external formats supported by the Microsoft Jet 4.0 OLE DB Provider, you specify the database type in the extended properties for the connection. The Jet OLE DB Provider supports the following database types for Microsoft Excel workbooks:
- Excel 3.0
- Excel 4.0
- Excel 5.0
- Excel 8.0
The following samples demonstrate an ADO connection to an Excel 97 (or 2000) workbook:
Dim oConn As New ADODB.Connection
.Provider = "Microsoft.Jet.OLEDB.4.0"
.Properties("Extended Properties").Value = "Excel 8.0"
Dim oConn As New ADODB.Connection
oConn.Open "Provider=Microsoft.Jet.OLEDB.4.0;" & _
"Data Source=C:\Book1.xls;" & _
"Extended Properties=""Excel 8.0;"""
There are several ways you can reference a table (or range) in an Excel workbook:
- Use the sheet name followed by a dollar sign (for example, [Sheet1$] or [My Worksheet$]). A workbook table that is referenced in this manner consists of the entire used range of the worksheet.
oRS.Open "Select * from [Sheet1$]", oConn, adOpenStatic
- Use a range with a defined name (for example, [Table1]).
oRS.Open "Select * from Table1", oConn, adOpenStatic
- Use a range with a specific address (for example, [Sheet1$A1:B10]).
oRS.Open "Select * from [Sheet1$A1:B10]", oConn, adOpenStatic
With Excel workbooks, the first row in a range is considered to be the header row (or field names) by default. If the first range does not contain headers, you can specify HDR=NO in the extended properties in your connection string. If the first row does not contain headers, the OLE DB provider automatically names the fields for you (where F1 would represent the first field, F2 would represent the second field, and so forth).
Unlike a traditional database, there is no direct way to specify the data types for columns in Excel tables. Instead, the OLE DB provider scans a limited number of rows in a column to "guess" the data type for the field. The number of rows to scan defaults to eight (8) rows; you can change the number of rows to scan by specifying a value between one (1) and sixteen (16) for the MAXSCANROWS setting in the extended properties of your connection string.
Files Included with the SampleThe ExcelADO.exe file contains a Visual Basic Standard EXE project, Active Server Pages (ASP), Excel 97 and Excel 2000 Workbooks that act as templates, and a Microsoft Access 2000 database. The files included are as follows:
Visual Basic Standard EXE Project Files
How to Use the SampleExtract the contents of the .exe file to a folder.
To use the Visual Basic project:
- In Visual Basic, open the ExcelADO.vbp file.
- On the Project menu, select References, and then set references to Microsoft ADO Ext. for DDL and Security and Microsoft ActiveX Data Objects Library. This sample code works with both ADO 2.5 and ADO 2.6, so select the version appropriate to your computer.
- Press the F5 key to run the program. A form for the demonstration appears.
- Click Sample 1. This sample creates a copy of OrdersTemplate.xls. It then uses ADO to connect to the workbook and opens a Recordset on a table that is a defined range in the workbook. The name of the range is Orders_Table. It uses ADO AddNew/Update methods to add records (or rows) to the defined range in the workbook. When the row additions are complete, the ADO Connection is closed and the workbook is displayed in Microsoft Excel. Follow these steps to do this:
- On the Insert menu in Excel, select Names, and then select Define.
- In the list of defined names, select Orders_Table. Note that the defined name has grown to include the newly added records. The defined name is used, in conjunction with Excel's OFFSET function, to compute a total on the data added to the worksheet.
- Quit Microsoft Excel and return to the Visual Basic application.
- Click Sample 2. This sample creates a copy of EmpDataTemplate.xls. It uses ADO to connect to the workbook and uses the Execute method of the ADO connection to insert data (INSERT INTO in SQL) into the workbook. Data is added at defined ranges (or tables) in the workbook. When the data is transferred, the connection is closed and the workbook that results is displayed in Excel. After you examine the workbook, quit Microsoft Excel, and then return to the Visual Basic application.
- Click Sample 3. This sample creates a copy of ProductsTemplate.xls. It uses Microsoft ADO Extensions 2.1 for DDL and Security object library (ADOX) to add a new table (or a new worksheet) to the workbook. An ADO Recordset is then obtained for the new table and data is added by using the AddNew/Update methods. When the row additions are complete, the ADO Connection is closed and the workbook is displayed in Excel. The workbook contains Visual Basic for Applications (VBA) macro code in the Open event for the Workbook. The macro runs when the workbook opens; if the new "Products" worksheet exists in the workbook, the macro code formats the worksheet and then the macro code is deleted. This technique presents a way for the Web developer to move formatting code away from the Web server and onto the client. A Web application could stream a formatted workbook that contains data to the client and allow macro code that would perform any "conditional" formatting that might not be possible in a template alone to run at the client.
NOTE: To examine the macro code, view the ThisWorkbook module in the VBAProject for ProductsTemplate.xls.
- Click Sample 4. This sample produces the same results as Sample 1, but the technique that is used to transfer the data is slightly different. In Sample 1, records (or rows) are added to the worksheet one at a time. Sample 4 adds the records in bulk by attaching the Excel table to an Access database and running an append query (or INSERT INTO..SELECT FROM) to append records from a table in the Access table to the Excel table. Once the transfer is complete, the Excel table is detached from the Access database and the workbook that results is displayed in Excel. Quit Excel, and return to the Visual Basic application.
- The last sample illustrates how you can read data from an Excel workbook. Select a table in the drop-down list, and then click Sample 5. The Immediate window displays the contents of the table that you selected. If you select an entire worksheet ("Sheet1$" or "Sheet2$") for the table, the Immediate window displays the contents of the used range for that worksheet. Note that the used range does not necessarily begin on row 1, column 1 of the worksheet. The used range starts at the upper left-most cell in the worksheet that contains data.
If you select a specific range address or a defined range, the Immediate window displays the contents of only that range on the worksheet.
- Create a new folder named ExcelADO in the home directory of your Web server. Note that the default path for the home directory is C:\InetPut\WWWRoot.
- Copy the following files to the folder you created in the previous step:
- The ASP scripts in this sample create copies of the workbook templates with the Copy method of the FileSystemObject. For the Copy method to succeed, the client that is accessing the script must have Write access to the folder that contains the ASP.
- Navigate to Orders.asp (that is, http://YourServer/ExcelADO/Orders.ASP), and note that the browser displays an Excel workbook similar to the one in Sample 1 of the Visual Basic application.
- Navigate to EmpData.asp (that is, http://YourServer/ExcelADO/EmpData.ASP), and note that the browser displays an Excel workbook similar to the one in Sample 2 of the Visual Basic application.
(c) Microsoft Corporation 2000, All Rights Reserved. Contributions by Lori B. Turner, Microsoft Corporation.
ID článku: 278973 - Poslední kontrola: 21. 8. 2012 - Revize: 1