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Welcome back this video I'm going to show you the other way of associating data which is by using object

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references.

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So before we get started I'm going to make a new file here in the same directory and I'll call this

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one.

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References taught J.

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And I'm going to just copy everything over into that file from our previous lesson and I'm going to

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alter this.

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The first thing I'll do is change the database that we use just so that we're not conflicting things

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and we're not overwriting what we just previously did.

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So I'm going to make the name blogg demo underscore too.

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All right.

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And then I'm going to go ahead and just get rid of a lot of stuff in here.

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Pretty much everything aside from our schema that we have in the models.

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And I'll start by talking about what it means to reference data versus embedding it.

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So what we did last time in the last video was we embedded data where we had a user that looks something

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like this with a name and there's an email in there as well.

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And then there is a POST array and each post in that array was actually stored inside the array just

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like this where title and content.

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There we go.

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And we have you know five six as many as we want and hear different posts inside the POST array.

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Now what I'm going to show you in this lesson is very similar except what we actually do is have a poster

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array and inside all that we're going to store in here rather than the actual posts.

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We're going to have a bunch of IDs so we'll have these long IDs that look like that

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and so on.

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And these ideas will correspond to individual posts.

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So then we'll have a post over here that has ID equal to this and it will have title you called something

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else and so on.

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So again the key difference is that we're storing IDs which is where the name reference comes from.

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We're referencing the ID of another post rather than embedding the entire post.

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OK so let's get started.

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And we have to make a few changes to our schema rather than having posts be an array of post schema

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.

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What we actually do make it an array.

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But we're going to pass an object in and the object is going to look like this.

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I mean spaces out just a little bit.

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And our object is going to have two main properties type and ref and type is going to be mongoose that

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schema types dot object id and ref will be post.

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So let's talk about what I just did here.

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I've said that in the user schema there's a post attribute and it's an array but rather than being an

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array of posts like we have here.

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Or it's an array of the post schema.

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It's actually an array of object IDs.

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And this is just the way that we write that syntax.

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It's a mongoose object id belonging to a post and we can save.

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And just to make sure we didn't do anything wrong we can run the file make sure we don't get an error

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.

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Great.

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Now let's get started by creating a single user that we can then add post to later.

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So do user create and this one will give a email of Bob at gmail dot com and a name will be Bob Filcher

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and we'll save and then we'll just leave it like that and we'll just assume that this is going to work

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rather than adding the callback in.

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So this is just going to create our first user.

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So let's run the file.

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All right.

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So we don't see anything but we could go into Mangu and check it out.

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So show Digby's use log demo underscore too and then we can do the users find and we have one user with

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his name.

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Bob Belcher email Bob at gmail dot com and posts that's empty because we haven't added any posts in

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yet.

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So let's get out of here and the next thing I want to do is add a post to this user so I'm going to

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get rid of that create statement and I'll come out so that you can see it and what I'll do is make a

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new post.

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So post doc create and we're making it independently of the user.

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So we're making that post and we'll give it a title of how to cook the best burger and then content

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and not just fill it with blah blah blahs of laws for now just like that and will save and that should

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make us a post and just to make sure this time let's add in the callback error and post and we'll just

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cancel that log post and we're not going to handle the error just for the sake of time and run the file

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.

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And we've now added a new post to the database with an ID.

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Remember this I.D. remember the whole thing 5 6 2 5 8 3 7 8.

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Now I'm just kidding.

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But but remember what it looks like.

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And then we have our content and then our title.

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All right.

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So let's get out of there.

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So what we want to do next is talk about how we can connect a post and a user using that ID.

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And to do that I'm actually going to go through the steps of making another post.

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So let's call this how to cook the best burger.

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Part Two and this will make a new post and once we save that post We're then going to find the user

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PABX.

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So we're going to do a user find and we'll do find one and we'll find your name.

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Let's do e-mail this time where e-mail is Bob at gmail dot com and then we'll run this code afterwards

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ever and then we'll found that we'll call this found user.

