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‫Let's now keep working on our API.

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‫Over the next videos, we will implement

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‫a couple of common API features

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‫that make an API easier and more pleasant to use

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‫for whomever is gonna use it.

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‫And in this lecture,

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‫we're gonna start with filtering.

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‫So again, the first feature that we're gonna implement

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‫is to allow the user to basically filter data

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‫using a query string.

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‫Let me just tell you what a query string is using Postman.

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‫So, let's close all these guys.

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‫Alright.

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‫Actually where filtering is gonna make sense

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‫is here on this get all tours route.

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‫Because, this is the one that,

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‫well as the name says, gets all the tours.

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‫And so here, we want to allow the user to filter the data,

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‫so that instead of getting all the data,

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‫he only gets the data that matches the filter.

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‫Like this, we can basically allow the user

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‫to query the data in a very easy way.

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‫Again, using the query string.

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‫And the query string looks a bit like this.

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‫And I'm sure you've seen it.

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‫So we start with a question mark,

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‫and then we can simply specify some field value pairs.

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‫So let's say we wanted to filter

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‫for a duration equal to five and

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‫at the same time, a difficulty of easy.

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‫So we can very simply build a query string like this.

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‫So again, it starts with this question mark,

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‫and then we can specify as many

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‫key value pairs using this format.

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‫And now our Postman application here

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‫actually recognizes this and basically

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‫parses this string here and puts the key and

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‫the values down here in this Params tab.

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‫So we could also specify the key and values here.

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‫So lets say test, set it to twenty three, and

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‫so you see up here that it actually

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‫added it to the query string.

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‫So that's a very nice way of Postman helping us here.

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‫Because now we can, for example, while we're

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‫doing testing we can turn these on and off

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‫and you see that the query string

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‫in here reacts accordingly.

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‫Anyway, we now need a way of accessing this data

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‫that's in a query string, in our Express application.

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‫But, luckily for us, that's very easy,

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‫because Express already took care of that.

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‫So that's just one of the many many things

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‫that Express does for us in order to really make

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‫NodeJS development a lot faster.

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‫So let me show it to you here, actually in the console.

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‫So this data is on a request, which makes sense,

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‫and then it is in a field called query.

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‫So request dot query should then give us

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‫an object nicely formatted with the data

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‫from the query string.

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‫Give it a save.

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‫And note, how I actually added it to

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‫the get all tours handler function.

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‫So again, we do this kind of filtering

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‫in the route where we want to get all the tours.

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‫Let's test it out now with this exact query string.

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‫Sent the request.

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‫And coming back, here we got the object.

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‫Let's actually make this here bigger

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‫so you can see.

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‫That's not really working.

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‫So sometimes I know some people cannot see

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‫the bottom of the screen.

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‫Let me just do it again here.

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‫And so, here we go.

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‫We have the object, which has the duration set to five

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‫and the difficulty set to easy.

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‫And so you see that Express, very nicely,

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‫parsed that string into this, easy to use, object.

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‫Now one thing that I noticed here is that

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‫we're actually missing the log that we had

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‫easier here in the console.

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‫Let's take a look at why that's happening.

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‫So for some reason, we now have the application

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‫before we actually read the environment variable.

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‫That way, the application does not get access to them.

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‫I thought that I had fixed this before,

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‫but for some reason it's back now.

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‫Give it another save here.

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‫And I will try that again.

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‫Now we get our logging back.

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‫A get request to this URL and then with

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‫this rest of the data here.

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‫Anyway, let's now actually use that data

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‫in order to implement our filtering.

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‫But before we can do that, I need to tell you that

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‫in Mongoose, there are actually two ways of

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‫writing database queries.

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‫The first one is to just use filter object

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‫just like we did in the MongoDB introduction section.

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‫Right? Remember that?

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‫The second way is to use some special Mongoose methods.

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‫Let me just, very quickly, show that to you.

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‫With the filter object, we would do it like this.

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‫We start with the find here, and then in there

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‫we can pass a filter object.

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‫And I already mentioned that before.

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‫Again, it works the exact same way as

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‫with a normal MongoDB query.

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‫We could now say, duration

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‫set it to five.

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‫And then,

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‫difficulty, set it to easy.

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‫That's exactly the query string we had before,

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‫and now I'm hard coding it here just to

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‫show you the two different ways of

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‫writing queries in Mongoose.

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‫Let's test this one out.

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‫You see that now, we only get two results.

