SQLdb Tutorial3
- work in progress; to do: finish me ***
Overview
In this tutorial, you will learn to make your application suitable for multiple databases. You will see how to get database data in normal controls (instead of database controls), and how to execute parametrized queries.
Multi database support
Using any database and a login form.
advantages: - user/programmer can dynamically use any sqldb t*connection, so he can choose between dbs
disadvantages - more complicated SQL will likely need to still be adapted - you can't use T*connection specific properties (like TIBConnection.Dialect to set Firebird dialect). - complicates code some
to do: Expand this code to also show a form if needed for user input and do arguments handling from command line. Also perhaps create a non-gui version to do: get ludob's version from the forum, IIRC that was a form based thingy.
unit dbconfig;
{ Small unit that retrieves connection settings for your database
Copyright (c) 2012 Reinier Olislagers
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to
deal in the Software without restriction, including without limitation the
rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
sell copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
IN THE SOFTWARE.
}
//todo: add command line support (--dbtype=, --db=, --dbhost=, dbuser=, dbpass=, dbcharset=
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, IniFiles;
type
{ TDBConnectionConfig }
TDBConnectionConfig = class(TObject)
private
FDBCharset: string;
FDBType: string;
FDBHost: string;
FDBPath: string;
FDBUser: string;
FDBPassword: string;
FSettingsFileIsRead: boolean; //indicates if we read in settings file
FSettingsFile: string;
function GetDBCharset: string;
function GetDBHost: string;
function GetDBPassword: string;
function GetDBPath: string;
function GetDBType: string;
function GetDBUser: string;
function GetDefaultSettingsFile:string;
procedure ReadINIFile;
procedure SetDBType(AValue: string);
procedure SetSettingsFile(AValue: string);
public
property DBCharset: string read GetDBCharset write FDBCharset; //Character set used for database (e.g. UTF8)
property DBHost: string read GetDBHost write FDBHost; //Database host/server (name or IP address). Leave empty for embedded
property DBPath: string read GetDBPath write FDBPath; //Path/database name
property DBUser: string read GetDBUser write FDBUser; //User name needed for database (e.g. sa, SYSDBA)
property DBPassword: string read GetDBPassword write FDBPassword; //Password needed for user name
property DBType: string read GetDBType write SetDBType; //Type of database connection, e.g. Firebird, Oracle
property SettingsFile: string read FSettingsFile write SetSettingsFile; //ini file to read settings from. If empty defaults to <programname>.ini
constructor Create;
constructor Create(DefaultType:string; DefaultHost:string=''; DefaultPath:string='data.fdb';
DefaultUser:string='SYSDBA'; DefaultPassword:string='masterkey'; DefaultCharSet:string='UTF8');
destructor Destroy; override;
end;
implementation
{ TDBConnectionConfig }
function TDBConnectionConfig.GetDBHost: string;
begin
if not(FSettingsFileIsRead) then ReadINIFile;
result:=FDBHost;
end;
function TDBConnectionConfig.GetDBCharset: string;
begin
if not(FSettingsFileIsRead) then ReadINIFile;
result:=FDBCharset;
end;
function TDBConnectionConfig.GetDBPassword: string;
begin
if not(FSettingsFileIsRead) then ReadINIFile;
result:=FDBPassword;
end;
function TDBConnectionConfig.GetDBPath: string;
begin
if not(FSettingsFileIsRead) then ReadINIFile;
result:=FDBPath;
end;
function TDBConnectionConfig.GetDBType: string;
begin
if not(FSettingsFileIsRead) then ReadINIFile;
result:=FDBType;
end;
function TDBConnectionConfig.GetDBUser: string;
begin
if not(FSettingsFileIsRead) then ReadINIFile;
result:=FDBUser;
end;
function TDBConnectionConfig.GetDefaultSettingsFile:string;
begin
result:=ChangeFileExt(ParamStr(0), '.ini');
end;
procedure TDBConnectionConfig.SetSettingsFile(AValue: string);
begin
// If empty value given, use the program name
if AValue='' then AValue:=GetDefaultSettingsFile;
if FSettingsFile=AValue then Exit;
FSettingsFile:=AValue;
// Read from file if present
ReadINIFile;
end;
