Mega Code Archive
How do I make a component to interact with a database table
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Title: How do I make a component to interact with a database table?
(Updated with new properties and better description)
The component below demonstrates the basics of how to wrap a component around a database table, creating a generic control over the table's contents. Type TCustomUsers has all the necessary functionality to interact with the data in a User table, without the end user having to know how to access the database. One property specifies the Connection String to the database. Each field in the database is mapped to a corresponding property in the component. Standard user properties such as Database ID, User Name, First Name, Last Name, Nick Name, Password, Etc. are linked through the properties in the options (TUserTableOptions). Therefore, it can be customized to interact with any database.
Note: Change the properties in 'Options' for TCustomUsers Component according to your user table in your database. Set the ConnectionString to your database. When you want to retrieve data from the component, call the procedure 'TCustomUsers.Refresh'.
Delphi 7 Unit: UserWrap
Types: TCustomUsers, TCustomUser, TUserTableOptions
Component: TCustomUsers
CODE
unit UserWrap;
interface
uses
Variants, Classes, DB, ADODB, SysUtils, Controls, Graphics, Forms, Windows;
type
TCustomUsers = class;
TCustomUser = class;
TUserTableOptions = class;
//Represents User Table Options
TUserTableOptions = class(TPersistent)
private
fUserTable: String; //Database Table where User Data is Stored
fIDField: String; //ID Field
fUserNameField: String; //User Name Field
fPasswordField: String; //Password Field
fFirstNameField: String; //First Name Field
fMiddleNameField: String; //Middle Name Field
fLastNameField: String; //Last Name Field
fNickNameField: String; //Nick Name Field
published
property UserTable: String read fUserTable write fUserTable;
property IDField: String read fIDField write fIDField;
property UserNameField: String read fUserNameField write fUserNameField;
property PasswordField: String read fPasswordField write fPasswordField;
property FirstNameField: String read fFirstNameField write fFirstNameField;
property MiddleNameField: String read fMiddleNameField write fMiddleNameField;
property LastNameField: String read fLastNameField write fLastNameField;
property NickNameField: String read fNickNameField write fNickNameField;
end;
//Represents an individual user
TCustomUser = class(TObject)
private
fConnectionString: String;
fID: Integer;
fUserName: String;
fPassword: String;
fFirstName: String;
fMiddleName: String;
fLastName: String;
fNickName: String;
fOwner: TCustomUsers;
function GetOptions: TUserTableOptions;
function GetID: Integer;
function GetUserName: String;
function GetFirstName: String;
function GetLastName: String;
procedure SetUserName(Value: String);
procedure SetFirstName(Value: String);
procedure SetLastName(Value: String);
function GetMiddleName: String;
function GetNickName: String;
function GetPassword: String;
procedure SetMiddleName(Value: String);
procedure SetNickName(Value: String);
procedure SetPassword(Value: String);
function ReadString(Field: String): String;
function ReadInteger(Field: String): Integer;
function SaveString(Field: String; Value: String): Bool;
function SaveInteger(Field: String; Value: Integer): Bool;
public
constructor Create(AOwner: TCustomUsers);
destructor Destroy; override;
published
property ConnectionString: String read fConnectionString write fConnectionString;
property ID: Integer read GetID; //No setting function because ID shall remain the same
property UserName: String read GetUserName write SetUserName;
property Password: String read GetPassword write SetPassword;
property FirstName: String read GetFirstName write SetFirstName;
property MiddleName: String read GetMiddleName write SetMiddleName;
property LastName: String read GetLastName write SetLastName;
property NickName: String read GetNickName write SetNickName;
property Options: TUserTableOptions read GetOptions;
end;
//Represents a set of users (TCustomUser)
TCustomUsers = class(TComponent)
private
fUserList: TStringList;
fConnectionString: String;
fOptions: TUserTableOptions;
function GetUser(Index: Integer): TCustomUser;
procedure SetConnectionString(Value: String);
function GetCount: Integer;
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
procedure Refresh;
property Count: Integer read GetCount;
property Users[Index: Integer]: TCustomUser read GetUser;
published
property ConnectionString: String read fConnectionString write SetConnectionString;
property Options: TUserTableOptions read fOptions write fOptions;
end;
procedure Register;
implementation
procedure Register;
begin
RegisterComponents('JD Custom', [TCustomUsers]);
