MarkLogic：在某些情况下将文档从一个目录移动到另一个目录

Question

I'm new to MarkLogic and trying to implement following scenario with its Java API:

1. For each user I'll have two directories, something like:

   1.1. user1/xmls/recent/

   1.2. user1/xmls/archived/

2. When user is doing something with his xml - it's put to the "recent" directory;
3. When user is doing something with his next xml and "recent" directory is full (eg has some amount of documents, let's say 20) - the oldest document is moved to the "archived" directory;
4. User can request all documents from the "recent" directory and should get no more than 20 records;
5. User can remove something from the "recent" directory manually; In this case, if it had 20 documents, after deleting one it must have 19;
6. User can do something with his xmls simultaneously and "recent" directory should never become bigger than 20 entries.

Questions are:

1. In order to properly handle simultaneous adding of xmls to the "recent" directory, should I block whole "recent" directory when adding new entry (to actually add it, check if there are more than 20 records after adding, select the oldest 21st one and move it to the "archived" directory and do all these steps atomically)? How can I do it?
2. Any suggestions on how to implement this via Java API?
3. Is it possible to change document's URI (eg replace "recent" with "archived" in my case)?
4. Should I consider using MarkLogic's collections here?

I'm open to any suggestions and comments (as I said I'm new to MarkLogic and maybe my thoughts on how to handle described scenario are completely wrong).

Answer 1

1. You can achieve atomicity of a sequence of transactions using Multi-Statement Transactions (MST)
2. It is possible to MST from the Java API: http://docs.marklogic.com/guide/java/transactions#id_79848
3. It's not possible to change a URI. However, it is possible to use an MST to delete the old document and reinsert a new one using the new URI in one an atomic step. This would have the same effect.
4. Possibly, and judging from your use case, unless you must have the recent/archived information as part of the URI, it may be simpler to store this information in collections. However, you should read the documentation and evaluate for yourself: http://docs.marklogic.com/guide/search-dev/collections#chapter

Answer 2

Personally I would skip all the hassle with separate directories as well as collections. You would endlessly have to move files around, or changes their properties. It would be much easier to not calculate anything up front, and simply use lastModified property, or something alike, to determine most recent items at run-time.

HTH!