SQLdb Tutorial2: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: SQLdb Tutorial2

New		Line
1	+	## Overview
2	+
3	+	If you have followed [[SQLdb Tutorial1]], you have a basic grid showing database information. While this application works, we can add some refinements on this.
4	+
5	+	### Dynamic database connection
6	+
7	+	Up to now, we used a fixed database server name, database location, username and password for simplicity. As mentioned, "real" applications normally let users specify their own username and password.
8	+
9	+	Let's change the form so we can specify them: add two [[TEdit\|TEdits]] from the standard menu. Set their name properties to Username and Password. Set the Password's PasswordChar property to * (the asterisk) for some security against people looking over your shoulder.
10	+
11	+	If you want to make it easier (and less secure, of course) to connect, you can set the UserName Text property to a valid database user, such as SYSDBA. You could even set the Password Text property to a default value like masterkey, easy for testing on developer machines if security doesn't matter...
12	+
13	+	Cosmetically, adding some labels so people know what they're supposed to type is useful.
14	+
15	+	Also, to make it easier to connect to any employee sample database on any Firebird/Interbase server, we add two textboxes for server name and database path. Add another two TEdits, and name them ServerName and DatabaseName.
16	+
17	+	If you want, you can set the 'Text' property to default sensible values for your situation, e.g. localhost and `C:\Program Files\Firebird\Firebird_2_5\examples\empbuild\EMPLOYEE.FDB`
18	+
19	+	Labels to explain what users need to enter would help here, too.
20	+
21	+	For clarity, we're going to remove the connection info from our design time components: on the [[TSQLConnector]] component, remove all text from the UserName, Password, DatabaseName and HostName properties.
22	+
23	+	Now, finally, we need to tell our database connection component how to connect. This should normally only be necessary at the beginning of an application run. In our case the existing 'Button1' code is a good way to set up the connection.
24	+
25	+	Add code until you get:
26	+
27	+	``` pascal
28	+	procedure TForm1.Button1Click(Sender: TObject);
29	+	begin
30	+	SQLQuery1.Close;
31	+	//Connection settings for Firebird/Interbase database
32	+	//only needed when we have not yet connected:
33	+	if not DBConnection.Connected then
34	+	begin
35	+	DBConnection.HostName := ServerName.Text;
36	+	DBConnection.DatabaseName := DatabaseName.Text;
37	+	DBConnection.Username := UserName.Text;
38	+	DBConnection.Password := Password.Text;
39	+	// Now we've set up our connection, visually show that
40	+	// changes are not possibly any more
41	+	ServerName.ReadOnly:=true;
42	+	DatabaseName.ReadOnly:=true;
43	+	UserName.ReadOnly:=true;
44	+	Password.ReadOnly:=true;
45	+	end;
46	+	SQLQuery1.SQL.Text:= 'select * from CUSTOMER';
47	+	DBConnection.Connected:= True;
48	+	SQLTransaction1.Active:= True;
49	+	SQLQuery1.Open;
50	+	end;
51	+	```
52	+
53	+	Now run and test if you can connect.
54	+
55	+	#### SQLite, other databases
56	+
57	+	Adjust the Text property in the DatabaseName TEdit as needed; e.g. `employee.sqlite` for SQLite.
58	+
59	+	For sqlite, specifying HostName, Username and Password doesn't make sense, so you can omit these TEdits. Obviously, leave out/comment out assigning the corresponding values to DBConnection in the code above. For Firebird embedded, please hardcode the Username to SYSDBA; specifying this when sqlite is used won't hurt.
