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So we want to add validation

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and actually I want to use my posts example here.

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Now how can you add validation in mongodb?

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A very easy way of adding it is when you add a collection for the first time,

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so when you create a collection and you learned that the collection is created automatically when you

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start inserting data into it.

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So here let's say I want to drop my posts collection,

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so now if I try to find one post, that will not work.

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Now let's create the collection differently, not implicitly once we add something but explicitly. For

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that we got the create collection command,

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we didn't use it thus far because often that lazy creation where it only gets created if it's needed

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is ok but if you want to configure your collection in a special way,

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well then you can use that create collection command.

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There you first of all as a first argument to the create collection method define the name of the collection and

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in our case, that would be posts, so previously you just accessed it and started working with it,

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now you create it and therefore you have to define the name here.

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The second argument is a document where you can configure that collection

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and one important piece of configuration here is the validator.

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The validator key takes another sub-document where you can now define a schema against which incoming

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data with insert or with inserts or updates has to validate.

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You do this by adding a json schema key,

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$jsonschema key here,

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$jsonschema

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and then again another nested document and this now holds the schema.

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So here we're just saying hey our validator is the json schema,

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historically there were other validators but it is strongly recommended to go with json schema now and

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then you define the schema here in this nested document.

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Now there you can define a schema for every document which is added to the collection,

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for example we can set the bson type here to object,

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so everything that gets added to the collection should be a valid document or object.

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More interestingly, we can set a required key here which is an array and here, we can define names of

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fields in the document which will be part of that post collection that are absolutely required and if

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we try to add data that does not have these fields, we'll get an error or warning depending on our settings.

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So here, we simply pass the names of the fields like in our case for the post here, you could say a title is

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required and a text is required,

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maybe tags are not required.

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The creator is required though,

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so creator and the comments let's say are also required.

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So now these four fields are required on every document that gets added to the post collection.

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Now we can even dive a bit deeper and start working on our properties,

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now since this actually gets a bit hard to read,

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let me actually take the entire command here and move into a text editor where that is easier to read.

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I created a validation.js file,

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it should be a js file

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if you're using a tool like visual studio code to get nice syntax completion,

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the name does not matter at all and I'll paste in my command and use the auto formatting capabilities

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of that IDE which you can find by inspecting the keybindings there under preferences keyboard shortcuts

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and then format documents is what you want to look for, this shortcut here

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I use that to format this in a nicer way.

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So this is what you wrote thus far, a validator with a schema for the overall document

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and now we can add a properties key which is another nested document where we can define for every property

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of every document that gets added to the post collection, how it should look like,

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for example the title field.

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Keep in mind, the title is required here, by the way

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that is incorrect,

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every element here should be a separate string, not one big string, so like this, it should look like this

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for strings. So title is required

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and now we can define it in even more detail,

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we can not just say it's required which is already done here,

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we can say the bson type here should be string and that comes back to the data types you learned before

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and also consult that lecture I added earlier where you see a list of all the data types because you'll

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need the type as it's noted in the mongodb documentation here,

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so only strings are accepted as titles. You can also add a description here, so it must be a string and is required

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could be added here. And we can do that

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for all our properties now,

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so for the text too, what would that be?

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Well it would also be a string and we can also pass a description here which is just the same description

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as up there.

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The creator on the other hand,

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that would be a bson type of objectId

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and here the mongodb equivalent is objectId written this as a string,

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so here we can also add this must be an objectId and is required.

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We also have our comments here and the comment has a bson type of array because in our post, we got

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multiple comments so we can also add a description,

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must be an array and of course our comments since we have multiple items in there, you can an add items key here

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which describes how the items should look like in that array.

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There you can set the bson type to object because every item will have to be a document, it's not allowed

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to be a string, it will have to be a document.

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Well and in our comments, as we added them before, we had a text and an author, so we'll again add a properties

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key here and now basically say well every item in an array has a text field which in turn is of type

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or bson type text where we can have description must be a string and is required and for it to be

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required on the items in the array, we should add the required key and say that text is required

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and that author is required

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and then down there in the properties set up, we can also add or we should add the author and say well

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the author, here the bson type is objectId and we also have a description must be an objectId and

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is required.

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Now you can find this document attached to this video in case this was too fast,

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in the end I'm defining a simple schema on how you can validate incoming data for our posts collection

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and I'm doing this when we create the collection, so we can copy that entire command now and move back

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to the shell

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and of course at the end of this module, you'll find a link to the detailed official docs with all validation

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options.

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So I can enter this command here and I got an error here, objectid is not understood

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and indeed that is correct,

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it should be objectId with a capital I, in the file which you download this will already be fixed.

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I fix it here manually and I also had a problem here, the bson type of text is not text but string,

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I did that correctly up here,

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simply reuse text here,

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that should be string. Again in the document you download this will be fixed. With that added,

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let's now add it here, we get

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ok

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and now if I look at the posts, there's nothing in there of course still

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but now let's insert a document.

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And for that, I'll repeat my previous insertion with title my first post, text and so on,

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if I hit enter, this succeeds,

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so now if I find one post,

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this is the post I added.

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Now let me try inserting something where my author is not an objectId let's say but a random number

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because maybe I have authors stored which I want to match by that number which fits another field.

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Now I get an error, I get an error in the end which says document failed validation and that is a pretty

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clear error

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right,

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we failed validation

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and if I now look into my posts with find to see all posts in there, we actually see indeed

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the post was not added there because we just get an error telling us that we failed.