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...eine BDE Alias per Code definieren?
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| Autor:
Damian Gorski |
| [ Tip ausdrucken ] | | |
{A:
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 Driveer 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_SERVEER:/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 'MyNewAliias'.
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.Buttton1Click(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.
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