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‫So we embedded users

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‫into tours in the last video,

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‫and also talked about the drawbacks

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‫of that approach in our specific situation.

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‫And so in this video let's actually connect tours

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‫and users not by embedding but instead by a reference.

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‫And so to start, let's actually get rid

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‫of the code we wrote in the last lecture.

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‫Okay, so this one here,

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‫responsible for performing the embedding basically.

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‫And now let's go here to our guides field.

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‫Okay?

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‫So this time in this video,

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‫the idea is that tours and users will always remain

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‫completely separate entities in our database.

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‫Okay?

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‫So all we save on a certain tour document

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‫is the IDs of the users that are the tour guides

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‫for that specific tour.

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‫Then when we query the tour,

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‫we want to automatically get access to the tour guides.

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‫But again, without them being actually

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‫saved on the tour document itself.

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‫And that exactly is referencing.

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‫So just as we talked about by the beginning of this section.

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‫All right?

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‫And so let me now show you

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‫how we can implement referencing using Mongoose.

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‫Okay?

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‫So, here in the guides we will now want to specify an array.

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‫Okay?

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‫So just like we did before with the locations.

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‫And so that then again means

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‫that these will be some sub-documents.

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‫So embedded documents.

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‫All right?

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‫And now the type is going to be

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‫a new type that we never saw before.

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‫And that is mongoose.Schema.objectId.

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‫Okay?

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‫And what this means is that we expect

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‫a type of each of the elements

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‫in the guides array to be a MongoDB ID.

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‫All right?

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‫And here actually it needs to be a capital O,

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‫okay, otherwise it's not gonna work,

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‫and also all of this here needs to be inside of an object,

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‫just like any other schema type definition.

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00:02:06,880 --> 00:02:09,403
‫Okay, because that's all this really is.

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00:02:11,140 --> 00:02:16,140
‫Okay, so the type is of this MongoDB ID, basically,

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‫and then we also need to now specify the reference.

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‫And this is where the magic happens behind the scenes,

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‫because here, now we say that the reference should be user.

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‫Okay, and so this really is how we establish references

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‫between different data sets in Mongoose.

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‫And for this we actually do not even need

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‫to have the user to be imported into this document.

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‫So we actually had that here, but we don't even need it.

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‫We had that here for the previous lecture,

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‫but we can comment it out,

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‫because what we just did here is still gonna work.

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‫Okay?

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‫So, let's now go ahead and create a new tour,

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‫and actually I'm going to do it just the way we did before.

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00:03:01,440 --> 00:03:03,973
‫So let's just go ahead and delete this one.

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‫Where is the ID?

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‫Here we go.

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‫So delete tour.

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‫So we can use our API for that already.

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‫All right, and now we create a new tour.

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‫And so just like before,

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‫all we pass into the guides is an array of the IDs.

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‫All right?

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‫But this time we actually specified

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‫that an object ID is exactly what we expect.

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‫Right?

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‫So, this here is of the type object ID.

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‫But behind the scenes, it's also referenced to the user.

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‫All right?

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00:03:44,200 --> 00:03:47,300
‫So, when we now create this tour here,

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‫it will actually only contain these IDs,

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‫and not the user corresponding to the IDs.

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‫So let's take a look at that.

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‫And so yeah, here we go.

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00:03:59,040 --> 00:04:01,720
‫So this is exactly the data that we put in.

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00:04:01,720 --> 00:04:04,430
‫Just the IDs of the tour guides.

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00:04:04,430 --> 00:04:07,010
‫Okay, and that's exactly what we were expecting.

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00:04:07,010 --> 00:04:09,410
‫Because for now, all we really have

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‫is the references inside Mongoose.

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‫And we will then take care of actually getting the data

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‫to show up in our output in the next video.

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00:04:17,730 --> 00:04:20,330
‫Okay, because we will do that in two different ways.

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00:04:21,210 --> 00:04:24,323
‫Let's also take a look here at Compass really quick,

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00:04:25,930 --> 00:04:30,930
‫just to see that as well where is that, yeah, here.

95
00:04:30,960 --> 00:04:33,680
‫So you see object ID actually,

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00:04:33,680 --> 00:04:36,480
‫and then of course, the IDs that we passed in.

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00:04:36,480 --> 00:04:39,960
‫So just as we expected with tours and users,

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00:04:39,960 --> 00:04:42,620
‫still two completely different entities.

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00:04:42,620 --> 00:04:44,860
‫And as I said before, in the next video,

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‫we will then take care of actually displaying

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00:04:47,290 --> 00:04:49,030
‫the user data in the output,

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00:04:49,030 --> 00:04:51,533
‫using a process called populating.