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Now that we implemented our MongoDB logic,

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let's wrap up this course section

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by adding some error handling to the API routes.

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Because data is also something you should know how to do.

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When you run server side code,

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things don't always go right.

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And at the moment we assume that everything works.

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Like here.

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When we store a newsletter.

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When we do that,

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we check the request method,

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check that it's a post method.

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And if it is, we basically just validate the input.

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That's one case

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where we send back an error status code if it's not valid.

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But for working with the database we just assume that

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everything works.

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And that's unrealistic.

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Things won't always work.

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Connecting to the database could fail

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or even if we are connected,

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inserting data could fail for whatever reason.

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Because the database servers went down temporarily

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just when we tried to insert data.

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Things can fail.

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No matter how unlikely that might be.

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So how do we deal with that then?

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Well, since I'm using a single weight here,

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we can use, try catch

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to try certain operations, catch errors

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and then send back a response if things go wrong.

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And here I actually wanna work with

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two different try catch blocks.

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I wanna try connecting.

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And if that fails, I wanna send back an error.

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But if it succeeds, I want to try this code.

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So inserting, I wanna try that.

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And if that fails,

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I want to send back an error,

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a different error.

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And I then also still wanna close the open connection.

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And to do this in an elegant way

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I'll work with some helper functions.

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For that I'll add a new function,

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which will name, connect database.

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The name is up to you of course.

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And this function here,

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will just hold this code for establishing a connection.

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So I'll put that in here,

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and then just return the client.

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And I'll add another of function,

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which I'll name, insert document,

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where I expect to get access to the client.

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And where I get the document that should

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be inserted as parameters.

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And inside of insert document,

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I then wanna run this code here.

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So copy that into insert document.

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And of course in order to use a weight

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there should be an async function

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and this here should be an async function as well.

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Connected database.

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Now, with that done down here in our main handler function,

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I get the client by calling connect database

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and then I will call insert document,

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pass my client as a first argument.

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And that document here as a second argument.

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Now I wanna await connect database

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because it is a async function

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so it returns a promise

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and we need to wait for disconnection to be established.

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And for the same reason

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we also want to await inserted document

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because that's also an async operation.

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Now with that outsourced to make this code

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a bit more readable,

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I will wrap connecting

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with try and catch potential errors here.

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And I'll then do the same for inserting here.

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I'll also wrap this with try and catch errors here.

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Now I wanna call a client close

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if we did connect successfully,

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but we failed to insert.

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So I wanna call client close instead

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of this try block here as well.

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And to make sure that client is available here,

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I'll set it as a variable here,

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and set it to a value in the first try block.

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And if we make it past this block,

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client will be the connected database.

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So calling close will work then.

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And then here we got the different errors.

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If we fail to connect,

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I wanna send back a response

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where I set the status code to 500.

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Which indicates that something went wrong on this server.

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Which clearly is the case here.

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And I'll send back a object as json

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which has a message where I say,

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connecting to the database failed.

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And if that failed,

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I don't wanna continue with the other code.

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I don't want to continue with this try-catch block.

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And I certainly don't want to send back this response.

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Eventually,

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hence here all returned in

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to prevent fervor function execution.

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I'll do something similar here if we fail to insert.

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I'll copy that code

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but I'll set the message to, inserting data failed.

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And that's how we can handle errors here.

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If we make it past both try-catch blocks.

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So if we don't go into any of these catch blocks,

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to be precise,

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we will still send back that success response.

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Now to check whatever didn't works.

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We can temporarily break disconnect database function

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by using incorrect credentials

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like a username that doesn't exist.

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We save that

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and I go back to the newsletter part here.

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If I try to sign up with some dummy newsletter

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we see that we get back an error here,

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in the network tab we also see it.

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We see that we got back a response

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with a status code of 500

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where the message we get is connecting

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to the database failed.

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Now, as mentioned before, we don't have any feedback

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on the user interface and you might of course

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want to add such feedback also

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for the loading states and on.

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I just didn't focus on this at the moment

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because I want to thoroughly dive into API routes.

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And there we can see that our error handling works.

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If I go back to a correct username

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and we try that same request again,

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I still get an error.

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Inserting data failed is what I get now.

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That's unintended but it's good to know.

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Let's see what went wrong there.

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And the problem here is a simple error I made

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in this extra inserts document function.

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I'm accepting client and document,

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while, I should be using that document

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for inserting data.

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Instead of having my hard coded document there

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as I had before

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where I referenced user email,

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which is just not available

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I should be using the document we get as a parameter.

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So still nice to see that this error handling also worked.

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But with that fixed,

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if we now try this again.

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Now that's looking better.

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We got a success response here and it works.

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So that's how we can add error handling here.

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Now let's also add it to the other API route.