TAdoConnectionEx - Custom Delphi Component With Source

Preventing Design Time Database Connection

The article An Error at Run-Time due to the Database Connection Left Open at Design-Time explains why sometimes live database data at design-time can cause problems at run time.

In short, when the application is started, if the Connected property is left to "True", at design-time, the application will try to connect to the database using the "hard" coded ConnectionString property!

TAdoConnectionEx

Here's the full source code (yes, it is that small) to a custom TADOConnection derived component.

The TAdoConnectionEx is an enhanced ADO connection component that prevents design-time database connections from being used at run-time unless explcitily allowed via the AllowStreamConnected property.

unit ADOConnectionEx;

interface

uses ADODB, Classes;

{
  Enhanced ADO connection component that prevents design-time database connections
  from being used at run-time unless explcitily allowed via the AllowStreamConnected
  property.

  Author: Larry Hengen
}

type
  TADOConnectionEx = class(TADOConnection)
  private
    fAllowStreamConnected: boolean;
  protected
    procedure SetConnected(Value : boolean) ; override;
  published
    property AllowStreamConnected : boolean read fAllowStreamConnected write fAllowStreamConnected;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('delphi.about.com', [TADOConnectionEx]) ;
end;


procedure TADOConnectionEx.SetConnected(Value : boolean) ;
begin
  //if we are not to allow a connection to be established
  //when reading in the form, then
  //toggle it to false when Reading
  if not(FAllowStreamConnected) and (Value) and (csReading in ComponentState) then
    inherited SetConnected(False)
  else
    inherited SetConnected(Value) ;
end;

end.

Basically, the SetConnected method - a protected method that gets called when the public Open method is used.

Installing into the Component palette

The TADoConnectionEx source code above, should be saved in a single unit file (ADOConnectionEx.pas). You'll need to add the component into an existing package. Here's How to Install Custom Component in Delphi (into Existing Package).