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‫Let's give ourselves some space here.

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‫Alright.

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‫We see the two results and indeed

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‫they both have a duration of five,

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‫so here and here, and they both are easy.

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‫Easy and easy.

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‫So our filter worked just fine.

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‫That is the first way of writing a query.

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‫Just the normal way that we're already used to,

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‫but there is another way.

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‫Let me show that to you as well.

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‫Again, we start in the exact same way,

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‫but then the difference is that we start

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‫chaining some special Mongoose method to

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‫basically build the query similar to this one that we have.

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‫So we say,

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‫where

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‫the duration

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‫equals five.

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‫Then also, where

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‫the difficulty,

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‫that needs to be in quotes,

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‫equals

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‫easy.

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‫This query here is gonna be exactly

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‫the same as this one, but again, written using

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‫special Mongoose methods.

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‫And there are of course tons of other methods.

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‫For example, instead of equals, we can have less than,

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‫or equal, or just less than, or you can also

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‫sort the results or limit the number of results,

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‫and really all kinds of stuff.

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‫For sure, we're gonna use some of them

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‫over the next couple of videos.

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‫This might look a bit weird here to you,

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‫but its actually very, very useful in some cases.

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‫Just to test, give it a try again to this one.

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‫And indeed we get our same two results.

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‫Now, let me comment this one here out.

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‫I'm gonna leave it here just as a reference,

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‫because right now, we're gonna use this method here.

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‫And we're gonna use it, because in fact,

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‫we actually already have an object that

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‫looks a lot like this.

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‫And that is request dot query.

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‫If you compare it, this object,

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‫to this object that you see down here,

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‫looks exactly the same as this one.

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‫To implement a very simple filter,

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‫all we have to do in this case is to say, req dot query.

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‫Let's try that one more time.

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‫Get rid of this here.

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‫And indeed we get the exact same two results.

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‫Now let's just try only with difficulty set to easy.

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‫Now we get four results.

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‫All of them of course will have

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‫the difficulty set to easy.

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‫Our filter, our very basic filter,

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‫is now actually working.

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‫Now, the problem with this implementation,

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‫is that its actually way too simple.

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‫That's because, later on, we will have

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‫other query parameters.

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‫For example, sort, for sorting functionality,

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‫or page, for pagination.

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‫We need to make sure that we are

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‫not querying for these in our database.

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‫For example, if we added here,

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‫page, equal to two,

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‫then we would, of course, not get any result.

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‫Let me show that to you.

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‫And indeed we do not get any result,

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‫because there is no document in this collection

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‫where page is set to two.

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‫We only want to use this parameter here,

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‫or this field, page, to implement pagination

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‫and not to actually query in the database.

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‫So what we will have to do is,

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‫to basically exclude these special field names

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‫from our query string before we actually do the filtering.

200
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‫Let's now go ahead and implement that.

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00:10:05,540 --> 00:10:08,200
‫What we will do is, to first, create a

202
00:10:08,200 --> 00:10:12,333
‫shallow copy of the request dot query object.

203
00:10:15,690 --> 00:10:17,670
‫Let's call it query object.

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00:10:17,670 --> 00:10:20,030
‫Here we need, really, a hard copy.

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00:10:20,030 --> 00:10:23,560
‫We can't just do, request dot query,

206
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‫because then, if you would delete something

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‫from this object, we would also delete it

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‫from the req dot query object.

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00:10:30,700 --> 00:10:32,170
‫And that's because in JavaScript,

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‫when we set a variable to another object,

211
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‫that new variable will basically just be

212
00:10:37,490 --> 00:10:39,683
‫a reference to that original object.

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‫So we really need a hard copy here.

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00:10:43,770 --> 00:10:46,310
‫In JavaScript, there's not really a built-in way

215
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‫of doing this, but a very nice trick that we can use,

216
00:10:49,020 --> 00:10:53,520
‫since ES6, is to use, first, the structuring

217
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‫which we use by using dot dot dot.

218
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‫And then we can simply create a

219
00:10:58,270 --> 00:10:59,663
‫new object out of that.

220
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‫Just like this.

221
00:11:03,260 --> 00:11:05,420
‫This structuring here, these three dots,

222
00:11:05,420 --> 00:11:08,683
‫will basically take all the fields out of the object.

223
00:11:09,860 --> 00:11:11,810
‫Here with the curly braces, well,

224
00:11:11,810 --> 00:11:13,990
‫we simply create a new object.

