DELPHI exception calls EAccess Violation - delphi

Question

There was a question similar to this however the user was using something way more advanced so I was quite confused.
This is the procedure the exception flares up. Specifically on the ADOCon.connected line. I am using the dbgo stuff and Microsoft access for my database.
The exception I am getting is: EAcessViolation. I'm wondering what mistake I've made to cause it and how to solve it. I have run the procedure on both with a pre-existing database and a new one. When there is a pre-existing database the exception is one the 19th line and without it is on the 14th line. As a user has mentioned, I have read the documentation however I am still confused on how to solve the error. The error is definitely here as this is the first piece of access I call.
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs,DB, ADODB,ComObj;
type
TForm1 = class(TForm)
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
var
ADOCom:TADOcommand;
ADOCon:TADOConnection;
ADOQ:TADOQuery;
nameDB:string;
db:OLEVariant;
begin
namedb:='Brill.accdb';
if not fileexists(namedb) then
begin
db:=createOLEObject('ADOX.Catalog');
db.create('Provider=Microsoft.ACE.OLEDB.12.0;Data Source='+nameDB+';');
db:=null;
ADOCon.connectionstring:='Provider=Microsoft.ACE.OLEDB.12.0;Data Source='+
nameDB+';';
ADOCon.connected:=True;
ADOCon.loginprompt:=False;
end
else
ADOCon.connectionstring:='Provider=Microsoft.ACE.OLEDB.12.0;Data Source='+
nameDB+';';
end.

Answer 1

Your code is riddled with errors.
When you declare variables of a particular class type in your code, you're responsible for creating an instance of that class and assigning it to the variable before using it, and cleaning up when you're finished with it.
var
ADOCon: TAdoConnection;
ADOCom:TADOcommand;
ADOQ:TADOQuery;
begin
ADOCon := TADOConnection.Create(nil);
try
// Set up connection properties here
ADOQ := TADOQuery.Create(nil);
try
// Set up ADOQ properties and use query here
finally
ADOQ.Free;
end;
finally
ADOCon.Free;
end;
end;
Also, your use of the db: OleVariant (and all code related to it) is doing absolutely nothing. You get an instance, assign properties to that instance, and then throw it away, which means you can just delete that variable and the three lines of code related to it entirely; they serve zero purpose.
Of course, the better solution than any of the above is to add a TDataModule to your form, drop a TADOConnection and TADOQuery on it, set the properties in the Object Inspector or the OnCreate of the datamodule. You can then move that datamodule into the list of available forms, move it up to be created before your main form, and have access from anywhere in your app that uses that datamodule, and the datamodule will free everything properly when you exit your application. It also separates all of the database code from your user interface, cleaning up your code considerably.