麻烦sqlite

Question

我使用sqlite数据库开发应用程序，我需要从表中获取单行。我试过这个：

-(void)getRowFromTableNamed:(NSString *)tableName 
                   whichRow:(NSString *)row
{
    NSString *qsql = [NSString stringWithFormat:
                      @"SELECT %@ FROM %@", 
                      row, tableName];

    sqlite3_stmt *statement;
    if (sqlite3_prepare_v2(db, [qsql UTF8String], -1, &statement, nil) == SQLITE_OK) {
        if (sqlite3_step(statement) == SQLITE_OK) {
            char *field = (char *) sqlite3_column_text(statement, 0);
            NSString *fieldStr = [[NSString alloc] initWithUTF8String:field];
            self.dataString = fieldStr;
            [fieldStr release];
        } 
        sqlite3_finalize(statement);
    }
}

但它不起作用。所有其他方法都很完美。有人可以帮忙吗？

是的，我删除分号和单引号的事实并没有解决任何问题。是的，它在sqlite3_prepare_v2上失败了。

Answer 1

我最近和SQLite合作过，所以这只是我的经验猜测... 在SELECT查询中，删除分号。

"SELECT %@ FROM '%@'"

Answer 2

为什么要首先动态访问表名？我建议使用更安全的方法，并使用带参数的预准备语句，并将响应转换为模型对象，如下所示：

- (NSMutableArray *) getWidgets
{
    NSMutableArray *widgets = [[NSMutableArray alloc] init];

    sqlite3 *db;

    @try
    {
        NSFileManager *fileMgr = [NSFileManager defaultManager];
        NSString *dbPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"widgetDb.sqlite"];
        BOOL success = [fileMgr fileExistsAtPath:dbPath];

        if(!success)
            NSLog(@"Cannot locate database file '%@'.", dbPath);

        if(sqlite3_open([dbPath UTF8String], &db) != SQLITE_OK)
            NSLog(@"An error has occured.");

        const char *sql = "SELECT id, name, description FROM widgets";
        sqlite3_stmt *sqlStatement;

        if(sqlite3_prepare_v2(db, sql, -1, &sqlStatement, NULL) != SQLITE_OK)
            NSLog(@"Problem with prepare statement");

        Widget *widget;

        while (sqlite3_step(sqlStatement)==SQLITE_ROW)
        {
            widget = [[Widget alloc]init];

            widget.id = [NSNumber numberWithInt: (int)sqlite3_column_int(sqlStatement, 0)];
            widget.name = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, 1)];
            widget.description = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStatement, 2)];

            [widgets addObject:widget];
        }
    }
    @catch (NSException *exception)
    {
        NSLog(@"An exception occured: %@", [exception reason]);
    }
    @finally
    {
        return widgets;
    }
}