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At the end of last video I mentioned that getting TypeScript and Mongoose to work together is sometimes

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just a little bit awkward.

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So in this video I want to outline two big issues that we're going to run into just so you are aware

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of why we're going to write out some slightly complicated code in just a moment.

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So here's the big issues that are going to start to run into.

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First I want to give you a quick review on some terminology around Mongoose and Mongo DV inside of Mongo

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DV.

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We organize information into different collections.

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We might have a user collection that will store all the different users who have signed up for our application.

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So in this case users on through for each of these can be thought of as little objects that store some

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information about a very particular user to access all this data.

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We're going to use Mongoose and in particular we are going to create two different things inside a mongoose.

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We are first going to create something called a mongoose user model.

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This is a class that is going to represent the entire collection of users.

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So we will use this user model class to run queries to create new users or to do anything that modifies

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or queries the overall collection.

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We are also gonna have something called a mongoose user document a user document is also a class.

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It is meant to represent one singular user so we might create an instance of a user document to represent

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user number 2 or create a second instance or another instance to represent just user number for.

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So again we've got a user model that represents all of our data and user document that represents just

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one little thing.

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So that quick refresher on terminology.

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Here are the two issues that are going to start to run into when we are getting Mongoose and typescript

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to interact with each other so issue number one is going to come up when we start to create a new user

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document.

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So this is going to be how we eventually try to create a new user document or a new instance of a user

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will say new user and then pass in some different properties such as email and password and whenever

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we tried to pass in properties to anything typescript wants to understand the properties we are passing

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in and somehow make sure that you're passing in the correct type of data the typescript wants to understand

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the different arguments that calling new user is going to accept.

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However Mongoose does not make this easy behind the scenes or more specifically with the Mongoose type

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definition file that we just installed a little bit ago.

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Whenever we try to create an instance of a user as you're doing right here it is not going to kind of

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tell typescript about the different properties that we are trying to pass in.

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And so for example we could make a huge typo inside of here we could accidentally write in hard instead

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of password and typescript is not going to complain because typescript is not going to be given enough

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information by Mongoose by default to understand the different types of arguments or the names of these

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properties we are supposed to pass in but this is issue number one that we are going to Ryan too.

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We have a workaround for this.

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We're going to essentially somehow teach typescript about the different properties that this constructor

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expects.

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So we are going to solve this.

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I just want you to be aware that this is something we need to be aware of.

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OK.

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Issue number two.

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So with issue number two at some point time we are going to create a new user.

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And we might assign it some properties like say email and password that's been going to give us back

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a user document.

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So that's let's imagine right here a user variable or something like that at some point time later.

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We're going to want to access some of the data within this user.

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Let's imagine for a second that we add in a console log of user if we did that we might end up seeing

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that this user document has more properties than what we provided to the constructor.

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So for example we might take that email and password and assign them as properties to user.

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But behind the scenes Mongoose might decide to add in a couple of additional properties as well.

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Properties like let's say a created at timestamp or in updated that timestamp so the properties that

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we pass into the constructor don't necessarily match up with all the properties that are created on

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the user documents.

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This is also an issue with typescript because typescript wants to know about all the properties that

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exist on the user.

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So we need to somehow tell typescript hey look we're going to pass some properties into the constructor

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typescript but don't worry there are going to be some other properties that get created behind the scenes

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and assigned to the user as well.

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So we really need to teach typescript that there are kind of two different sets of properties.

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There's one set of properties that will be passed to the constructor and there's gonna be a second set

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of properties that we should be able to access on the user document that gets created.

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That is issues number one and number two.

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And again this is some stuff that we're going to have to fight with around Mongoose and typescript.

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Now of course if we were just writing javascript yeah we would not really have to worry about this but

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there are some very good reason.

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So you're using typescript on this micro services project.

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We haven't really dove into them just yet but trust me you're going to start to see why we're using

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typescript very quickly as soon as we start to create our second service.

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All right.

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Now we understand these two big challenges.

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Another quick pause.

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We're gonna start to write out some code that's going to solve both these challenges.

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We're going to create our user model and all that good stuff.

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So I'll see you in just a minute.