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I have started using MongoDB and I am fairly new to it.
Is there any way by which I can apply constraints on documents in MongoDB?
Like specifying a primary key or taking an attribute as unique?
Or specifying that a particular attribute is greater than a minimum value?
Being a “schemaless” database, some of the things you mention must be constrained from the application side, rather than the db side. (such as “minimum value”)
However, you can create indexes (keys to query on–remember that a query can only use one index at a time, so it’s generally better to design your indexes around your queries, rather than just index each field you might query against):
http://www.mongodb.org/display/DOCS/Indexes#Indexes-Basics
And you can also create unique indexes, which will enforce uniqueness similar to a unique constraint (it does have some caveats, such as with array fields):
http://www.mongodb.org/display/DOCS/Indexes#Indexes-unique%3Atrue