MongoDB for Developers with Python Transcripts
Chapter: MongoDB's shell and native query syntax
Lecture: Concept: Basic querying
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We've explored the shell a little bit, we've done some querying, let's look at the concepts behind it, so you have them nice and concise,
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in case you want to come back for a reference. So if we want to query say the Book collection in the bookstore database
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where the title is 'From the Corner of His Eye', we can type find and give it this little prototypical json object,
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hit enter, and boom everything comes back that has the same title, different isbns, different primary keys and so on, but releases, different versions,
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maybe one is paper back on is kindle, who knows; so the idea is we're going to come up with these prototypical json objects,
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here title: whatever the title is. Now, if we want to do more than just what is the title here
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we want to say give me the book with the title this and the isbn that, given that the isbn is probably unique,
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we could maybe just search for it instead, but we want to demonstrate the and clause, right. So here we'll give it this prototypical sub document
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with the title being the title we're looking for, and the isbn being this one. And notice, now we only get one record back,
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so our prototype will document is basically an and clause, every field must match. We also saw that one of the excellent ways to group related data,
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this would be what you might call an aggregate in domain driven design, is to embed items into the document,
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so here we have ratings that ratings have little sub objects, sub documents that have things like user ids and values
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and at the very beginning, and in the example you saw, the superpower of these document databases, is that they can query them,
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so I want to find all the books that have been rated by this highlighted user id— how do I do that? So we just pretend we're traversing the objects
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Ratings.UserId, so down here we'll say find Ratings.UserId and we give it the object id that we're looking for
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because ''Ratings.UserId'' is not a valid key or a field name in a Javascript object
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we have to put it in quotes, but other than that, it's basically the same idea
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and here we get back all the books that have been rated by this particular user. So we just use this dotted notation to traverse the hierarchy
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one other interesting point is maybe ratings just contained the number like it was at 7,5,... then you could actually just if I want to say
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find all the books that have a rating of seven I could just say find ratings:7, I don't have to do this dot notation or anything like that,
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but because I'm looking within that document inside ratings, regardless of whether it's an array or it's a single rating thing,
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you do it like this that dot notation.