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Now that we added some data into our database in the last lecture,

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let's come back to that json thing because actually, mongodb does not use json but bson on which

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stands for binary json for storing data in your database.

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Now you don't really need to care too much about that because all you will write and see will be json code like

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we did it,

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so this is json code,

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this is what we use in the last lecture,

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this is also what we see when we retrieve data from mongodb

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but behind the scenes, mongodb actually uses bson data.

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This conversion is done by the drivers,

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so this basically takes your json code and stores it in binary data

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and this is simply done because for one, it is more efficient to store than json data, so it's faster

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and more efficient from a space, from a size perspective

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and additionally it supports additional types because for example that objectId thing we saw in the

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last lecture is not valid normal

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json. If I were to go in to my editor which is visual studio code which you don't need but this is

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simply an editor you can use for coding

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and I would manually add an ID field here

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and set this equal to type objectId with some text in there,

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you see that my editor doesn't like this because it's not valid

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json. Now it is not valid

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json but mongodb can actually understand and take this and store it in its binary data

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and there are some other types too

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like for example you got different types of numbers with decimals and very big numbers

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and these are stored in different ways

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behind the scenes, you don't need to care too much about that

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but this is something mongodb offers you, this special data type, other special data types and very

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efficient storage

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in general. We will always work with our data like this though,

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so in json format and there's one other important thing you need to understand about this data.

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If I add another piece of information into flight data with insert one,

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so if I add another document and this time I'll type it manually, when adding data like this,

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you can actually omit the quotation marks here as long as there is no whitespace in the name.

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So we could also have departure airport like this and this would still be accepted so I don't need

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to wrap the name into quotation marks here,

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you can still do it to be very clear that this is json but well we know it's json, you can use it

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like this as a shortcut, the value if it's a string still needs to be enclosed in double quotation marks though.

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So if we had Berlin Tegel as an airport here and then let's say we have the arrival airport which

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is heathrow,

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then we could write it like this.

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We can now also theoretically save it like this even though the aircraft, the distance and the information

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whether this is an intercontinental flight is missing because you can have mixed documents in the same

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collection. If you add the data like this, you still see, this is accepted

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and if I now access all my flight data and find it and pretty print it, you'll see both documents exist

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in there even though they have different schemas.

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Now we'll dive a bit deeper into schema design and how we should structure our data in a separate module

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but I also want you to take away and keep in mind that in mongodb, two documents in the same collection

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don't have to have the same schema.

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Often you will have at least some intersections or complete the equal schemas but it's not a must.

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One other thing you have to know is that this ID which is auto-generated, you don't have to use

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the auto-generated ID, you just have to ensure that you have a unique ID

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but if you can ensure this, you can also assign IDs on your own. So if I add this same entry again with

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departure airport and arrival airport,

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I can add _ID in there as an extra field and it has to be _ID,

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so not just ID, also not ID with a capital character, _id like this

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and then you can use any ID you want, a number or

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another string like txl-lhr-1. This can be done and you see this was also accepted

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and inserted with this ID,

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so if I again print all the results here, you see we got our two old results and this new one and this

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new one does now not have an objectId which was generated for us by mongodb but our own ID. If

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I try to enter the same entry again with the same ID though and that's the only thing which is the

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problem here, not the other data,

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the other data maybe equal as you can see here but if I use the same id again, we get an error

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and in the end, this error is simply telling us that we get a duplicate key error in this collection

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and that the duplicate key is the ID which is not allowed.

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So this is the error we're seeing here and this is something you should also pay close attention to.