225
00:11:13,990 --> 00:11:15,940
‫So we have a new object that is basically

226
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‫going to contain all the key value pairs

227
00:11:18,070 --> 00:11:21,053
‫that were in our req dot query object.

228
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‫So that's a copy.

229
00:11:24,330 --> 00:11:26,450
‫Now let's create an array of

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‫all the fields that we want to exclude.

231
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‫I'm calling that one excluded fields.

232
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‫And then we want to exclude page,

233
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‫so that's the one that I just

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‫told you before in Postman.

235
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‫Then, we also want to exclude

236
00:11:43,170 --> 00:11:44,440
‫sort,

237
00:11:44,440 --> 00:11:46,053
‫we want to exclude limit,

238
00:11:47,890 --> 00:11:50,533
‫and we want to exclude fields.

239
00:11:52,160 --> 00:11:54,940
‫We will implement all of the functionality

240
00:11:54,940 --> 00:11:58,210
‫of paging, sorting, limiting, and selecting

241
00:11:58,210 --> 00:12:01,140
‫only some specific fields, later

242
00:12:01,140 --> 00:12:02,690
‫over the next couple of videos.

243
00:12:03,750 --> 00:12:05,900
‫Next, what we need to do is to

244
00:12:05,900 --> 00:12:08,610
‫basically remove all of these fields

245
00:12:08,610 --> 00:12:10,230
‫from our query object.

246
00:12:10,230 --> 00:12:11,690
‫And in order to do that, we will

247
00:12:11,690 --> 00:12:13,523
‫loop over these fields.

248
00:12:14,660 --> 00:12:15,860
‫So, excluded fields

249
00:12:17,690 --> 00:12:19,070
‫for each.

250
00:12:19,070 --> 00:12:20,390
‫And we're using for each because

251
00:12:20,390 --> 00:12:22,423
‫we don't want to save a new array.

252
00:12:24,150 --> 00:12:25,840
‫Then each of these of elements,

253
00:12:25,840 --> 00:12:27,863
‫we can use the delete operator.

254
00:12:30,930 --> 00:12:32,530
‫And then from the query object,

255
00:12:32,530 --> 00:12:34,730
‫we want to delete the field with

256
00:12:34,730 --> 00:12:36,700
‫the name of element, so the current

257
00:12:36,700 --> 00:12:38,820
‫element in the array.

258
00:12:38,820 --> 00:12:42,340
‫Like this, we will first delete the field of page,

259
00:12:42,340 --> 00:12:45,563
‫then the sort, then the limit, then the fields.

260
00:12:46,560 --> 00:12:48,440
‫Of course, only in case if its there.

261
00:12:48,440 --> 00:12:50,860
‫If there is, for example, no limit field,

262
00:12:50,860 --> 00:12:54,030
‫then, of course, that will not be deleted,

263
00:12:54,030 --> 00:12:55,130
‫because its not there.

264
00:12:56,530 --> 00:12:59,233
‫Let's now take a look if this actually works.

265
00:13:00,380 --> 00:13:02,530
‫I'm gonna log req dot query and

266
00:13:02,530 --> 00:13:05,723
‫at the same time our query object.

267
00:13:08,742 --> 00:13:09,692
‫Giving this a save.

268
00:13:10,600 --> 00:13:12,060
‫Don't worry about our results now.

269
00:13:12,060 --> 00:13:14,190
‫All I want to take a look at is

270
00:13:14,190 --> 00:13:17,080
‫our query object, just to make sure

271
00:13:17,080 --> 00:13:19,530
‫that this logic that we have here actually works.

272
00:13:21,540 --> 00:13:26,540
‫Let's add a sort here of one and a limit of 10.

273
00:13:27,260 --> 00:13:29,210
‫These will make more sense later.

274
00:13:29,210 --> 00:13:30,540
‫For now, I am just adding them,

275
00:13:30,540 --> 00:13:32,293
‫so that I can later exclude them.

276
00:13:34,490 --> 00:13:37,120
‫Results don't matter, all that matters,

277
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‫is that our original query is this one here,

278
00:13:40,640 --> 00:13:42,820
‫and then our query object, which is

279
00:13:42,820 --> 00:13:44,010
‫the one that we're going to use,

280
00:13:44,010 --> 00:13:46,320
‫only has difficulty set to easy.

281
00:13:46,320 --> 00:13:49,723
‫That's because we excluded, page, sort, and limit.

