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In the last lecture, we added a model and we used it for validating incoming requests bodies.

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Now I just want to highlight it again even though I said it before, this is optional,

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the whole idea of using models is optional and of course, you don't have to do validation of incoming

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bodies or you could also validate headers and so on here, you could implement the same logic in lambda.

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So if you pass data from your request body to lambda,

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since you use a normal programming language like Javascript in lambda, you could of course also do the

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validation lambda,

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you could simply validate there if the requests body holds an age property

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and if that age property holds a valid integer, that could be done there.

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The idea of using a model for that and using this built-in validator API Gateway offers you simply

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is to give you an easier way of adding such implementation.

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You get an out-of-the-box working implementation of validation which returns an error if it fails and

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that can be very convenient

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but again, it's optional.

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Now validation of incoming requests is not everything you can do with models.

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You can also use models to map data or you can use them in general in this mapping process I should say,

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so how does this work?

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Let's go back to our main page with all these boxes and let's go back to the integration request box

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which is all about transforming data and forwarding it to the action, to the lambda function here

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in the end. There if you have a look at our current body mapping template, we see that right now, we're still

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accessing a person data object on the request body and there on that person data object, we tried

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to access an age property.

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Now clearly, we don't have that because we have a model in place which makes sure that since we use validation,

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only an object with age, height and income reaches our back-end you could say. Therefore there is no chance

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of a person data property being valid or being there on this object,

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so hence this current type of data extraction doesn't really make a whole lot of sense.

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So what we can do instead is on this body mapping template, we can simply extract age like that,

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right because we know on that request body, there will be an age property because that is what we're

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validating for.

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Now if we had a more complex model and we're not really interested in all the data we get, we don't want

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to pass all that data which is part of our model to lambda,

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we could also use a different way of generating this template. Here on this drop-down next to generate

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template,

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you see you can select from all the models you have set up.

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There are the two default models API Gateway gives you out-of-the-box and there's our compare data model.

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Now if we click this, we see that we get this template generated for us and what's happening there is

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that in the first line with this set call, we simply set our own variable which we can use inside of

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this template,

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the inputRoot variable, this is a variable which you could of course also rename,

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that's no reserved name and what it does here is it simply extracts the request

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body with this path method here.

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Before we used $input.json ('$'),

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well now we're using path in the end here,

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this will give us the same,

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it will give us access to our request body. So inputRoot is our whole request body and therefore, we

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could of course map a custom age variable to $inputRoot.age and maybe omit the other two if we don't want

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to pass them to lambda.

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So now we will make sure that lambda only gets an age property which holds, well the value of our actual

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age property we have on the request body.

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And of course, this is kind of a constructed example,

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there are also more useful cases where you again, have more structured, more complex data reaching your

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back-end and you want to extract the data and then again, you can conveniently map that against your

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model with this little helper which does some set up for you.

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Now if we save this, we should see that if we test it again, so we go back to test on the client here

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and we submit data, so we have our age field, 28,

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then we have our height

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field, 72, and keep in mind, you need all these fields because we still have validation in place,

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so even though we don't forward them all to lambda, we still need them all, income could be 3000,

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whatever

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and now hit test and you should see that your age which we're getting back is again 56.

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So it seems to work that we pass age to lambda, even though we cut the two fields, income and height

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we're not interested in. Now just as we can use this little helper of creating a mapping template for integration

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request, we can do the same for integration response.

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So let's go there and let's open the body mapping template of our example

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response here. If we have a look at it, right now we're returning this your age property where we simply

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output whatever lambda returns to us.

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Now we can of course also generate a template here based on our compare data and it does the same

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as before,

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it accesses whatever

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in this case lambda returns to us with $input.path ('$') and maps it to our inputRoot

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variable.

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Now we can use this inputRoot variable here and we could therefore again create a your age property and

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simply set this equal to inputRoot,

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this time not .age because inputRoot

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keep in mind is here whatever lambda returns to us

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and if you have a look at our function, you of course see that lambda still only returns the age times two,

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so it returns a number.

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So with that, we can also cut the other two properties here,

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we could also set them to null or to some other default values if we'd like to and hit save here.

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And with that, we should see the same behavior as before but now again using this generate template helper

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and again, this is super useful if you've got a more complex model and want to quickly generate a template

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which incorporates it.

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This is something I want to show you too, again just as everything else connected to models,

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this is optional,

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you don't have to use models but if you want to use them, they offer some nice benefits, validation, this

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easy mapping here.

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So I'd say it's time to practice them in the next assignment.