SSMS可扩展性/插件 - 获取当前数据库和服务器(SSMS extensibility/addin - get current database and server)

 编辑 - 似乎我没有正确解释，人们不知道它是如何工作的。 我的错。 我会试着更好地解释它。 
 
 原因在于for命令的内部工作方式。 
 
 当到达for var in (files)行时，将检查目录以查看是否有任何文件匹配并需要处理。 
 
 然后， for命令（真正的cmd），发出一个目录查询来枚举这些文件。 此查询只返回集合中的第一个文件 。 如果有任何与for命令中的文件掩码相匹配的辅助文件，则会设置一个标志，指示调用方（cmd）有更多要处理的文件，但其余文件的列表尚未检索 。 
 
 当执行内部代码for达到迭代结束时，并且有待处理的文件被读取时，会发送一个查询以获取待处理文件列表的剩余部分，并与for文件选择相匹配。 
 
 系统使用剩余文件列表填充缓冲区。 如果此时文件列表足够短以便在缓冲区中完全播放，则查询将不会重复。 如果文件列表大小不足以放入缓冲区，则检索部分列表，并在处理检索列表中的文件时，再次发送查询以获取更多文件进行处理。 
 
 缓冲区中的文件数量取决于文件名的长度。 文件名越短，缓冲区中的文件越多，查询文件系统越少。 
 
 此行为（仅在文件查询返回存在待处理文件时才会执行（在第一个文件处理结束时检索剩余文件列表）。 当一个查询不返回该标志时，不会检索到更多文件。 
 
 例外 
 
 如果在NTFS中工作，如果文件按字母顺序大于在for命令中处理的最后一个文件，则文件仅包含在“重新查询”中。 
 
 如果FAT工作，则查询将包括所有生成的与文件选择独立匹配的新文件。 是的，它可能陷入无限循环。 （在测试中，系统缓冲区只检索一个文件名，并在每次迭代中检索）。 你可以试试 
 
break > a.txt && cmd /v:on /c "for %f in (*.txt) do break > !random!.txt"
 
 我所有的测试都是在Windows 7 64位，NTFS和FAT32分区上进行的（在USB驱动器上）。 没办法测试其他配置。 如果有人看到不同的行为，请评论。 
 
 有关更多信息，请参阅ZwQueryDirectoryFile 

EDITED - Seems i've not explained it properly and people doesn't see how it works. My fault. I'm going to try to explain it better.
 
The reason is the way the for command works internally. 
 
When the line for var in (files) is reached, the directory is checked to see if any files match and need to be processed. 
 
Then, for command (cmd really), issues a directory query to enumerate the files. This query returns only the first file in set. If there are any aditional files that match the file mask in for command, a flag is set that indicates to the caller (cmd) that there are more files to be processed, but the list of the remaining files is not yet retrieved. 
 
When execution of code inside for reachs the end of an iteration, and there are files pending to be read, a query is sent to get the remaining of the list of files pending to be processed and that match the for file selection. 
 
System fills a buffer with the list of files remaining. If at that point the list of files is short enough to be full readed in buffer, the query will not be repeated. If the list of files is big enough to not fit in buffer, partial list is retrieved and when files in retrieved list are processed, the query will be sent again to get more files to process.
 
Number of files in buffer depends on length of filename. Shorter filenames, more files in buffer and less queries to filesystem.
 
This behaviour (retrieving remaining list of files at end of first file processing) is only done if the query for files returns that there are files pending. When one query does not return that flag, no more files are retrieved.
 
EXCEPTIONS
 
If working in NTFS, the files only get included in "requeries" if they are alphabetically greater than the last file that has been processed in for command. 
 
If working if FAT, the query will include all new file generated that match the for command file selection independly of it name. And yes, it can get into an infinite loop. (In tests, the system buffer only retrieve one filename, and requery in each iteration). You can try 
 
break > a.txt && cmd /v:on /c "for %f in (*.txt) do break > !random!.txt"
 
All my tests has been made on a windows 7 64bit, NTFS and FAT32 partition (this on a USB drive). No way to test other configurations. If anyone see a diferent behaviour, please comment.
 
For more information, ZwQueryDirectoryFile