In my (limited) experience with Mongo, its just not like that.
You can't just (quickly) query any key in the document - you have to define indexes anyway or you'll be doing the equivalent of a table scan or Map/Reduce.
Document databases shine when you're just not doing that kind of query anyway, and you've got a ton of data to store. If you need to do e.g., fulltext and/or geospatial search you should probably use a search server anyway (I like Sphinx), and then just lookup by PK in whatever datastore you're using.
Its been mentioned elsewhere on this thread, but I'm also quite fond of the old FriendFeed method: serialize your arbitrary data into a (MySQL) BLOB, and then run a background process to build "indexes" (really tables) when you find out you need them.
Its ridiculously simple to start doing that, and there's no new tech to learn.
You can't just (quickly) query any key in the document - you have to define indexes anyway or you'll be doing the equivalent of a table scan or Map/Reduce.
Document databases shine when you're just not doing that kind of query anyway, and you've got a ton of data to store. If you need to do e.g., fulltext and/or geospatial search you should probably use a search server anyway (I like Sphinx), and then just lookup by PK in whatever datastore you're using.
Its been mentioned elsewhere on this thread, but I'm also quite fond of the old FriendFeed method: serialize your arbitrary data into a (MySQL) BLOB, and then run a background process to build "indexes" (really tables) when you find out you need them.
Its ridiculously simple to start doing that, and there's no new tech to learn.