60	+
61	+	The code will look something like:
62	+
63	+	``` pascal
64	+	procedure TForm1.Button1Click(Sender: TObject);
65	+	begin
66	+	SQLQuery1.Close;
67	+	//Connection settings for embedded databases
68	+	//only needed when we have not yet connected:
69	+	if not DBConnection.Connected then
70	+	begin
71	+	DBConnection.DatabaseName := DatabaseName.Text;
72	+	DBConnection.UserName := 'SYSDBA'; //Firebird embedded needs this; doesn't harm if using SQLite
73	+	// Now we've set up our connection, visually show that
74	+	// changes are not possibly any more
75	+	DatabaseName.ReadOnly:=true;
76	+	end;
77	+	SQLQuery1.SQL.Text:= 'select * from CUSTOMER';
78	+	DBConnection.Connected:= True;
79	+	SQLTransaction1.Active:= True;
80	+	SQLQuery1.Open;
81	+	end;
82	+	```
83	+
84	+	### Filtering data
85	+
86	+	Often, tables contain a huge amount of data that the user doesn't want to see (and that might take a long time to query from the database and travel over the network). Let's assume that only the customers from the USA should be displayed. Therefore the SQL instruction in 'SQLQuery1' would look like:
87	+
88	+	``` SQL
89	+	select * from CUSTOMER where COUNTRY = 'USA'
90	+	```
91	+
92	+	... which would translate to something like this in our code:
93	+
94	+	``` pascal
95	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER where COUNTRY = 'USA'';
96	+	```
97	+
98	+	There are two reasons why we will not use this instruction for our example application:
99	+
100	+	First there is a problem with the usage of the single quote. The compiler would interpret the quote before USA as a closing quote (the first quote is before the select from...) and so the SQL instruction would become invalid. Solution: double the inside quotes:
101	+
102	+	``` pascal
103	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER where COUNTRY = ''USA''';
104	+	```
105	+
106	+	The second, more important reason is the fact, that we probably don't know what constraints the user will want to filter on. We don't want to limit the flexibility of the user.
107	+
108	+	To get this flexibility, first we change our SQL query statement and replace 'USA' by a placeholder (a parameter in SQL speak): change the Button1click procedure and replace:
109	+
110	+	``` pascal
111	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER';
112	+	```
113	+
114	+	with:
115	+
116	+	``` pascal
117	+	SQLQuery1.SQL.Text:= 'select * from CUSTOMER where COUNTRY = :COUNTRY';
118	+	```
119	+
120	+	In FPC SQLDB, the SQL parameter is marked by the leading colon (other languages/environments use other conventions like ?). To allow the user to enter a value for the filter, we place a TEdit component on our form. Delete the value of its 'Text' property.
121	+
122	+	We can now take the text entered in the TEdit and fill the SQL COUNTRY parameter by using the 'Params' property of TSQLQuery. Add this below the previous statement:
123	+
124	+	``` pascal
125	+	SQLQuery1.Params.ParamByName('COUNTRY').AsString := Edit1.Text;
126	+	```
127	+
128	+	The parameter can be specified by its position or name. Using the name should improve the readability of the source code, and obviously helps if you insert more parameters in the middle of existing parameters.
129	+
130	+	We use .AsString to assign a string value to the parameter; there are equivalent property assignments for integer parameters, boolean parameters etc.
131	+
132	+	The code up to now forces us to use a filter. If a user specifies an empty value in the edit box, no record will be displayed. This is probably not what we want. Let's test for an empty value and build our query accordingly. We should end up with a procedure like this:
133	+
134	+	``` pascal
135	+	procedure TForm1.Button1Click(Sender: TObject);
136	+	begin
137	+	SQLQuery1.Close;
138	+	//Connection settings for Firebird/Interbase database
139	+	//only needed when we have not yet connected:
140	+	if not DBConnection.Connected then
141	+	begin
142	+	DBConnection.HostName := ServerName.Text;
143	+	DBConnection.DatabaseName := DatabaseName.Text;
144	+	DBConnection.Username := UserName.Text;
145	+	DBConnection.Password := Password.Text;
146	+	// Now we've set up our connection, visually show that
147	+	// changes are not possibly any more
148	+	ServerName.ReadOnly:=true;
149	+	DatabaseName.ReadOnly:=true;
150	+	UserName.ReadOnly:=true;
151	+	Password.ReadOnly:=true;
152	+	end;
153	+	// Show all records, or filter if user specified a filter criterium
154	+	if Edit1.Text='' then
155	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER'
156	+	else
157	+	begin
158	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER where COUNTRY = :COUNTRY';
159	+	SQLQuery1.Params.ParamByName('COUNTRY').AsString := Edit1.Text;
160	+	end;
161	+	DBConnection.Connected:= True;
162	+	SQLTransaction1.Active:= True;
163	+	SQLQuery1.Open;
164	+	end;
165	+	```
166	+
167	+	Now you can play around a bit with filtering using Edit1. If you enter a country that's not present in the database, an empty grid is shown.
