[yunqa.de] Re: TDISQLite3UniDirQuery record count [this does work]
- From: Delphi Inspiration <delphi@xxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Tue, 23 Mar 2010 10:52:13 +0100
At 18:15 22.03.2010, Todd Cary wrote:
>Attached is a test application that contains enough of the application code so
>that it is similar to my actual application. When the Test button is pressed,
>a check is done to see if a table exists. The DISQLiteDatabase is closed
>before the check is done to make sure it is not in use.
There are two problems in your code. In a nutshell, it looks like this:
01 var
02 DB: TDISQLite3Database;
03 begin
04 DB := TDISQLite3Database.Create(nil);
05 DB.DatabaseName := 'test.db3';
06 try
07 DB.Open;
08 except
09 DB.CreateDatabase;
10 end;
11 DB.Close; // For testing
12
13 Sqlite3_Exists_Table(Pointer(DB), 'Cards_Tmp');
1. sqlite3_exists_table expectes a sqlite3_ptr handle, but you are passing to
it an instance of TDISQLite3Database (line 13). Because the latter is rejected
by the compiler, you are casting it to Pointer. It now compiles, but does not
make sense and does not work. The solution is to call sqlite3_exists_table
(DB.Handle). Read the DISQLite3 version 2.2.0 change log entry for for the
recently enforced compiler type checking.
2. In line 11 you are closing the database. Database operations do not work on
closed databases. The solution is to keep the database open until all
operations are finished.
The following piece of code corrects the above errors:
var
DB: TDISQLite3Database;
begin
DB := TDISQLite3Database.Create(nil);
try
DB.DatabaseName := 'test.db3';
try
DB.Open;
except
DB.CreateDatabase;
end;
Sqlite3_Exists_Table(DB.Handle, 'Cards_Tmp');
DB.Close;
finally
DB.Free;
end;
end;
Ralf
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