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In this video.

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Let's see how we can handle saying errors in experts, for example, when dealing with databases.

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Because of that, we are going to handle some possible errors when working with MongoDB, for example,

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validation errors, duplicate key errors and invalid object ID errors, even though Mongoose handles

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these errors for us automatically.

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But what we want to do is that we want to send some meaningful messages to the end user.

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So let's start it inside the config folder.

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We have a file that connect to MongoDB and you can see that I am calling the function automatically

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here and without exporting it.

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So as soon as I require this file, this function will run.

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And inside the model we have one file called Postal JS and on that we have post schema and inside the

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schema we have to file title and content and these fields are required.

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Field.

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So next step is let's go ahead to require the function to connect to MongoDB.

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So back to the server file.

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Let's go ahead and do that.

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I have collapse or the route that we are done with it.

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So above here, this is how I'm going to require the file to connect to MongoDB.

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And make sure that your server is running.

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So let's check it out and you can see that it has been connected to MongoDB.

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The next step is let's require the model const posts is equal to required for a PS+ model and then the

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posts.

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So let's create a route to create post.

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So here we're going to be the end point post for a slash post.

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So here we go, app dot post, forward slash post, and then the handler requests response and my error

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function and let me mark my function as an async.

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So insert here I will bring in try and catch inside a patch.

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Let's send the error message.

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And instead of try, let's go ahead and create the post.

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I'll pass in the entire request, buddy.

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And here we go.

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To be able to receive incoming data from experts.

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We need to configure it by making use of upload to use and then Xpress dot Jason and that is it.

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So let's go ahead and send the response if everything goes on well.

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So let's go ahead and make the request.

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And I'm going to use this extension called ten lines.

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This is a route and then you're going to be the post mortem.

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So when I hit ST with that passing in the title and the contents, let's look at the arrow.

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Now this is what we have.

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Looking at the structure of this arrow is not all that descriptive to the end user.

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You can see we have nested objects before we can even get an actual message.

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So our job is that we are going to handle this error and display some meaningful error messages.

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Remember, we have created the Arrow class here.

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So any time we want to send some meaningful error messages, we are going to pass the arrow to this

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arrow class.

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So inside the cards we are going to use the error class or the function that we have created.

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Because of that, we need to pass in another element called Next because we are going to pass the error

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to next.

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So inside here we are going to avoid using this way, but instead we are going to call next and remember

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next accept the structured error, which is from the up arrow.

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So because of that, our make use of new and then our code, the app error.

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And here the first element is the error that we want to send.

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And that error can be found on this object.

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So here our pass in the entire error here.

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And then this is code 400.

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So with this one, let's look at the structure.

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Now, when I hit Saint and you can see that this message is clear than the previous one better so we

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can create its own function to have well-structured message than this one because this error that we

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pass in is a global error.

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But we can create a specific function to handle this kind of error.

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For example, validation error as we've seen.

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So the takeaway here is that if you want to handle async error, you need to bring it next here and

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then inside a catch you pass in the entire error to the app error class.

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Or we can create a global function where we are going to take away the catch.

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And so any time I want to cut any error, I don't want to bring in here, but instead I will wrap the

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entire function inside this global catch error handler.

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But to make it more simple, let's maintain in this way.

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So this is how we can handle async error in express in the next video.

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Let's go ahead and improve the way we are sending error, such as the validation error to the end user.