MongoDB for Developers with Python Transcripts
Chapter: Working with MongoDB directly from Python: PyMongo
Lecture: Concept: Atomic updates
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0:01
Let's review the ideas behind these in place updates.
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So here we have more or less a complete MongoDB Python program
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using PyMongo here, so we're going to import PyMongo,
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connect the local database, all the default options,
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and we're going to either create or get access to the bookstore
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by saying client.bookstore, now we're going to insert an object
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that has no favorited by element, right no list, it just has a title and isbn,
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so after the insert, we're going to end up with an _id and a title and an isbn.
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And then maybe we want to add this idea of favorited by,
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maybe you want to design this already that way
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and have an empty list there, but whichever more or less would work the same,
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so we can say I would like to go find the book,
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the first part of our update statement is the where clause,
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so find by primary key and remember, that's when we call insert_one
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that's results.inserted_id, so that's going to find the one and only the item
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and then we're going to use the add to set operator
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and we just pass that as a string in PyMongo,
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and then we'll push on favorited by such and such.
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We could also use $set to set, say $setTitle: the new book with updated title,
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or something like this right, so you can use this all over the place
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and what's really cool, now you may be thinking oh this api is kind of crazy,
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we've got these these dollar operators
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and it's a lot to learn if you're totally new to it, I realize
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but when we get to MongoEngine, you'll see that
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MongoEngine does this transparently under the cover for us,
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so you can actually not have to do this,
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you won't have to necessarily remember all of these
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but you'll get all the benefits that we're describing here.
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If you're using PyMongo, you have to know the api really intimately
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so we're going to push this 1001 user id on to favorited by
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and maybe we'll push 1002 as well
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if people signed up at the same time, they saw the same book, they loved it
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and let's go head and push this 1002 again,
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well not the push operator, but the add to set operator,
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do this again, because it's add to set
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we're going to get a new document that has new book title,
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the same isbn and two items and it's favorited by
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and it's going to be 1001 and 1002, because add to set is item potent
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calling it once or calling it a hundred thousand times,
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it has the same result, other than it might take longer
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to call it a hundred thousand times, right.
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So if it's already there it makes no difference
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but if it's not there to push it in super cool operator,
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really taking advantage of the hierarchical nature of these documents.