168	+
169	+	### Error handling
170	+
171	+	The application should run, but sometimes problems can occur. Databases, even embedded databases can crash (e.g. when the database server crashes, the disk is full, or just due to a bug), leaving the application hanging.
172	+
173	+	Access to a database (any external process, really) should therefore always be integrated in a try ... except and/or try ... finally construct. This ensures that database errors are handled and the user isn't left out in the cold. A rudimentary routine for our example application could look like this:
174	+
175	+	``` pascal
176	+	begin
177	+	try
178	+	SQLQuery1.Close;
179	+	...
180	+	SQLQuery1.Open;
181	+	except
182	+	//We could use EDatabaseError which is a general database error, but we're dealing with Firebird/Interbase, so:
183	+	on E: EDatabaseError do
184	+	begin
185	+	MessageDlg('Error','A database error has occurred. Technical error message: ' + E.Message,mtError,[mbOK],0);
186	+	Edit1.Text:='';
187	+	end;
188	+	end;
189	+	end;
190	+	```
191	+
192	+	#### SQLite, PostgreSQL, other databases
193	+
194	+	You can either use the more generic EDatabaseError, or - if available - your own specialized databaseerror, if you need more details. E.g. SQLite and the PostgreSQL driver in FPC 2.6.1 and lower doesn't have a specialized E*DatabaseError; you'd have to use EDatabaseError. PostgreSQL on FPC trunk (development version) has EPQDatabaseError.
195	+
196	+	## Editing data using the grid
197	+
198	+	### Editing
199	+
200	+	Up to now, if you tried to edit data in the grid, the changes would not be saved. This is because the SQLQuery1 is not instructed to send the changes to the database transaction at the right moment. We need to fix this, and then commit the transaction in the database, so all changes get written. For this, you would use code like this:
201	+
202	+	``` pascal
203	+	SQLQuery1.ApplyUpdates; //Pass user-generated changes back to database...
204	+	SQLTransaction1.Commit; //... and commit them using the transaction.
205	+	//SQLTransaction1.Active now is false
206	+	```
207	+
208	+	We want to make sure any edits (inserts, updates, deletes) are written to the database:
209	+
210	+	- when the users changes the filtering criteria and presses the button to query the database
211	+	- when the form is closed
212	+
213	+	It makes sense to make a separate procedure for this that is called in those two instances. Go to the code, and add an empty line here:
214	+
215	+	``` pascal
216	+	TForm1 = class(TForm)
217	+	Button1: TButton;
218	+	Datasource1: TDatasource;
219	+	DBGrid1: TDBGrid;
220	+	Edit1: TEdit;
221	+	DBConnection: TIBConnection;
222	+	SQLQuery1: TSQLQuery;
223	+	SQLTransaction1: TSQLTransaction;
224	+	***insert the empty line here**
225	+	procedure Button1click(Sender: TObject);
226	+	procedure Formclose(Sender: TObject; var Closeaction: Tcloseaction);
227	+	private
228	+	```
229	+
230	+	then type:
231	+
232	+	``` pascal
233	+	procedure SaveChanges;
234	+	```
235	+
236	+	press shift-ctrl-c (default combination) to let code completion automatically create the corresponding procedure body.