end;
function TCustomUser.GetID: Integer;
begin
Self.fID:= Self.ReadInteger(Options.IDField);
Result:= Self.fID;
end;
function TCustomUser.GetUserName: String;
begin
Self.fUserName:= Self.ReadString(Options.UserNameField);
Result:= Self.fUserName;
end;
function TCustomUser.GetFirstName: String;
begin
Self.fFirstName:= Self.ReadString(Options.FirstNameField);
Result:= Self.fFirstName;
end;
function TCustomUser.GetLastName: String;
begin
Self.fLastName:= Self.ReadString(Options.LastNameField);
Result:= Self.fLastName;
end;
function TCustomUser.GetMiddleName: String;
begin
Self.fMiddleName:= Self.ReadString(Options.MiddleNameField);
Result:= Self.fMiddleName;
end;
function TCustomUser.GetNickName: String;
begin
Self.fNickName:= Self.ReadString(Options.NickNameField);
Result:= Self.fNickName;
end;
function TCustomUser.GetPassword: String;
begin
Self.fPassword:= Self.ReadString(Options.PasswordField);
Result:= Self.fPassword;
end;
procedure TCustomUser.SetMiddleName(Value: String);
begin
if Self.SaveString(Options.MiddleNameField, Value) then
Self.fMiddleName:= Value;
end;
procedure TCustomUser.SetNickName(Value: String);
begin
if Self.SaveString(Options.NickNameField, Value) then
Self.fNickName:= Value;
end;
procedure TCustomUser.SetPassword(Value: String);
begin
if Self.SaveString(Options.PasswordField, Value) then
Self.fPassword:= Value;
end;
procedure TCustomUser.SetUserName(Value: String);
begin
if Self.SaveString(Options.UserNameField, Value) then
Self.fUserName:= Value;
end;
procedure TCustomUser.SetFirstName(Value: String);
begin
if Self.SaveString(Options.FirstNameField, Value) then
Self.fFirstName:= Value;
end;
procedure TCustomUser.SetLastName(Value: String);
begin
if Self.SaveString(Options.LastNameField, Value) then
Self.fLastName:= Value;
end;
constructor TCustomUser.Create(AOwner: TCustomUsers);
begin
Self.fOwner:= AOwner;
end;
destructor TCustomUser.Destroy;
begin
inherited Destroy;
end;
function TCustomUser.ReadString(Field: String): String;
var
Q: TADOQuery;
begin
Result:= '';
Q:= TADOQuery.Create(nil);
try
Q.ConnectionString:= Self.fConnectionString;
Q.SQL.Text:= 'select '+Field+' from ['+Options.UserTable+'] where ['+
Options.IDField+'] = '+IntToStr(Self.fID);
Q.Open;
if not Q.IsEmpty then begin
Q.First;
Result:= Q.FieldByName(Field).AsString;
end;
Q.Close;
finally
if assigned(Q) then begin
if Q.Active then Q.Close;
Q.Free;
end;
end;
end;
function TCustomUser.ReadInteger(Field: String): Integer;
var
Q: TADOQuery;
begin
Result:= 0;
Q:= TADOQuery.Create(nil);
try
Q.ConnectionString:= Self.fConnectionString;
Q.SQL.Text:= 'select '+Field+' from ['+Options.UserTable+'] where ['+
Options.IDField+'] = '+IntToStr(Self.fID);
Q.Open;
if not Q.IsEmpty then begin
Q.First;
Result:= Q.FieldByName(Field).AsInteger;
end;
Q.Close;
finally
if assigned(Q) then begin
if Q.Active then Q.Close;
Q.Free;
end;
end;
end;
function TCustomUser.SaveString(Field: String; Value: String): Bool;
var
Q: TADOQuery;
begin
Result:= False;
Q:= TADOQuery.Create(nil);
try
Q.ConnectionString:= Self.fConnectionString;
Q.SQL.Text:= 'select '+Field+' from ['+Options.UserTable+'] where ['+
Options.IDField+'] = '+IntToStr(Self.fID);
Q.Open;
if not Q.IsEmpty then begin
Q.First;
try
Q.Edit;
Q[Field]:= Value;
Q.Post;
Result:= True;
except
on e: exception do begin
Result:= False;
end;
end;
end;
Q.Close;
finally
if assigned(Q) then begin
if Q.Active then Q.Close;
Q.Free;
end;
end;
end;
function TCustomUser.SaveInteger(Field: String; Value: Integer): Bool;
var
Q: TADOQuery;
begin
Result:= False;
Q:= TADOQuery.Create(nil);
try
Q.ConnectionString:= Self.fConnectionString;
Q.SQL.Text:= 'select '+Field+' from ['+Options.UserTable+'] where ['+
Options.IDField+'] = '+IntToStr(Self.fID);
Q.Open;
if not Q.IsEmpty then begin
Q.First;
try
Q.Edit;
Q[Field]:= Value;
Q.Post;
Result:= True;
except
on e: exception do begin
Result:= False;
end;
end;
end;
Q.Close;
finally
if assigned(Q) then begin
if Q.Active then Q.Close;
Q.Free;
end;
end;
end;
function TCustomUser.GetOptions: TUserTableOptions;
begin
Result:= Self.fOwner.Options;
end;
function TCustomUsers.GetUser(Index: Integer): TCustomUser;
begin
if (Index = 0) and (Index Delphi 7 Unit: uMain
Form: Form1
Controls: ListBox1: TListBox, CustomUsers1: TCustomUsers
Methods: Form1.FormCreate
CODE
unit uMain;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, UserWrap, StdCtrls;
type
TForm1 = class(TForm)
CustomUsers1: TCustomUsers;
ListBox1: TListBox;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
var
X: Integer;
U: TCustomUser;
Str: String;
begin
CustomUsers1.Refresh;
ListBox1.Clear;
for X:= 0 to CustomUsers1.Count - 1 do begin
U:= CustomUsers1.Users[X];
Str:= U.UserName + ' - ' + U.FirstName + ' ' + U.MiddleName + ' ' + U.LastName;
Str:= Str + ' | '+ U.NickName;
ListBox1.Items.Append(Str);
end;
end;
end.
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