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I am connected to a running mongod instance again and I'll use a dataset which we prepared in the insert

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module, in case you skipped that, you find it attached,

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you just need to import it into a new collection and database. It is this users dataset with a couple

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of users in there.

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Now here, I got some nice data and since this is the update module, now everything is about changing that

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data

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and let's start with Chris because Chris does not look like the other entries, the hobbies there are different,

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there is no age,

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there is no phone number,

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so this is a perfect use case to update this data piece

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and of course you would not just update from inside the shell,

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it's of course typical that you build an application, let's say a blog where your users can edit a blog

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post and once they hit save, you want to reflect that save in a database of course.

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So how can we update Chris?

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Well, an update operation requires two pieces of information, we need to be able to identify the document

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that should be changed and then we need to define how it should change. For identification,

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you can use any filter

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you could also use for finding documents.

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You don't have to use the ID,

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you can find Chris by his name, by the hobbies, by a combination of name and hobbies,

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this is all possible and you can also not just update one document at a time. If we want to update Chris,

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I'll do it by ID which is a common scenario but as I just mentioned, not a must do, if I want to update

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Chris,

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I'll have a look at my persons

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and there, I can use updateOne just like with insert one and insert many,

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we have update one an update many and the names are pretty self-explanatory.

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Update one simply takes the first document that matches your filter criteria and updates that even if

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multiple documents would normally match your criteria,

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update many will take your criteria, your filter and update all documents that match it.

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So here I have update one,

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now I add my filter criteria and I say ID should be equal to that objectid and then the second argument

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in the update method is basically some information on how to update this object

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and there you can use a variety of update operators.

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Now you can find all update operators in the official docs in the reference under update operators

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and I will walk you through the most important ones in this module of course.

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Right now we're here in the field

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update operators because I want to update a field or a couple of fields actually.

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Now for that, we use $set

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and we saw that earlier in the course already. $set simply takes a document where you describe

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some fields that should be changed or added to the existing document,

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so here I could say that I want to change hobbies,

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hobbies already exists and it is an array and we have specific operators for working with arrays

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but if I just want to completely override hobbies which is what I want to do here, I can use it here

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together with set and then I simply define the new value for hobbies and this should still be an array,

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hence the square brackets,

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this will not add these elements to the existing array though, it will simply override the existing

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hobbies.

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So now I will look at a couple of documents in the array where each document has a title and then we

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have sports and then a frequency like five, let's say, Chris is really sporty and then we add another document

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and now these are really just the documents that will be inside the hobbies array.

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So there we have another hobby with a title of cooking and a frequency of three let's say and then

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we have a last document in that array where we have a title of hiking

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and then we have a frequency of one. If I now hit enter, I get an error

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because the collection is not called persons but users,

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sorry about that

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and I have a typo so I also should fix that,

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it's of course update one, so little typo in there. The arguments there, that is all correct,

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nothing needs to change there.

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If I hit enter, we now get a feedback that it found one matching document,

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so for our filter, this one, it found one matching document and it also modified one document because

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the changes which we defined here made sense.

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And with that I mean that if I would run this again, the exact same command, I actually still have a matched

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count because we still have a matching document for the ID, the ID didn't change but it didn't modify

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anything because the one change that I instructed here didn't make sense,

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so mongodb ignored it because the value I wanted to set here is the already existing value.

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Now it's also interesting to see that if I now find all users, that Chris still has his name and the ID,

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so $set does not override the existing values

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instead it simply just defines some changes that mongodb evaluates and then if they make sense,

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it changes the existing document by adding or overriding these fields. All the existing fields are left

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untouched,

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they are not removed.

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You can remove fields and I'll come to that in this module but by default, it simply just adds or edits

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the fields which you specify,

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so this is update one.

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Now of course you're not limited to update one,

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you could update many

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and for that, I will find users who have and for that, let's quickly look into users who have a hobby with

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title sports.

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So let me quickly search for hobbies.title, that is how you can search for embedded documents in an

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array and that should be equal to sports, close the

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quotation marks, output this in a pretty way and you see we have Anna, Max and Chris.

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Now let's say all persons who have that hobby should receive a new field which says isSporty

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true,

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so where I set a boolean value to true for a newly added field.

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Now since I have three documents that should be updated, I could of course do it with update one three times

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and manually search the ID here with the find method, copy the ID, execute update one or I take the simpler

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route and simply replace find with update many and the filter stays the same and the second argument

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then defines the change that should be applied to every document

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and here again, I use $set to then set a new field which didn't exist before, isSporty to

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true

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and that is all.

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If I now hit enter,

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you see it found three documents and it modified three documents and if I now quickly search all users,

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you'll see that Chris has isSporty true, Anna has isSporty true and Manuel does not have it because

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there is no sports as a hobby and Max does have isSporty

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true.

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So this is now all set

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with the help of update many and that's update one and update many and $set.