procedure TDBConnectionConfig.SetDBType(AValue: string);
begin
if FDBType=AValue then Exit;
case UpperCase(AValue) of
'FIREBIRD': FDBType:='Firebird';
'POSTGRES', 'POSTGRESQL': FDBType:='PostgreSQL';
'SQLITE','SQLITE3': FDBType:='SQLite';
else FDBType:=AValue;
end;
end;
procedure TDBConnectionConfig.ReadINIFile;
var
INI: TIniFile;
begin
if FileExists(FSettingsFile) then
begin
INI := TINIFile.Create(FSettingsFile);
try
FDBType := INI.ReadString('Database', 'DatabaseType', FDBType); //Default to Firebird
FDBHost := INI.ReadString('Database', 'Host', FDBHost);
FDBPath := INI.ReadString('Database', 'Database', FDBPath);
FDBUser := INI.ReadString('Database', 'User', 'SYSDBA');
FDBPassword := INI.ReadString('Database', 'Password', 'masterkey');
FSettingsFileIsRead:=true;
finally
INI.Free;
end;
end;
end;
constructor TDBConnectionConfig.Create;
begin
inherited Create;
// Defaults
FSettingsFile:=GetDefaultSettingsFile;
FSettingsFileIsRead:=false;
FDBType := 'Firebird';
FDBHost := ''; //embedded
FDBPath := 'data.fdb';
FDBUser := 'SYSDBA';
FDBPassword := 'masterkey';
end;
constructor TDBConnectionConfig.Create(DefaultType:string; DefaultHost:string=''; DefaultPath:string='data.fdb';
DefaultUser:string='SYSDBA'; DefaultPassword:string='masterkey'; DefaultCharSet:string='UTF8');
begin
create;
FDBCharset:=DefaultCharset;
FDBHost:=DefaultHost;
FDBPassword:=DefaultPassword;
FDBPath:=DefaultPath;
FDBType:=DefaultType;
FDBUser:=DefaultUser;
end;
destructor TDBConnectionConfig.Destroy;
begin
inherited Destroy;
end;
end.
add section on creating dbs here, handy for embedded (sqlite, firebird); also do firebird c/s to contrast
Getting database data into normal controls
Refer to the SQLdb Tutorial Database setup page (to be created) with instructions on how to set up employee database with the employees tables.
Aggregate query: max and min salary and corresponding employee (select ... from salary...) Get results in stringgrid.
Adapting SQL for various databases
use standard deviation for salary select ... from employees... Hopefully postgresql has a built in stddev function Indicate this may not work on all dbs Show result in labels or tedits
Executing queries & getting data out of normal controls into the database
Previously, we have seen how to get data out of the databse using queries, and how to let SQLDB update the databse with db controls. You can also execute any SQL you want on the database via code, and we're going to use that to show how to use normal non db controls to get data into the database.
This allows you to use controls that have no db aware equivalent such as sliders or custom controls to enter data into the database, at the expense of a bit more coding. INSERT INTO ... EMPLOYEE... or UPDATE EMPLOYEE... or MERGE... Think about this one...
Code
dbconfig.pas
<syntaxhiglight> unit dbconfig;
{ Small unit that retrieves connection settings for your database
Copyright (c) 2012 Reinier Olislagers
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
}
//todo: add command line support (--dbtype=, --db=, --dbhost=, dbuser=, dbpass=, dbcharset= {$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, IniFiles;
type
{ TDBConnectionConfig } TDBConnectionConfig = class(TObject) private FDBCharset: string; FDBType: string; FDBHost: string; FDBPath: string; FDBUser: string; FDBPassword: string; FSettingsFileIsRead: boolean; //indicates if we read in settings file FSettingsFile: string; function GetDBCharset: string; function GetDBHost: string; function GetDBPassword: string; function GetDBPath: string; function GetDBType: string; function GetDBUser: string; function GetDefaultSettingsFile:string; procedure ReadINIFile; procedure SetDBType(AValue: string); procedure SetSettingsFile(AValue: string); public property DBCharset: string read GetDBCharset write FDBCharset; //Character set used for database (e.g. UTF8) property DBHost: string read GetDBHost write FDBHost; //Database host/server (name or IP address). Leave empty for embedded property DBPath: string read GetDBPath write FDBPath; //Path/database name property DBUser: string read GetDBUser write FDBUser; //User name needed for database (e.g. sa, SYSDBA) property DBPassword: string read GetDBPassword write FDBPassword; //Password needed for user name property DBType: string read GetDBType write SetDBType; //Type of database connection, e.g. Firebird, Oracle property SettingsFile: string read FSettingsFile write SetSettingsFile; //ini file to read settings from. If empty defaults to <programname>.ini constructor Create; constructor Create(DefaultType:string; DefaultHost:string=; DefaultPath:string='data.fdb'; DefaultUser:string='SYSDBA'; DefaultPassword:string='masterkey'; DefaultCharSet:string='UTF8'); destructor Destroy; override; end;
