如何使用FMDB在sqlite中以编程方式创建表

Question

我是项目中目标c的初学者我正在使用SQLite，在这里我使用FMDB以编程方式创建表格，但是当运行项目时，它显示异常，如

＆＃34; [NSFileManager copyItemAtPath：toPath：error：]：源路径为nil＆＃34;

请帮帮我一个

这是我的代码

NSFileManager *fileManager = [NSFileManager defaultManager];
    NSURL *dbUrl = [fileManager URLForDirectory:NSDocumentDirectory
                                       inDomain:NSUserDomainMask appropriateForURL:nil
                                         create:NO error:nil];

    dbUrl = [dbUrl URLByAppendingPathComponent:@"studentdb.sqlite"];
    FMDatabase * db = [FMDatabase databaseWithPath:dbUrl.absoluteString];

    if([db open]){

        NSString *dbCarTableCreate = @"CREATE TABLE IF NOT EXISTS studentInfo1(rollnum integer primary key autoincrement,name text,age text)";

        if([db executeUpdate:dbCarTableCreate]){

            NSLog(@"Table create success");
        }

        else{

            NSLog(@"%@",db.lastError);
            NSLog(@"%@",db.lastErrorMessage);
        }
    }

Answer 1

现在路径不是零，如果您尝试以下答案

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory , NSUserDomainMask, YES);
NSString *documentsDir = [paths objectAtIndex:0];
NSString *documentsDirectory = [documentsDir stringByAppendingPathComponent:@"studentdb.sqlite"];
if (![[NSFileManager defaultManager] fileExistsAtPath:documentsDirectory])
{
    NSString *backupDbPath = [[NSBundle mainBundle] pathForResource:@"studentdb" ofType:@"sqlite"];

    NSLog(@"Test backup path is - %@",backupDbPath);
    if (backupDbPath == nil)
    {
        NSLog(@"Database path is nil");
    }
    else
    {
        BOOL copiedBackupDb = [[NSFileManager defaultManager] copyItemAtPath:backupDbPath toPath:documentsDirectory error:nil];
        if (!copiedBackupDb){
            NSLog(@"Copying database failed");
        }
    }
}

输出

  

测试备份路径是 -   /Users/name/Library/Developer/CoreSimulator/Devices/35CDFFA0-36A1-499D-8D17-7EF356F1151E/data/Containers/Bundle/Application/DEA0343A-05C8-4411-BF92-4000918E492A/DataBaseDemo.app/studentdb.sqlite