MongoDB for Developers with Python Transcripts
Chapter: Course conclusion
Lecture: Lightning review: Document design
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Next up was document design.
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Some of the concepts and ideas of relational databases still apply here,
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you still are modeling data, you still put it into a database,
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but many of the techniques fall down,
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this whole concept of third normal form
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doesn't make nearly as much sense as it does in a relational database.
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What more we focus on often is really
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how do we make relationships either between documents or within documents.
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We saw the primary question, not the only one, but the most challenging one,
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the one you have to think most carefully about is to embed or not to embed,
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and I gave you a few rules or tips to help you guide this decision.
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One— is the embedded data wanted and you use it 80 percent of the time or more,
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most of the time when you get that containing document?
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If that's true, you probably want to embed,
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if that's false, maybe consider that as a warning sign not to.
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How often do you want the embedded document without the outer containing document?
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If often what you really want to get access to is these little inside pieces,
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there's a lot of overhead and it really kind of complicates the way
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you access it through your application,
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if you want to get them most of the time, or frequently, on their own.
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Is the embedded data abounded set?
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Remember, these documents can only be sixteen megabytes or larger,
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the number is way higher than you really want it to be,
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if this is an unbounded set you're going to continue to add to it,
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it very easily could outgrow the actual size that you're allowed to store.
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Really for a performance reason though, is it abounded set and is that set small?
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Because if you put huge amounts of data in there,
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you're going to really slow down your read time
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for these database operations that involve this document.
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These are the four main rules here,
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you also want to consider how your application accesses this data,
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it might be really easy to answer these four questions
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because there's a very constrained and small set of queries
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you run against your database;
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or it could be that you ask all sorts of questions in a highly varied ways
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in which case it's harder to answer those questions,
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the more types of queries you have the harder it is to know
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whether most of the time you want the embedded data for example.
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The more varied your queries are, the more you'll trend
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towards third normal form, relational style and less embedding.
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One of the situations where you have lots of varied queries is
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if you have this thing called an integration database,
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which we talked about sort of sharing a database across different applications,
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versus having one dedicated to a particular application
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where you can understand these questions very clearly.
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So when you're designing these documents
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you want to really think most carefully about do you want to embed this data
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or create a soft foreign key type of relationship.