implementation
{ TDBConnectionConfig }
function TDBConnectionConfig.GetDBHost: string; begin
if not(FSettingsFileIsRead) then ReadINIFile; result:=FDBHost;
end;
function TDBConnectionConfig.GetDBCharset: string; begin
if not(FSettingsFileIsRead) then ReadINIFile; result:=FDBCharset;
end;
function TDBConnectionConfig.GetDBPassword: string; begin
if not(FSettingsFileIsRead) then ReadINIFile; result:=FDBPassword;
end;
function TDBConnectionConfig.GetDBPath: string; begin
if not(FSettingsFileIsRead) then ReadINIFile; result:=FDBPath;
end;
function TDBConnectionConfig.GetDBType: string; begin
if not(FSettingsFileIsRead) then ReadINIFile; result:=FDBType;
end;
function TDBConnectionConfig.GetDBUser: string; begin
if not(FSettingsFileIsRead) then ReadINIFile; result:=FDBUser;
end;
function TDBConnectionConfig.GetDefaultSettingsFile:string; begin
result:=ChangeFileExt(ParamStr(0), '.ini');
end;
procedure TDBConnectionConfig.SetSettingsFile(AValue: string); begin
// If empty value given, use the program name if AValue= then AValue:=GetDefaultSettingsFile; if FSettingsFile=AValue then Exit; FSettingsFile:=AValue; // Read from file if present ReadINIFile;
end;
procedure TDBConnectionConfig.SetDBType(AValue: string);
begin
if FDBType=AValue then Exit; case UpperCase(AValue) of 'FIREBIRD': FDBType:='Firebird'; 'POSTGRES', 'POSTGRESQL': FDBType:='PostgreSQL'; 'SQLITE','SQLITE3': FDBType:='SQLite'; else FDBType:=AValue; end;
end;
procedure TDBConnectionConfig.ReadINIFile; var
INI: TIniFile;
begin
if FileExists(FSettingsFile) then begin INI := TINIFile.Create(FSettingsFile); try FDBType := INI.ReadString('Database', 'DatabaseType', FDBType); //Default to Firebird FDBHost := INI.ReadString('Database', 'Host', FDBHost); FDBPath := INI.ReadString('Database', 'Database', FDBPath); FDBUser := INI.ReadString('Database', 'User', 'SYSDBA'); FDBPassword := INI.ReadString('Database', 'Password', 'masterkey'); FSettingsFileIsRead:=true; finally INI.Free; end; end;
end;
constructor TDBConnectionConfig.Create; begin
inherited Create; // Defaults FSettingsFile:=GetDefaultSettingsFile; FSettingsFileIsRead:=false; FDBType := 'Firebird'; FDBHost := ; //embedded FDBPath := 'data.fdb'; FDBUser := 'SYSDBA'; FDBPassword := 'masterkey';
end;
constructor TDBConnectionConfig.Create(DefaultType:string; DefaultHost:string=; DefaultPath:string='data.fdb';
DefaultUser:string='SYSDBA'; DefaultPassword:string='masterkey'; DefaultCharSet:string='UTF8');
begin
create; FDBCharset:=DefaultCharset; FDBHost:=DefaultHost; FDBPassword:=DefaultPassword; FDBPath:=DefaultPath; FDBType:=DefaultType; FDBUser:=DefaultUser;
end;
destructor TDBConnectionConfig.Destroy; begin
inherited Destroy;
end;
end. </syntaxhighlight>
dbconfiggui.pas
<syntaxhiglight> unit dbconfiggui;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, dbconfig;
type
TConnectionTestFunction = function(ChosenConfig: TDBConnectionConfig): boolean of object; { TDBConfigForm }
TDBConfigForm = class(TForm) OKButton: TButton; CancelButton: TButton; TestButton: TButton; ConnectorType: TComboBox; Host: TEdit; Database: TEdit; Label1: TLabel; Label2: TLabel; Label3: TLabel; Label4: TLabel; Label5: TLabel; Password: TEdit; User: TEdit; procedure ConnectorTypeEditingDone(Sender: TObject); procedure DatabaseEditingDone(Sender: TObject); procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); procedure FormShow(Sender: TObject); procedure HostEditingDone(Sender: TObject); procedure PasswordEditingDone(Sender: TObject); procedure TestButtonClick(Sender: TObject); procedure UserEditingDone(Sender: TObject); private FConnectionConfig: TDBConnectionConfig; FConnectionTestFunction: TConnectionTestFunction; FSetupComplete: boolean; { private declarations } public property Config: TDBConnectionConfig read FConnectionConfig; property ConnectionTestCallback: TConnectionTestFunction write FConnectionTestFunction; { public declarations } end;
