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We've worked with our flight data quite a bit,

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now let me add another kind of data. I'll clear the console with the cls command for that

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and now I'll add a passenger's collection to my flight's database

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and I want to insertMany passengers in there. Now you find a file attached to this video, the

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passengers.json file with an array of passenger data,

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just some dummy names and ages.

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Copy that and add it here and add a closing parentheses at the end and hit enter

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and this should insert many elements with the insertMany command with all these automatically generated

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IDs.

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Now we can have a look at that data by accessing passengers and you can always just type and then use

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tab auto-completion here by the way, so simply hit tab in the shell

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and it should auto-complete, you can find them and pretty print the results,

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there are our passengers. Now on first sight, this might look good but actually if you have a look at the

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last entry, Albert Twostone and then you have a look at the data you found attached,

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you will see that Albert is not the last entry,

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Gordon Black actually is. Now the order

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here is the same order as it was added to the database,

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so where is Gordon?

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Well you also see the type it for more,

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if we type it, then we see Gordon Black.

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Now this it command is a feature shown in the shell,

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I will show you another way of getting the data

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if you were using a mongodb driver in an application in a second

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but the fact that we had used that is not shell specific, instead find,

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so passengers find or the find command in general no matter on which collection you use it gives you

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back a cursor

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and not all the data.

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Previously, it looked like it always gives us back all the data

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but actually it gives us a so-called cursor object,

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now what is that? Find does not give us an array of all the documents in a collection and that makes

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a lot of sense because that collection could be very big

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and if find would immediately send us back all documents and you think about a collection with let's

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say 20 million documents, then this would take super long but most importantly, it would send a lot of

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data over the wire,

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so instead of that, it gives us back cursor object which is an object with a lot of metadata behind it that

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allows us to cycle through the results

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and that is what that it command did,

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it basically used that cursor to fetch the next bunch of data.

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So find here really just gives us back that cursor and we can actually see that by using some other methods

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here,

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for example there is toArray,

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if you execute this, now you see Gordon Black as the last element

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and now there is no type it to see more

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because toArray will actually go ahead and exhaust the cursor,

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so go through the entire list and fetch all the documents and not stop after the first 20, which by the way

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is simply a feature by the mongodb shell,

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it gives you the first 20 documents automatically but then stops, toArray simply gets them all and gives

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you an array.

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Now that might be fine here but of course that is also not optimal if you've got a lot of elements. In

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your application code, you would most likely use something like passengers find

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and then there is a forEach method and forEach here simply allows you to write some code to do something

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on every element that is in your database, on every document you got in there.

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Now the exact syntax you can use is something you can find in the driver docs for your driver,

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so if you're using PHP, check out the PHP mongodb driver docs and you will see how to use that

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forEach function. In javascript and the shell is based on javascript,

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you could pass a javascript function to it using an arrow function here where you will get an argument

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passed into the function automatically and that will be your document and you can name this argument

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however you want,

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so in our case it will be our passenger data

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and then you can use it in here and here in the shell, there is a print json command which we can use

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to pass or to well yeah pass our json data which we want to output like passenger data.

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And now we also get all the documents because now what we're doing is on the cursor which find does

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return, we execute the built-in forEach method to execute this method here,

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this anonymous method on every element and the cursor will simply go through our entire collection,

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fetch all documents one at a time, execute that function on it, pass the document into the function

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and then here we just happened to print it out like this in your application with your favorite language.

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You can of course do to the data whatever you want to do, render it onto a html page, send it with an

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http request, whatever you need to do

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and that is just what I want you to take away from this lecture.

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Find does not by default give you all the documents even though it looked like it did because the shell

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actually gives you the first 20 documents by default,

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instead find gives you a cursor and then it's up to you to use that cursor with toArray to force it

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to get all documents and put them into an array or better for large sets of documents, with forEach

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and there are more methods available which you find in your driver docs.

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Technically you need to know that with forEach, it will really just fetch the next document for every loop

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cycle,

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so this is very efficient here because it does not fetch all the data in advance, load it into memory

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and then force you to go through it with forEach, instead it really just fetches the data on the demand

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therefore of course not overusing your bandwidth and not loading too much into memory.

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So this is the important thing to take away,

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find gives you a cursor and not the element itself.

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This also is the reason why on find one, we could not use pretty, you remember if I use passengers find

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one, this works, find one pretty fails because pretty is a method that simply exists on the cursor here.

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So this is why find one does not support it

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because find one does not give us a cursor because it only gives us one document anyways.

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Find gives us multiple documents,

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therefore we don't get the data immediately,

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we get the cursor instead, the shell happens to take that cursor and give us the first 20 documents by default

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but we can also control that with forEach or toArray

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and here, pretty exists because it is simply a method that exists on the cursor to pretty print the output.

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This is what you need to take away here, for the other methods like insert, update and delete, cursors

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do not exist because these methods don't fetch data,

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they manipulate it

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instead.