GridFS - MongoDB Basics - page 109

Retrieving Files from MongoDB
So far, you haven't actually pulled any files out from MongoDB. The most important
feature of any database is that it lets you find and retrieve data once it's been put in. The
following snippet retrieves a file from MongoDB using the mongofiles command get :
$ mongofiles get /tmp/dictionary
connected to: 127.0.0.1
done write to: /tmp/dictionary
$
This example includes an intentional mistake. Because it specifies the full name and
path of the file you want to retrieve (as required), mongofiles writes the data to a file with
the same name and path. Effectively, this overwrites the original dictionary file! This isn't
exactly a great loss, because it is being overwritten by the same file—and the dictionary
file was only a temporary copy in the first place. Nevertheless, this behavior could give
you a rather nasty shock if you accidentally erase two weeks of work. Trust us, you won't
figure out where all your work went until sometime after the event! As when using the
delete command, you need to be careful when using the get command.
Summing Up mongofiles
The mongofiles utility is a useful tool for quickly looking at what's in your database. If
you've written some software, and you suspect something might be amiss with it, then
you can use mongofiles to double-check what's going on.
It's an extremely simple implementation, so it doesn't require any fancy logic that
could complicate accomplishing the task at hand. Whether you would use mongofiles in
a production environment is a matter of personal taste. It's not exactly a Swiss army knife;
however, it does provide a useful set of commands that you'll be grateful to have if your
application begins misbehaving. In short, you should be familiar with this tool because
someday it might be exactly the tool you require to solve an otherwise nettlesome
problem.
Exploiting the Power of Python
At this point, you have a solid idea of how GridFS works. Next, you will learn how to
access GridFS from Python. Chapter 2 covered how to install PyMongo; if you have any
trouble with the examples, please refer back to Chapter 2 and make sure everything is
installed correctly.
If you've been following along with the previous examples in this chapter, you should
now have one file in GridFS. You'll also recall that the file is a dictionary file, so it contains
a list of words. In this section, you will learn how to write a simple Python script that
prints out all the words in the dictionary file. Sure, it would be simpler and more efficient
to simply cat the original file—but where would the fun be in that?