var
DBConfigForm: TDBConfigForm;
implementation
{$R *.lfm}
{ TDBConfigForm }
procedure TDBConfigForm.TestButtonClick(Sender: TObject); begin
// Call callback with settings, let it figure out if connection succeeded and // get test result back if assigned(FConnectionTestFunction) and assigned(FConnectionConfig) then if FConnectionTestFunction(FConnectionConfig) then showmessage('Connection test succeeded.') else showmessage('Connection test failed.') else showmessage('Error: connection test code has not been implemented.');
end;
procedure TDBConfigForm.UserEditingDone(Sender: TObject); begin
FConnectionConfig.DBUser:=User.Text;
end;
procedure TDBConfigForm.FormCreate(Sender: TObject); begin
FConnectionConfig:=TDBConnectionConfig.Create; FSetupComplete:=false;
end;
procedure TDBConfigForm.ConnectorTypeEditingDone(Sender: TObject); begin
FConnectionConfig.DBType:=ConnectorType.Text;
end;
procedure TDBConfigForm.DatabaseEditingDone(Sender: TObject); begin
FConnectionConfig.DBPath:=Database.Text;
end;
procedure TDBConfigForm.FormDestroy(Sender: TObject); begin
FConnectionConfig.Free;
end;
procedure TDBConfigForm.FormShow(Sender: TObject); begin
if not FSetupComplete then begin // Only do this once in form's lifetime FSetupComplete:=true; ConnectorType.Text:=FConnectionConfig.DBType; Host.Text:=FConnectionConfig.DBHost; Database.Text:=FConnectionConfig.DBPath; User.Text:=FConnectionConfig.DBUser; Password.Text:=FConnectionConfig.DBPassword; end;
end;
procedure TDBConfigForm.HostEditingDone(Sender: TObject); begin
FConnectionConfig.DBHost:=Host.Text;
end;
procedure TDBConfigForm.PasswordEditingDone(Sender: TObject); begin
FConnectionConfig.DBPassword:=Password.Text;
end;
end. </syntaxhighlight>
mainform.pas
<syntaxhiglight> unit mainform;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, dbconfiggui,dbconfig, {General db unit}sqldb, {Now we add all databases we want to support, otherwise their drivers won't be loaded} IBConnection,pqconnection,sqlite3conn;
type
{ TForm1 }
TForm1 = class(TForm) procedure FormCreate(Sender: TObject); private { private declarations } function ConnectionTest(ChosenConfig: TDBConnectionConfig): boolean; public { public declarations } end;
var
Form1: TForm1;
implementation
{$R *.lfm}
{ TForm1 }
procedure TForm1.FormCreate(Sender: TObject); var
LoginForm: TDBConfigForm;
begin
LoginForm:=TDBConfigForm.Create(self); try // The test button on dbconfiggui will link to this procedure: LoginForm.ConnectionTestCallback:=@ConnectionTest; LoginForm.ConnectorType.Clear; //remove any default connectors // Now add the dbs that you support - use the name of the *ConnectionDef.TypeName property LoginForm.ConnectorType.AddItem('Firebird', nil); LoginForm.ConnectorType.AddItem('PostGreSQL', nil); LoginForm.ConnectorType.AddItem('SQLite3', nil); //No connectiondef object yet in FPC2.6.0 case LoginForm.ShowModal of mrOK: begin //user wants to connect, so copy over db info end; mrCancel: begin ShowMessage('You canceled the database login. Application will terminate.'); Close; end; end; finally LoginForm.Free; end;
end;
function TForm1.ConnectionTest(ChosenConfig: TDBConnectionConfig): boolean; // Callback function that uses the info in dbconfiggui to test a connection // and return the result of the test to dbconfiggui var
// Generic database connector... Conn: TSQLConnector;
begin
result:=false; Conn:=TSQLConnector.Create(nil); Screen.Cursor:=crHourglass; try // ...actual connector type is determined by this property. // Make sure the ChosenConfig.DBType string matches // the connectortype. Conn.ConnectorType:=ChosenConfig.DBType; Conn.HostName:=ChosenConfig.DBHost; Conn.DatabaseName:=ChosenConfig.DBPath; Conn.UserName:=ChosenConfig.DBUser; Conn.Password:=ChosenConfig.DBPassword; try Conn.Open; if Conn.Connected=true then result:=true; except // Result is already false end; Conn.Close; finally Screen.Cursor:=crDefault; Conn.Free; end;
end;
end. </syntaxhighlight>
[Category:Databases] [Category:Tutorials] [Category:Lazarus]