Separate login for user / administrators using mongodb I have 2 separate groups of users on my website. One is user and the other one is admin.  Currently I put them in 2 different collections user and admin and login respectively.  My questions is: 


Mongodb generates _id automatically for both user and the admin collection.  Since they're in 2 different collections chances are one day you created one user and one admin with the same _id right?  So it seems the only way is to check all documents in both dbs and make sure your newly created user (or admin) does not have repeated _id right?  Is there something I can do natively in mongodb to make this happen without checking? 
I can also put all users and admins in one collection.  This way I don't have a problem but I am not sure if I should do this.


p.s: because I have a table keeping track of user / admin balances so I certainly don't want the _id to repeat
p.s2: the db is taking longer and longer to query.  Also my ORM creates user instances and generated _id automatically for me.  I am not sure if I should just generate an _id and create it this way...

Any comments are greatly appreciated.  Thanks!!
You should not have two collections, that will give you headache. 

Have a user collection which has admin and regular users.  You can then query users as a whole or look for a given type only. So if you are looking for user id x you don't have two search two collections.

As for the question on duplicate ids with 2 collections, it simply depends how the ids are generated.  You say your ORM does it... so you will need to check the doc on how it does it.