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In the last lecture, I gave you a hint that there is this language, this templating language we can use

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here to extract data from the request we have and define which data we want to forward.

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Now actually, you can learn more about this language if you Google for AWS API Gateway body mapping

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templates.

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The first article you find here below the ads gives you an overview over this language,

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the special variables you can use in this body mapping template text box there and how you can retrieve

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data. This is a good place to dive deeper

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but you'll also see quite some examples throughout this course.

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A quick example can be found if you go to the drop-down and choose method request pass through.

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What this does is it gives you a quite elaborate template, you might not understand all of that I can

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tell you it uses Apache's Velocity language and it basically extracts a lot of data from the request,

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data from the request body

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but also a lot of metadata.

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If we save this and I will come back to explaining this later and we go back to testing this, you will

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still see null because our lambda code still tries to access an age property which doesn't exist on event

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but if we go to our cloud watch logs here and we wait for the latest log to arrive, you will see that

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now we log a big object which has a body JSON property which holds our actual request body,

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now not as a JSON string but already as a Javascript object,

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all of this is a Javascript object and a lot of other information about this request. So kind of similar

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to the time we use this checkbox, use this proxy integration and forward everything

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but now not forwarding the request but forwarding a mapped template or a mapped event data object with

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data from that request which is also the reason why we wouldn't have to parse JSON data here because

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it already is a mapped Javascript object instead

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and that's the power.

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Also, this doesn't override our integration response,

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we're still in the world of API Gateway doing the request and response handling,

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we just happen to extract a lot of data from the request and pass it to the action

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but we can narrow this down.

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We can go to our template and get rid of all the stuff at the bottom here,

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a lot of information we don't need about authorization and so on, we'll need this later though and only extract

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data from the request body

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and this is done with this special command, input JSON and then dollar sign.

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This is dollar sign, a special variable which refers to your request body and JSON simply parses

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it and with that, you can also of course rename this to age and not parse your full request body but there,

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person data, you know that is a property on the request body you're parsing and then age. And now if

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we remove this comma, important that you don't have a syntax error,

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now if we save this and go back to testing this, if we hit test here, you'll see 56 again

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and important too if you check your cloud watch logs, wait for the latest one to arrive

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again, you'll see that we only received this object.

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So all the other data was dropped,

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we have no other metadata about the requests because in our mapping template under integration request

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here, we only extract that

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and the difficult part here to grasp probably is the language we use with this $input.json('$')

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thing.

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So let's dive deeper into this in the next lecture.