282
00:13:51,000 --> 00:13:53,460
‫This now works, so instead of using

283
00:13:53,460 --> 00:13:57,033
‫req dot query, we're gonna use our query object.

284
00:13:59,390 --> 00:14:03,000
‫Let's get rid of that and try it again.

285
00:14:03,000 --> 00:14:05,080
‫Now we should be back to querying for

286
00:14:05,080 --> 00:14:07,180
‫all the documents that have a difficulty

287
00:14:07,180 --> 00:14:11,473
‫set to easy and ignoring all of these other fields.

288
00:14:13,256 --> 00:14:14,150
‫Send that.

289
00:14:14,150 --> 00:14:15,930
‫And indeed, we are back to our four

290
00:14:15,930 --> 00:14:18,623
‫results that we had before.

291
00:14:19,900 --> 00:14:22,610
‫We can also turn on the duration,

292
00:14:22,610 --> 00:14:24,743
‫and indeed, we will now have two results.

293
00:14:26,110 --> 00:14:27,180
‫Remember that?

294
00:14:27,180 --> 00:14:28,643
‫And if we turn these off,

295
00:14:29,960 --> 00:14:32,380
‫well, then off course its gonna work the same.

296
00:14:32,380 --> 00:14:34,330
‫Let's just delete this empty line here.

297
00:14:36,740 --> 00:14:40,340
‫And so, indeed, with our original query string,

298
00:14:40,340 --> 00:14:42,693
‫things obviously also still worked the same.

299
00:14:44,220 --> 00:14:47,630
‫We prepared our filter feature so that it

300
00:14:47,630 --> 00:14:51,410
‫ignores page, sort, and limit fields.

301
00:14:51,410 --> 00:14:53,450
‫But there is actually something more we need

302
00:14:53,450 --> 00:14:56,210
‫to do in our code, in order to basically

303
00:14:56,210 --> 00:14:59,753
‫be able to implement these features in future videos.

304
00:15:01,360 --> 00:15:03,250
‫Let's go back here to our code.

305
00:15:03,250 --> 00:15:04,570
‫So let's now learn a little bit

306
00:15:04,570 --> 00:15:07,093
‫about how queries actually work in Mongoose.

307
00:15:08,220 --> 00:15:09,910
‫I think I mentioned this before,

308
00:15:09,910 --> 00:15:13,400
‫but its very important to talk about this again.

309
00:15:13,400 --> 00:15:16,943
‫This find method here is going to return a query.

310
00:15:18,060 --> 00:15:20,430
‫All of this here will return a query.

311
00:15:20,430 --> 00:15:22,410
‫And that is the reason why we can then

312
00:15:22,410 --> 00:15:24,840
‫chain other methods like this.

313
00:15:24,840 --> 00:15:28,630
‫Like where, equals, and all these other methods

314
00:15:28,630 --> 00:15:30,770
‫that I talked to you about before.

315
00:15:30,770 --> 00:15:33,770
‫Let me actually show that to you in the documentation again.

316
00:15:37,670 --> 00:15:40,170
‫Here we have the query object,

317
00:15:40,170 --> 00:15:42,710
‫and again, when we use the find method,

318
00:15:42,710 --> 00:15:46,590
‫it will return an object which is a query.

319
00:15:46,590 --> 00:15:48,310
‫So in query dot prototype,

320
00:15:48,310 --> 00:15:50,180
‫we then have all of these methods.

321
00:15:50,180 --> 00:15:52,820
‫For example, down here we have where,

322
00:15:52,820 --> 00:15:54,040
‫which I just mentioned.

323
00:15:54,040 --> 00:15:55,790
‫We have sort which is the one

324
00:15:55,790 --> 00:15:58,120
‫that were gonna use later to sort.

325
00:15:58,120 --> 00:16:00,870
‫We have, let's see, we have less than

326
00:16:00,870 --> 00:16:03,740
‫or less than equal, we have greater.

327
00:16:03,740 --> 00:16:05,260
‫We have...

328
00:16:05,260 --> 00:16:06,700
‫What else did we use?

329
00:16:06,700 --> 00:16:08,070
‫We used equals.

330
00:16:08,070 --> 00:16:11,310
‫All of these are part of query dot prototype.

331
00:16:11,310 --> 00:16:13,920
‫Which, again, refers to objects that

332
00:16:13,920 --> 00:16:16,783
‫we're creating using the query class.

