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So here I am connected to that mongodb Atlas server in the web

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and I will use a new database,

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blog and in there, let's quickly insert some dummy data.

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Let's insert a users collection and I'll insert one user here,

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I'll make this really simple,

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I'll have a user with the name of Max. That is my one user,

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now I got a user ID and I will copy that ID because now I'll add a posts collection where I insert many

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posts, therefore I need an array here

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and then the first post has a title of first post and important, a user ID at which it points,

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so here I'll use a relation with references.

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Check out the relations module in this course if you want to learn more about data schemas and relations.

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So here I'll just store that ID and then I'll add a second post here with a title of second post and

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that post will have been created by the same user,

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so I store the same ID as a value here.

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If I hit enter, these two posts are also created.

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Now if we want to delete the user, we would obviously find out the user id and that is probably something

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you know in the application where the user clicked on delete my account,

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so in the end you would do something like db users delete one and then search for _id equal

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to that user ID which you know. Now you would do that

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and then with that user ID which you do know, you would of course also go ahead and also execute db

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products delete many and delete all products where the user ID,

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so that field which I added to each post where we point at the user is equal to the user id too.

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I won't execute these commands because I don't want to delete the data right now but this is how we

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could clear all the data and this would work in 99.9%

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of cases. The problem just is the cases where it doesn't work because something goes wrong and

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we end up in a state where it suddenly, well we deleted the user but not the posts or the other way around

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and for that, we can work with transactions.

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Now how does a transaction work?

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Let's dive into that in the next lecture.