要从NSBundle获取预先填充的数据库的位置：

let databasePath = NSBundle.mainBundle().URLForResource("databaseName",withExtension:"sqlite3");

使用NSFileManager获取文档目录的URL：

//Should have an error pointed in case there is an error.
let documentsDirectory = NSFileManager.defaultManager().URLForDirectory(NSSearchPathDirectory.DocumentDirectory,inDomain:NSSearchPathDomainMask.UserDomainMask,url:nil,shouldCreate:false,error:nil);

最后复制文件：

if let source = databasePath,destination = documentsDirectory
{
   destination = destination.URLByAppendingPathComponent("database.sqlite3")
   var result = NSFileManager.defaultManager().copyItemAtURL(source,toURL:destination,error:nil)
 
   //Should have an error pointer,check that the result is true. If not check error.
}