237	+
238	+	We need to add error handling and check that the transaction is active - remember, this code also gets called when pressing the button the first time, when the transaction is not active yet. We get:
239	+
240	+	``` pascal
241	+	procedure Tform1.SaveChanges;
242	+	// Saves edits done by user, if any.
243	+	begin
244	+	try
245	+	if SQLTransaction1.Active then
246	+	// Only if we are within a started transaction;
247	+	// otherwise you get "Operation cannot be performed on an inactive dataset"
248	+	begin
249	+	SQLQuery1.ApplyUpdates; //Pass user-generated changes back to database...
250	+	SQLTransaction1.Commit; //... and commit them using the transaction.
251	+	//SQLTransaction1.Active now is false
252	+	end;
253	+	except
254	+	on E: EDatabaseError do
255	+	begin
256	+	SQLTransaction1.Rollback;
257	+	MessageDlg('Error', 'A database error has occurred. Technical error message: ' +
258	+	E.Message, mtError, [mbOK], 0);
259	+	Edit1.Text := '';
260	+	end;
261	+	end;
262	+	end;
263	+	```
264	+
265	+	Now we need to call this procedure at the appropriate moments:
266	+
267	+	``` pascal
268	+	procedure Tform1.Button1click(Sender: TObject);
269	+	begin
270	+	SaveChanges; //Saves changes and commits transaction
271	+	try
272	+	SQLQuery1.Close;
273	+	....
274	+	```
275	+
276	+	and:
277	+
278	+	``` pascal
279	+	procedure Tform1.Formclose(Sender: TObject; var Closeaction: Tcloseaction);
280	+	begin
281	+	SaveChanges; //Saves changes and commits transaction
282	+	SQLQuery1.Close;
283	+	....
284	+	```
285	+
286	+	Now test and see if edits made in the dbgrid are saved to the database.
287	+
288	+	### Hiding primary key column
289	+
290	+	Often, you don't want your users to see autonumber/generated primary keys as they are only meant to maintain referential integrity. If users do see them, they might want to try the edit the numbers, get upset that the numbers change, that there are gaps in the numbers, etc.
291	+
292	+	In our example, CUST_NO is the primary key, with content auto-generated by Firebird using triggers and a sequence/generator. This means that you can insert a new record without specifying the CUST_NO; Firebird will create one automatically.
293	+
294	+	We could simply change our SQLQuery1.SQL.Text property to not include CUST_NO, but this would lead to problems when editing data - a primary key is needed in those circumstances for uniquely identifying the row/record in question.
295	+
296	+	Therefore, let's use a trick to query for all columns/fields in the table, but keep the grid from showing the first field, CUST_NO: in the Button1Click procedure, add code so it looks like:
297	+
298	+	``` pascal
299	+	procedure Tform1.Button1click(Sender: TObject);
300	+	begin
301	+	...
302	+	SQLQuery1.Open;
303	+	// Hide the primary key column which is the first column in our queries.
304	+	// We can only do this once the DBGrid has created the columns
305	+	DBGrid1.Columns[0].Visible:=false;
306	+	```
307	+
308	+	Recompile, and check to see if the primary key column is really hidden.
309	+
310	+	#### SQLite, other databases
311	+
312	+	- Other databases: a lot of other databases use an 'autonumber' or 'autoinc' type of field to provide auto-generated field content. Try changing your table definition and see if it works.
313	+	- Sqlite: the example above works for SQLite as is because we're using an integer primary key. See the [documentation](http://www.sqlite.org/autoinc.html) for details.
314	+
315	+	### Inserting new data
316	+
317	+	If you insert new rows/records without any CUST_NO information you may have noticed that you get an error message: `Field CUST_NO is required, but not supplied`. This also happens if you hid the CUST_NO column, as in the previous section.
318	+
319	+	The reason: Lazarus thinks that CUST_NO is required. That's not so strange, because it is a primary key and the underlying table definition in the database does say it is required.
