[yunqa.de] Re: SQLite metadata
- From: Delphi Inspiration <delphi@xxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Wed, 03 Jun 2009 17:42:01 +0200
At 12:50 01.06.2009, Radovan Antloga wrote:
>I did add also that this can't be reproduced with sqlite3.exe.
I investigated further and found that sqlite3.exe encounters the same problem
but works around it by calling sqlite3_prepare() a 2nd time after
SQLITE_SCHEMA. I have appended http://www.sqlite.org/cvstrac/tktview?tn=3890
accordingly.
For DISQLite3 and Delphi, a similar workaround might look like this:
Retries := 0;
repeat
Inc(Retries);
e := sqlite3_prepare(Db2, 'select a from t', -1, @Stmt, nil);
until (e <> SQLITE_SCHEMA) or (Retries > 1);
The full source code is in the attach.
Ralf { Visit the DISQLite3 Internet site for latest information and updates:
http://www.yunqa.de/delphi/
Copyright (c) 2009 Ralf Junker, The Delphi Inspiration <delphi@xxxxxxxx>
------------------------------------------------------------------------------ }
program DISQLite3_Multiple_Connections;
{$APPTYPE CONSOLE}
{$I DI.inc}
{$I DISQLite3.inc}
uses
{$IFDEF FastMM}FastMM4, {$ENDIF}Windows, DISQLite3Api;
//------------------------------------------------------------------------------
procedure r(const DB: sqlite3; const SQL: AnsiString);
var
Stmt: sqlite3_stmt;
begin
sqlite3_check(sqlite3_prepare(DB, PAnsiChar(SQL), -1, @Stmt, nil), DB);
while sqlite3_check(sqlite3_step(Stmt), DB) = SQLITE_ROW do
WriteLn(sqlite3_column_str(Stmt, 0));
sqlite3_check(sqlite3_finalize(Stmt), DB);
end;
var
e, Retries: Integer;
Db1, Db2: sqlite3;
Stmt: sqlite3_stmt;
begin
DeleteFile('test.db3');
{ Open 2 database connections. }
sqlite3_check(sqlite3_open('test.db3', @Db1));
sqlite3_check(sqlite3_open('test.db3', @Db2));
sqlite3_exec_fast(Db2, 'pragma synchronous=full');
{ Create table in connection 1. }
sqlite3_exec_fast(Db1, 'create table t(a)');
sqlite3_exec_fast(Db1, 'insert into t values (1)');
sqlite3_exec_fast(Db1, 'insert into t values (2)');
{ Use connection 2 to read from table created in connection 1.
Retry to prepare the statement if the initial call to sqlite3_prepare() or
sqlite3_prepare_v2() returns SQLITE_SCHEMA. }
Retries := 0;
repeat
Inc(Retries);
e := sqlite3_prepare(Db2, 'select a from t', -1, @Stmt, nil);
until (e <> SQLITE_SCHEMA) or (Retries > 1);
sqlite3_check(e, Db2);
while sqlite3_check(sqlite3_step(Stmt), Db2) = SQLITE_ROW do
WriteLn(sqlite3_column_str(Stmt, 0));
sqlite3_check(sqlite3_finalize(Stmt), Db2);
{ Cleanup. }
sqlite3_check(sqlite3_close(Db2), Db2);
sqlite3_check(sqlite3_close(Db1), Db1);
sqlite3_shutdown;
WriteLn;
WriteLn('Done - Press ENTER to Exit');
ReadLn;
end.
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