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‫As the next feature in our API,

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‫we have field limiting,

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‫so, basically, in order to allow clients

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‫to choose which fields they want

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‫to get back in the response.

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‫So, for a client, it's always ideal

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‫to receive as little data as possible,

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‫in order to reduce the bandwidth

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‫that is consumed with each request.

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‫And that's, of course, especially true

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‫when we have really data-heavy data sets, right?

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‫And so it's a very nice feature

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‫to allow the API user to only request some of the fields.

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‫So, as the third feature, we will have field limiting.

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‫And, just like before, let me start by showing you

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‫how it's gonna work here in Postman.

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‫So, we're gonna specify a field called fields,

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‫and then the name of the fields

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‫that we actually want to receive.

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‫So let's say we only want the name,

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‫the duration,

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‫the difficulty, and the price, all right.

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‫And so, the implementation will actually be very similar

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‫to what we did before with sorting.

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‫So, if req.query.fields,

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‫then let's actually, again, create a variable

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‫for these fields here because just like before,

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‫Mongodbs, actually requests a string

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‫with the field name separated by spaces, all right?

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‫Now let me actually start by writing out

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‫that part, okay, so, the query itself.

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‫So query is equal to query.select, okay?

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‫And here, for example, it expects a string like,

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‫name then space, duration and a price for example, okay.

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‫And so this way, it will only select

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‫these three field names and send back

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‫the result only containing that, okay?

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‫And actually, this operation of selecting

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‫only certain field names is called projecting okay?

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‫So, let's now go ahead and create basically,

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‫the string, just like we did up there okay.

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‫So we start with req.query.fields,

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‫then we split it by a comma,

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‫and join it with an empty string.

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‫With a space actually, sorry.

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‫So with the space and so that's, then,

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‫gonna produce this exact string with this exact format.

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‫Then here, all we have to do is to use these fields.

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‫Then, just like before, I also want to add a default

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‫so in case the user does not specify the fields field,

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‫okay, so, in that case, we will just

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‫actually remove something, okay?

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‫And let me show that to you first, so down here,

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‫we always have this underscore underscore V,

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‫which is set to zero, and Mongodbs just creates these fields

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‫because it uses them internally.

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‫And we could disable them, but that's not a good practice.

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‫Again, because Mongodbs actually uses them, alright,

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‫but what we can do is to basically

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‫never send them to the client, so we can exclude them.

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‫And the way we do that is to, instead of doing

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‫underscore underscore V like before,

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‫so like we did up here, basically,

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‫we just prefix it with a minus, okay?

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‫And minus is then not including, but excluding.

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‫So what we had before here again,

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‫with the name and duration and price,

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‫that was to include these fields in the response.

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‫But this way, with the minus,

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‫we have everything except the V field here okay?

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‫So we're excluding only this field, alright?

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‫So let's go ahead and test that.

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‫Send it, and let's wait for it and yeah, indeed so,

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‫the ID is by default, always including okay?

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‫So we cannot remove that, but besides that,

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‫we have just the name, duration, difficulty, and price,

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‫okay, and we could, of course, also use that minus

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‫so that exclusion here as well.

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‫So we could have everything, minus the name

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‫and minus the duration, for example.

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‫So let's test that as well.

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‫And so, if you now check it, you will not see the name,

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‫and not see the duration anywhere here.

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‫Right, and now just as a final test,

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‫let's see if our default works as well.

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‫Sending the response and so, now we no longer have

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‫that V variable here set to zero in all the documents.

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‫All right, great, now there's one last thing

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‫that I want to show you which is that

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‫we can also exclude fields right from the schema.

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‫Alright, and that can be very useful,

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‫for example, when we have sensitive data

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‫that should only be used internally.

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‫For example, stuff like passwords

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‫should never be exposed to the client

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‫and so therefore, we can exclude

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‫some fields right in the schema.

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‫So for example, we might not want the user

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‫to see when exactly each tour was created.

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‫For example, tour might already be

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‫kind of old or something and so,

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‫let's say we want to always hide this createdAt field,

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‫alright, so we can go into our schema,

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‫which is in the tour model of course,

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‫and then at createdAt, we simply set

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‫the select property here to false.

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‫And now when we try to get our results,

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‫you see that it's actually no longer there okay?

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‫And so like this, we can basically,

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‫permanently hide this from the output.

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‫Perfect, so one more feature that is actually working now

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‫and so let's now move on right to the next one.