320	+
321	+	If we can instruct Lazarus that this field is not actually required, we can pass empty values (=NULL values) to the database. Fortunately, a query's field object has a Required property that does exactly that.
322	+
323	+	Change the code to something like:
324	+
325	+	``` pascal
326	+	SQLQuery1.Open;
327	+	{
328	+	Make sure we don't get problems with inserting blank (=NULL) CUST_NO values, e.g.:
329	+	Field CUST_NO is required, but not supplied
330	+	We need to tell Lazarus that, while CUST_NO is a primary key, it is not required
331	+	when inserting new records.
332	+	}
333	+	SQLQuery1.FieldByName('CUST_NO').Required:=false;
334	+	// Hide the primary key column which is the first column in our queries.
335	+	// We can only do this once the DBGrid has created the columns
336	+	DBGrid1.Columns[0].Visible:=false;
337	+	```
338	+
339	+	### Deleting data
340	+
341	+	You can let your users use the mouse to do this. You don't even need to code a single line for this functionality...
342	+
343	+	On the 'Data Controls' tab, select a TDBNavigator component and drop it on the form, above the grid.
344	+
345	+	To indicate what the navigator should be linked to, set its DataSource property to your existing datasource ('DataSource1') using the Object Inspector. Now you can use the button on the DBNavigator to delete records, but also insert them, and move around the records. Also, when editing cells/fields, you can use the Cancel button to cancel your edits.
346	+
347	+	To allow users to delete the row they're in on the grid using the <span class="kbd">Delete</span> key, add LCLType (this contains definitions for key codes) to your uses clause:
348	+
349	+	``` pascal
350	+	uses
351	+	Classes, SysUtils, sqldb, pqconnection, DB, FileUtil, Forms,
352	+	Controls, Graphics, Dialogs, DBGrids, StdCtrls, DbCtrls, LCLType;
353	+	```
354	+
355	+	... then handle the KeyUp event for the grid, which occurs when a key is released if in the grid. However, we do need to check that the user is not editing a field - as he'll probably use the <span class="kbd">Delete</span> key to delete letters rather than the record he's working on.
356	+
357	+	Select the grid, then go to events and create an OnKeyUp event like this:
358	+
359	+	``` pascal
360	+	procedure TForm1.DBGrid1KeyUp(Sender: TObject; var Key: Word; Shift: TShiftState
361	+	);
362	+	begin
363	+	// Check for del key being hit and delete the current record in response
364	+	// as long as we're not editing data
365	+	if (key=VK_DELETE) and (not(DBGrid1.EditorMode)) then
366	+	begin
367	+	//... delete current record and apply updates to db:
368	+	SQLQuery1.Delete;
369	+	SQLQuery1.ApplyUpdates;
370	+	end;
371	+	end;
372	+	```
373	+
374	+	> Note: By default TDBGrid property Options / dgDisableDelete is set to false, this means a user can delete any record with the <span class="kbd">ctrl</span>-<span class="kbd">delete</span> key combo. You may not want this behaviour.
375	+
376	+	## Summary
377	+
378	+	If you followed along up to now, you can retrieve data from the database, filter it, and edit and delete data in the grid. Your code should look something like this:
379	+
380	+	``` pascal
381	+	unit sqldbtutorial1unit;
382	+
383	+	{$mode objfpc}{$H+}
384	+
385	+	interface
386	+
387	+	uses
388	+	Classes, SysUtils, sqldb, pqconnection, DB, FileUtil, Forms,
389	+	Controls, Graphics, Dialogs, DBGrids, StdCtrls, DbCtrls, LCLType;
390	+	type
391	+
392	+	{ TForm1 }
393	+
394	+	TForm1 = class(TForm)
395	+	Button1: TButton;
396	+	DatabaseName: TEdit;
397	+	Datasource1: TDatasource;
398	+	DBGrid1: TDBGrid;
399	+	Dbnavigator1: Tdbnavigator;
400	+	Edit1: TEdit;
401	+	Label2: Tlabel;
402	+	Label3: Tlabel;
403	+	Label4: Tlabel;
404	+	Label5: Tlabel;
405	+	Password: TEdit;
406	+	UserName: TEdit;
407	+	ServerName: TEdit;
408	+	DBConnection: TIBConnection;
409	+	Label1: TLabel;
410	+	SQLQuery1: TSQLQuery;
411	+	SQLTransaction1: TSQLTransaction;
412	+	procedure SaveChanges;
413	+	procedure Button1click(Sender: TObject);
414	+	procedure Formclose(Sender: TObject; var Closeaction: Tcloseaction);
415	+	private
416	+	{ private declarations }
417	+	public
418	+	{ public declarations }
419	+	end;
420	+
421	+	var
422	+	Form1: TForm1;
423	+
424	+	implementation
425	+
426	+	{$R *.lfm}
427	+
428	+	{ TForm1 }
429	+
430	+	procedure Tform1.Savechanges;
431	+	// Saves edits done by user, if any.