333
00:16:19,613 --> 00:16:21,410
‫Again, this is the reason why

334
00:16:21,410 --> 00:16:24,070
‫we can do this sort of chaining.

335
00:16:24,070 --> 00:16:26,290
‫Now comes the important part.

336
00:16:26,290 --> 00:16:28,350
‫As soon as we actually await the

337
00:16:28,350 --> 00:16:30,970
‫result of the query, so as soon as

338
00:16:30,970 --> 00:16:33,950
‫we use await here or here, for example.

339
00:16:33,950 --> 00:16:35,890
‫As soon as we use this await,

340
00:16:35,890 --> 00:16:37,910
‫the query will then execute and

341
00:16:37,910 --> 00:16:39,610
‫come back with the documents that

342
00:16:39,610 --> 00:16:42,144
‫actually match our query.

343
00:16:42,144 --> 00:16:44,960
‫If we do it like this, such as we have here,

344
00:16:44,960 --> 00:16:46,730
‫then there is now way of, later,

345
00:16:46,730 --> 00:16:49,110
‫implementing sorting, or pagination,

346
00:16:49,110 --> 00:16:50,793
‫or all of these other features.

347
00:16:51,880 --> 00:16:53,870
‫Instead, what we will have to do,

348
00:16:53,870 --> 00:16:57,220
‫is to save this part here into a query,

349
00:16:57,220 --> 00:17:00,200
‫then in the end, as soon as we change all the methods

350
00:17:00,200 --> 00:17:02,440
‫to the query that we need to, only then

351
00:17:02,440 --> 00:17:04,863
‫by the end, we can await that query.

352
00:17:06,080 --> 00:17:08,600
‫For example, we're going to use the sort method.

353
00:17:08,600 --> 00:17:10,200
‫We're going to use the predict method,

354
00:17:10,200 --> 00:17:12,440
‫we're going to use the limit method,

355
00:17:12,440 --> 00:17:14,500
‫and we're going to use, really, a bunch of methods,

356
00:17:14,500 --> 00:17:16,620
‫and chain them to this query.

357
00:17:16,620 --> 00:17:18,110
‫That would be impossible to do,

358
00:17:18,110 --> 00:17:20,910
‫again, if we await the result of

359
00:17:20,910 --> 00:17:23,073
‫this initial query here, right away.

360
00:17:24,590 --> 00:17:26,470
‫I hope that made sense.

361
00:17:26,470 --> 00:17:28,660
‫The way that we will do it

362
00:17:28,660 --> 00:17:30,140
‫is that we

363
00:17:31,090 --> 00:17:33,473
‫will have our tours down here.

364
00:17:35,540 --> 00:17:37,623
‫And this will await the query.

365
00:17:41,310 --> 00:17:43,830
‫The query is, well, simply the

366
00:17:43,830 --> 00:17:45,533
‫query without any await.

367
00:17:47,460 --> 00:17:49,360
‫Just to make it consistent with

368
00:17:49,360 --> 00:17:50,363
‫this part here,

369
00:17:52,060 --> 00:17:53,163
‫let's do it like this.

370
00:17:55,603 --> 00:17:57,123
‫Let's say that,

371
00:17:58,540 --> 00:18:00,437
‫first, we build the query

372
00:18:00,437 --> 00:18:03,363
‫and then we execute the query.

373
00:18:07,290 --> 00:18:08,313
‫That's not correct.

374
00:18:11,490 --> 00:18:13,040
‫Since we're doing comments here,

375
00:18:13,040 --> 00:18:14,330
‫let's also say send

376
00:18:15,300 --> 00:18:16,790
‫response.

377
00:18:16,790 --> 00:18:20,023
‫Just to make our code a bit more easy to scan.

378
00:18:20,870 --> 00:18:22,380
‫I hope that all of this made sense,

379
00:18:22,380 --> 00:18:24,820
‫this turned out to be quite a long video,

380
00:18:24,820 --> 00:18:26,780
‫but it was important to finish

381
00:18:26,780 --> 00:18:29,356
‫this part here by explaining you

382
00:18:29,356 --> 00:18:31,830
‫this logic here, so that in the next videos,

383
00:18:31,830 --> 00:18:34,080
‫we will then be able to implement

384
00:18:34,080 --> 00:18:36,110
‫the rest of the features.

385
00:18:36,110 --> 00:18:37,940
‫Because, again, without having it

386
00:18:37,940 --> 00:18:39,983
‫like this, it would not work.