On Mon, Jul 14, 2003 at 02:26:28PM +0200, Michael Van Canneyt wrote:
>
>
> On Mon, 14 Jul 2003, James Mills wrote:
>
> > On Mon, Jul 14, 2003 at 09:59:17AM +0200, Michael Van Canneyt wrote:
> > >
> > >
> > > On Mon, 14 Jul 2003, James Mills wrote:
> > >
> > > > Hi,
> > > >
> > > > This is a very weird behaviour I've found of either SQLite, or the Unit.
> > > > I'm not sure... I have been discussing this same problem on the SQLite
> > > > mailing list but without success there, so perhaps someone here might
> > > > know...
> > > >
> > > > I have attached a test database, which contains 1 database entry, null
> > > > strings are inserted using NULL... Check the database schema yourself.
> > > >
> > > > The problem therein lies in the fact that test3.pas returns "" for the
> > > > query: SELECT channelNotice FROM channels WHERE channel LIKE '#ProLogiTech';
> > > > It should return a null string as it does in test2.pas and in the sqlite
> > > > shell program.
> > >
> > > The problem is that an implicity conversion from Nil to empty string is
> > > done. You cannot solve this as long as stringlists are used to contain
> > > the data. (ok, you could set 'Null' as the string, but that is sloppy)
> >
> > "is done." in what ? The SQLite library or TStringList ?
>
> sqlite.
But you said "You cannot solve this as long as stringlists are used to
contain the data." This made me think it was a behaviour of TStringList
... If it truely is a behaviour of SQLite, I'll get them to change it.
>
> >
> > >
> > > You'd need to have (as a minimum) an array of TField records:
> > > TField = Record
> > > IsNull : Boolean;
> > > Value : String;
> > > end;
> > >
> > > But this will require major changes, so I suggest trying to find or
> > > implement a TDataset descendent for SQLIte, this will solve most of
> > > your problems at once.
> >
> > How major would the changes be ? Otherwise I'll try and search for a
> > TDataset descendent ? Couldn't I write a descendent myself ? (I've kinda
> > of done something similar in creating a TDatabase descendant..., but it
> > doesn't solve my problem)
>
> Implementing a TDataset descendent is not easy, it'll take you at least
> a week (conservative estimate).
Why is this a hard thing to do ? Give me some ideas here, you might be
conservative, but I don't muck around :)
I'll attach my dbclass.pas a tiny desendant I wrote to simplify using
queries (it's centered around making queries simpler)...
cheers
James
>
> Michael.
>
>
> _______________________________________________
> fpc-pascal maillist - [EMAIL PROTECTED]
> http://lists.freepascal.org/mailman/listinfo/fpc-pascal
--
-
- James Mills
Zero Defect Software Engineers Group - ZDSEG
unit dbClass;
interface
uses
cMem, SQLite, SQLiteDB, Strings, Classes, Functions;
type
TDatabase = class(TObject)
constructor Create;
destructor Destroy; override;
protected
SQL: TSQLite;
X: Integer;
Y: Integer;
S: TStringList;
function simpleQuery(query: String): String;
function complexQuery(query: String): TStringList;
function multiQuery(query: String): TStringList;
public
end;
implementation
constructor TDatabase.Create;
begin
end;
destructor TDatabase.Destroy;
begin
inherited Destroy;
if NOT (SQL = nil) then
begin
SQL.Free;
end;
end;
function TDatabase.simpleQuery(query: String): String;
var
tmp: String;
begin
tmp := query;
replace('''''', 'NULL', tmp);
writeLn('simpleQuery - ', tmp);
if NOT (SQL = nil) then
begin
SQL.Query(tmp, nil);
if (SQL.List_Field.count > 0) then
begin
S := TStringList(SQL.List_Field.items[0]);
simpleQuery := S.Strings[0];
end
else
begin
simpleQuery := '';
end;
end;
end;
function TDatabase.complexQuery(query: String): TStringList;
var
tmp: String;
begin
tmp := query;
replace('''''', 'NULL', tmp);
writeLn('complexQuery - ', tmp);
if NOT (SQL = nil) then
begin
SQL.Query(tmp, nil);
if (SQL.List_Field.count > 0) then
begin
complexQuery := TStringList(SQL.List_Field.items[0]);
end
else
begin
complexQuery := TStringList.Create;
end;
end;
end;
function TDatabase.multiQuery(query: String): TStringList;
var
temp: String;
tmp: String;
I: Integer;
J: Integer;
strs: TStringList;
begin
temp := query;
replace('''''', 'NULL', temp);
writeLn('multiQuery - ', temp);
if NOT (SQL = nil) then
begin
SQL.Query(temp, nil);
if (SQL.List_Field.count > 0) then
begin
strs := TStringList.Create;
for I := 0 to (SQL.List_Field.Count - 1) do
begin
tmp := '';
for J := 0 to (TStringList(SQL.List_Field.Items[I]).Count - 1) do
begin
tmp := tmp + TStringList(SQL.List_Field.Items[I]).Strings[J] + ' ';
end;
tmp := copy(tmp, 1, (length(tmp) - 1));
strs.add(tmp);
end;
for I := 0 to (strs.Count - 1) do
begin
writeLn(I, ' - ', strs.Strings[I]);
end;
multiQuery := strs;
end
else
begin
multiQuery := TStringList.Create;
end;
end;
end;
end.