432	+	begin
433	+	try
434	+	if SQLTransaction1.Active then
435	+	// Only if we are within a started transaction
436	+	// otherwise you get "Operation cannot be performed on an inactive dataset"
437	+	begin
438	+	SQLQuery1.ApplyUpdates; //Pass user-generated changes back to database...
439	+	SQLTransaction1.Commit; //... and commit them using the transaction.
440	+	//SQLTransaction1.Active now is false
441	+	end;
442	+	except
443	+	on E: EDatabaseError do
444	+	begin
445	+	SQLTransaction1.Rollback;
446	+	MessageDlg('Error', 'A database error has occurred. Technical error message: ' +
447	+	E.Message, mtError, [mbOK], 0);
448	+	Edit1.Text := '';
449	+	end;
450	+	end;
451	+	end;
452	+
453	+	procedure TForm1.DBGrid1KeyUp(Sender: TObject; var Key: Word; Shift: TShiftState
454	+	);
455	+	begin
456	+	// Check for del key being hit and delete the current record in response
457	+	// as long as we're not editing data
458	+	if (key=VK_DELETE) and (not(DBGrid1.EditorMode)) then
459	+	begin
460	+	//... delete current record and apply updates to db:
461	+	SQLQuery1.Delete;
462	+	SQLQuery1.ApplyUpdates;
463	+	end;
464	+	end;
465	+
466	+	procedure Tform1.Button1click(Sender: TObject);
467	+	begin
468	+	SaveChanges; //Saves changes and commits transaction
469	+	try
470	+	SQLQuery1.Close;
471	+	//Connection settings for Firebird/Interbase database
472	+	//only needed when we have not yet connected:
473	+	if not DBConnection.Connected then
474	+	begin
475	+	DBConnection.HostName := ServerName.Text;
476	+	DBConnection.DatabaseName := DatabaseName.Text;
477	+	DBConnection.Username := UserName.Text;
478	+	DBConnection.Password := Password.Text;
479	+	// Now we've set up our connection, visually show that
480	+	// changes are not possibly any more
481	+	ServerName.ReadOnly:=true;
482	+	DatabaseName.ReadOnly:=true;
483	+	UserName.ReadOnly:=true;
484	+	Password.ReadOnly:=true;
485	+	end;
486	+	// Show all records, or filter if user specified a filter criterium
487	+	if Edit1.Text='' then
488	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER'
489	+	else
490	+	begin
491	+	SQLQuery1.SQL.Text := 'select * from CUSTOMER where COUNTRY = :COUNTRY';
492	+	SQLQuery1.Params.ParamByName('COUNTRY').AsString := Edit1.Text;
493	+	end;
494	+	DBConnection.Connected := True;
495	+	SQLTransaction1.Active := True; //Starts a new transaction
496	+	SQLQuery1.Open;
497	+	{
498	+	Make sure we don't get problems with inserting blank (=NULL) CUST_NO values, i.e. error message:
499	+	"Field CUST_NO is required, but not supplied"
500	+	We need to tell Lazarus that, while CUST_NO is a primary key, it is not required
501	+	when inserting new records.
