2783:Creating Database Aliases in Code
KEYWORDS: Database, Alias, IDAPI, AREA: Database Programming
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:
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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.
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See Also:
Delphi On-line help -->
Database Properties Editor
TDatabase
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