使用erlang mongodb驱动程序进行数据库操作的正确方法是什么？ [英] What's the right way to use erlang mongodb driver to make a db action?

问题描述

我正在尝试官方的mongodb erlang司机。我阅读了文档，还有一些我不明白的东西。希望有人可以告诉我使用它的正确方法：

每次我采取行动，我只是写下如下内容：

  {ok，Conn} = mongo：connect（{localhost，27017}）。 
 mongo：do（safe，master，Conn，test，fun（） - > 
 mongo：save（foo，{'_id'，1，bbb，22，y，2}），
 mongo：save（foo，{'_id'，4，bbb，22，y，2}）end）。 
 mongo：disconnect（）。 
  

1. 这是一个正确的方法吗？每当我完成数据库操作， Conn 似乎死了。或者我应该保持 Conn 而不是断开它，以便下次重用？没有全局变量可以保持 Conn ，所以我想出来的唯一方法是使用类似 gen_server 并在其州保留 Conn 以供重用。这是正确的方法吗？




2. 我还看到有一个 connect_factory 方法。但是我不能弄清楚处理它的正确方法。一个比连接处理大量db操作更好的方式是 connect_factory ？如何通过使用 connect_factory ？


c> Conn li>

这是一个与mongodb不相关的问题。我想给每个用户一个唯一的号码，当他们访问。所以我在数据库中保存了一个计数器，当用户访问时，计数器被加1并返回给用户作为唯一的数字。但是我一直都关心两位用户在同一时间读取数据库的数量。使用mongodb如何使独特的计数器增加1？

非常感谢！

解决方案

1. 如果您的操作有错误，Conn可能会死机，否则应该是可重用的。注意，mongo：do返回{failure，X}错误。如果要重复使用，请勿断开连接。 BTW，断开连接将Conn作为参数。如果要将Conn保留在全局变量中，请参考Erlang文档以了解如何执行此操作（例如，ets表，gen_server等）。此外，请查看此驱动程序中的mvar模块，以获取一个包含值的简单gen_server。


2. connect_factory用于维护可重用的连接池。请阅读 http://github.com/TonyGen/mongodb-erlang 上的教程。在底部显示如何使用connect_factory与resource_pool。


3. 您可以使用MongoDB进行原子增量。请参阅 http://www.mongodb.org/display/DOCS/Atomic+Operations，特别是findAndModify。

I am trying official mongodb erlang driver. I read the doc and there's still something I can't understand. Hope anyone can tell me what's the right way to use it:

Every time I make an action, I just write something as follows:

{ok, Conn} = mongo:connect ({localhost, 27017}).
mongo:do (safe, master, Conn, test, fun() ->
    mongo:save (foo, {'_id', 1, bbb,22, y,2}),
    mongo:save (foo, {'_id', 4, bbb,22, y,2}) end).
mongo:disconnect().

1. Is this a right way? Everytime I finished a db action, Conn seems died. Or should I keep the Conn rather than disconnect it to reuse it for next time? There's no global variable to keep Conn so the only way I can think out to make it is to use something like gen_server and keep Conn in its State for reuse. Is this the right way?

2. I also see there's a connect_factory method. But I can't quite figure out the proper way to deal with it. Is connect_factory a better way than connect to deal with large amount of db actions? And how to get a workable Conn by using connect_factory?

3. This is a question not quite related with mongodb. I want to give every user a unique number when they visit. So I saved a counter in db, when a user visit, the counter is added by 1 and returned to the user as the unique number. But I always have concern about two users get the same number with reading db at the same time. How can I make a unique counter increased by 1 using mongodb?

Thanks very much!

解决方案

1. Conn may die if your action had an error, otherwise it should be reusable. Note, mongo:do returns {failure, X} on error. Don't disconnect Conn if you want to reuse it. BTW, disconnect takes Conn as an argument. If you want to keep Conn in a global var then consult the Erlang documentation for ways to do this (eg. ets table, gen_server, etc). Also, check out the mvar module in this driver for a simple gen_server that holds a value.
2. connect_factory is used for maintaining a reusable pool of connections. Read the tutorial at http://github.com/TonyGen/mongodb-erlang. At the bottom it shows how to use connect_factory with resource_pool.
3. You can atomically increment using MongoDB. See http://www.mongodb.org/display/DOCS/Atomic+Operations, in particular findAndModify.

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