502	+	}
503	+	SQLQuery1.FieldByName('CUST_NO').Required:=false;
504	+	{
505	+	Hide the primary key column which is the first column in our queries.
506	+	We can only do this once the DBGrid has created the columns
507	+	}
508	+	DBGrid1.Columns[0].Visible:=false;
509	+	except
510	+	// EDatabaseError is a general error;
511	+	// you could also use one for your specific db, e.g.
512	+	// use EIBDatabaseError for Firebird/Interbase
513	+	on E: EDatabaseError do
514	+	begin
515	+	MessageDlg('Error', 'A database error has occurred. Technical error message: ' +
516	+	E.Message, mtError, [mbOK], 0);
517	+	Edit1.Text := '';
518	+	end;
519	+	end;
520	+	end;
521	+
522	+	procedure Tform1.Formclose(Sender: TObject; var Closeaction: Tcloseaction);
523	+	begin
524	+	SaveChanges; //Saves changes and commits transaction
525	+	SQLQuery1.Close;
526	+	SQLTransaction1.Active := False;
527	+	DBConnection.Connected := False;
528	+	end;
529	+
530	+	end.
531	+	```
532	+
533	+	## Embedded database without code changes
534	+
535	+	### Firebird on Windows
536	+
537	+	A bonus for Firebird users on Windows: if you have been following this tutorial (even if you only did the basic example), you renamed the `fbembed.dll` embedded Firebird library to `fbclient.dll`. With this, Lazarus could connect to regular Firebird servers (either on another machine or on your local machine). However, you can also copy the `employee.fdb` database to your application directory, run the application, clear the Server name TEdit and use Firebird embedded to directly connect to the database file, without any servers set up.
538	+
539	+	This is great if you want to deploy database applications to end users, but don't want the hassle of installing servers (checking if a server is already installed, if it's the right version, having users check firewalls, etc).
540	+
541	+	See [[Firebird embedded]] for more details.
542	+
543	+	September 2011: in recent development (SVN) versions of Free Pascal, FPC tries to first load `fbembed.dll`, so you need not rename `fbclient.dll` anymore for this to work.
544	+
545	+	### Firebird on Linux/macOS/Unix
546	+
547	+	There must be a way to get this to work on Linux/macOS. See [[Firebird]] for hints and links. Updates to the wiki are welcome.
548	+
549	+	### SQLite
550	+
551	+	SQLite certainly offers embedded functionality - it does not allow a client/server setup on the other hand. By following the tutorial above, you can see that switching between databases (e.g. SQLite and Firebird) is not so much work at all.
552	+
553	+	### Other databases
554	+
555	+	Your database might offer similar functionality. Updates of this wiki for other database systems are welcome.
556	+
557	+	## See also
558	+
559	+	- [[SQLdb Tutorial0]]: Instructions for setting up sample tables/sample data for the tutorial series.
560	+	- [[SQLdb Tutorial1]]: First part of the DB tutorial series, showing how to set up a grid that shows database data
561	+	- [[SQLdb Tutorial3]]: Third part of the DB tutorial series, showing how to program for multiple databases and use a login form
562	+	- [[SQLdb Tutorial4]]: Fourth part of the DB tutorial series, showing how to use data modules
563	+	- [[Lazarus Database Overview]]: Information about the databases that Lazarus supports. Links to database-specific notes.
564	+	- [[SQLdb Package]]: information about the SQLdb package
565	+	- [[SQLdb Programming Reference]]: an overview of the interaction of the SQLdb database components
566	+	- [[SqlDBHowto]]: information about using the SQLdb package
567	+	- [[Working With TSQLQuery]]: information about TSQLQuery
568	+
569	+	---
570	+	From the Free Pascal wiki, page "SQLdb Tutorial2", as it stood on 2024-03-29 after a change by Ariben, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

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