如何程序建立别名
编号：QA000751
建立日期: 1999年4月3日 最后修改日期：1999年4月3日
所属类别：
凌云:
请问如何程序建立别名?
回答:
下面这篇文章是来自Inprise(Borland)，它全面地介绍了有关别名的问题。
This Technical Information document will help step thru concepts regarding the creation and use of ALIASES within your Delphi Applications.
Typically, you use the BDE Configuration Utility BDECFG.EXE to create and configure aliases outside of Delphi. However, with the use of the TDatabase component, you have the ability to create and use this ALIAS within your application-- not pre-defined in the IDAPI.CFG.
The ability to create Aliases that are only available within your application is important. Aliases specify the location of database tables and connection parameters for database servers. Ultimately, you can gain the advantages of using ALIASES within
your applications-- without having to worry about the existance of a configuration entry in the IDAPI.CFG when you deploy your application.
Summary of Examples:
------- -- ---------
Example #1:
Example #1 creates and configures an Alias to use STANDARD (.DB, .DBF) databases. The Alias is then used by a TTable component.
Example #2:
Example #2 creates and configures an Alias to use an INTERBASE database (.gdb). The Alias is then used by a TQuery component to join two tables of the database.
Example #3:
Example #3 creates and configures an Alias to use STANDARD (.DB, .DBF) databases. This example demonstrates how user input can be used to configure the Alias during run-time.
Example #1: Use of a .DB or .DBF database (STANDARD)
1. Create a New Project.
2. Place the following components on the form:
- TDatabase, TTable, TDataSource, TDBGrid, and TButton
3. Double-click on the TDatabase component or choose Database Editor from the TDatabase SpeedMenu to launch the Database Property editor.
4. Set the Database Name to 'MyNewAlias'. This name will serve as your ALIAS name used in the DatabaseName Property for dataset components such as TTable, TQuery, TStoredProc.
5. Select STANDARD as the Driver Name.
6. Click on the Defaults Button. This will automatically add a PATH= in the Parameter Overrides section.
7. Set the PATH= to C:\DELPHI\DEMOS\DATA (PATH=C:\DELPHI\DEMOS\DATA)
8. Click the OK button to close the Database Dialog.
9. Set the TTable DatabaseName Property to 'MyNewAlias'.
10. Set the TDataSource's DataSet Property to 'Table1'.
11. Set the DBGrid's DataSource Property to 'DataSource1'.
12. Place the following code inside of the TButton's OnClick event.
procedure TForm1.Button1Click(Sender: TObject);
begin
Table1.Tablename:= 'CUSTOMER';
Table1.Active:= True;
end;
13. Run the application.
*** If you want an alternative way to steps 3 - 11, place the following code inside of the TButton's OnClick event.
procedure TForm1.Button1Click(Sender: TObject);
begin
Database1.DatabaseName:= 'MyNewAlias';
Database1.DriverName:= 'STANDARD';
Database1.Params.Clear;
Database1.Params.Add('PATH=C:\DELPHI\DEMOS\DATA');
Table1.DatabaseName:= 'MyNewAlias';
Table1.TableName:= 'CUSTOMER';
Table1.Active:= True;
DataSource1.DataSet:= Table1;
DBGrid1.DataSource:= DataSource1;
end;
*****
Example #2: Use of a INTERBASE database
1. Create a New Project.
2. Place the following components on the form:
- TDatabase, TQuery, TDataSource, TDBGrid, and TButton
3. Double-click on the TDatabase component or choose Database Editor from the TDatabase SpeedMenu to launch the Database Property editor.
4. Set the Database Name to 'MyNewAlias'. This name will serve as your ALIAS name used in the DatabaseName Property for dataset components such as TTable, TQuery, TStoredProc.
5. Select INTRBASE as the Driver Name.
6. Click on the Defaults Button. This will automatically add the following entries in the Parameter Overrides section.
SERVER NAME=IB_SERVER:/PATH/DATABASE.GDB
USER NAME=MYNAME
OPEN MODE=READ/WRITE
SCHEMA CACHE SIZE=8
LANGDRIVER=
SQLQRYMODE=
SQLPASSTHRU MODE=NOT SHARED
SCHEMA CACHE TIME=-1
PASSWORD=
7. Set the following parameters
SERVER NAME=C:\IBLOCAL\EXAMPLES\EMPLOYEE.GDB
USER NAME=SYSDBA
OPEN MODE=READ/WRITE
SCHEMA CACHE SIZE=8
LANGDRIVER=
SQLQRYMODE=
SQLPASSTHRU MODE=NOT SHARED
SCHEMA CACHE TIME=-1
PASSWORD=masterkey
8. Set the TDatabase LoginPrompt Property to 'False'. If you supply the PASSWORD in the Parameter Overrides section and set the LoginPrompt to 'False', you will not be prompted for the password when connecting to the database. WARNING: If an
incorrect password in entered in the Parameter Overrides section and LoginPrompt is set to 'False', you are not prompted by the Password dialog to re-enter a valid password.
9. Click the OK button to close the Database Dialog.
10. Set the TQuery DatabaseName Property to 'MyNewAlias'.
11. Set the TDataSource's DataSet Property to 'Query1'.
12. Set the DBGrid's DataSource Property to 'DataSource1'.
13. Place the following code inside of the TButton's OnClick event.
procedure TForm1.Button1Click(Sender: TObject);
begin
Query1.SQL.Clear;
Query1.SQL.ADD(
'SELECT DISTINCT * FROM CUSTOMER C, SALES S
WHERE (S.CUST_NO = C.CUST_NO)
ORDER BY C.CUST_NO, C.CUSTOMER');
Query1.Active:= True;
end;
14. Run the application.
Example #3: User-defined Alias Configuration
This example brings up a input dialog and prompts the user to enter the directory to which the ALIAS is to be configured to.
The directory, servername, path, database name, and other neccessary Alias parameters can be read into the application from use of an input dialog or .INI file.
1. Follow the steps (1-11) in Example #1.
2. Place the following code inside of the TButton's OnClick event.
procedure TForm1.Button1Click(Sender: TObject);
var
NewString: string;
ClickedOK: Boolean;
begin
NewString := 'C:\';
ClickedOK := InputQuery('Database Path',
'Path: --> C:\DELPHI\DEMOS\DATA', NewString);
if ClickedOK then
begin
Database1.DatabaseName:= 'MyNewAlias';
Database1.DriverName:= 'STANDARD';
Database1.Params.Clear;
Database1.Params.Add('Path=' + NewString);
Table1.DatabaseName:= 'MyNewAlias';
Table1.TableName:= 'CUSTOMER';
Table1.Active:= True;
DataSource1.DataSet:= Table1;
DBGrid1.DataSource:= DataSource1;
end;
end;
3. Run the Application.
此问题由李海回答。
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