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OK.

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So a lot going on.

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So we're creating a post once the post has been created.

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We're finding a user in this case this user here that we've already created and then we're going to

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handle the error if we need to.

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Otherwise we're then going to add the post into the users posts.

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So it's found the user posts which is what we called it up here and we're going to push in push post

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and post is referring to the post that we just created that was safe's the database with title How to

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Cook the Vestberg or to content blah blah blah blah blah.

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We save it if it works.

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We have a post variable that storing the post and then refining the user.

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In this case the one with email Bob at gmail dot com.

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And then if we find it we're then going to add the new post into that users post array.

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Then let's save that.

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So afterwards we need to do another found user does save.

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And yes we need a another callback and this one will have error and let's call this data just to make

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it really clear what's happening.

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And in here I'm just going to again handle the error

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and then if there is no error going to cancel that log data.

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All right man we have a lot here.

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So create a post find the user and then take that post push it into the users posts save the user and

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then when that's done print out the data.

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Let's see what we get.

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All right.

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So it worked.

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Here's our user name Bob Belcher email.

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Here's the user id and then instead of posts all that we have is an array with one item and it's an

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object ID versus when we had the embed J.S. where we were working with embedded data.

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We had the entire post so that this array instead of it we actually saw the data.

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Now we're just seeing the ID

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so.

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So let's go add one more.

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So we'll do part 3.

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And the text of that one instead of blah blah blah.

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It's just going to be jibberish just so that it's easier to tell apart.

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And the consul will add that post.

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Now we have two object IDs here and each one corresponds to an individual post.

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OK.

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So that's how we can associate them.

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But now we need to figure out how do we take this object id and find the correct post.

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Let's say that we want to find a user.

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And then I want to find that users post as well and not just the IDs but I want all of the data.

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So I'm going to clear the console and I'm also going to comment out this behemoth here.

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And so what we want to do is find user and then find all posts for that user.

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And there's actually a way to do that in one go.

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So we need to find the user first.

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So that's user up find and we'll do find one again and then we need to pass and what we're looking for

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which will be email where it's Bob at gmail dot com.

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And then this is something new.

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So we haven't seen this before.

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Dot populate we're going to populate posts and then dot exec and I'll explain all this in just a moment

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.

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OK.

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So what we've done here we've written a longer query that has multiple pieces.

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So we're finding a user.

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And then we're changing this populate posts which will actually populate the field posts look up all

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those object IDs find the correct data and then stick it in the post array and then we run exec to actually

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start the query.

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So it's a little bit weird.

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We're finding one.

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But notice that we're not using a callback in here and we're changing up populate and then we're giving

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it Dot exec at the very end which will actually make all of this happen.

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So then we're passing callback into exec because that's when we're executing the code.

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And if we did this right.

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So let's check if there's an error.

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First Council that log error.

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Otherwise hopefully our user is going to have all the posts pre-populated inside the posts attribute

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so will cancel that log user and let's try running this.

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Make sure everything is commented out except for this.

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Let's run.

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And what do you know.

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It worked.

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So we get a user name is Bob Belsher email Bob at gmail dot com.

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But now post isn't just an array of object IDs.

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It actually has the full post in there.

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Both of them.

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So you can see it does have an idea what we have content and title content and title.

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So to summarize everything that we did we store data that it looks like this here with object IDs.

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You can see the two objects IDs and then we made a second query to retrieve the data and we filled in

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the post Saray with all the data using populate that exec.

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So you might be wondering why we would use one versus the other.

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When would we embed data versus when would we use object id references.

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And it's a really good and really important question that will address as we use them instead of our

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camp.

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The short answer is that it depends.

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And you can get by using either style and pretty much every situation.

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However there usually is one either using references or embedding data that is going to lend itself

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better to whatever you're doing and we'll talk about that as we go through your camp and we start to

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add in comments and users and we add in ratings and photos and all these different features.

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Some of them are going to be embedded and some of them are going to be referenced