API gateway body mapper nested objects - amazon-dynamodb

Question

I have an endpoint setup on API gateway that is talking directly to DynamoDB.
As a post request comes in I use the body mapper script to map my url request parameters to dynamoDB params.
My URL params
{
"name": "sdaf",
"location": "asdf",
"gender": "male"
}
Body Mapper Script
{
"TableName": "sample-table",
"Item": {
"firstName": {
"S": "$input.path('$.name')"
},
"location": {
"S": "$input.path('$.location')"
}
}
}
All of this works fine until I have to write a whole object to dynamo.
New URL Params
{
"name": "sdaf",
"location": "asdf",
"gender": "male",
"hobbies": {
"hobby1": {
"startedAt": "<some time>"
},
"hobby2": {
"startedAt": "<some time>"
},
}
}
I am not sure how the body mapper is supposed to look like for this situation?
I have tried this:
Body Mapper
{
"TableName": "sample-table",
"Item": {
"firstName": {
"S": "$input.path('$.name')"
},
"location": {
"S": "$input.path('$.location')"
},
"hobbies": {
"M": "$input.path('$.hobbies')"
}
}
}
But doesn't work. I wonder if there is a way to dump an object into a column in dynamo from the api gateway directly. I know this is possible with adding a lambda in between but I want to avoid that.

Answer 1

I don't think this can be made to work while passing hobbies as a URL parameter.
If you instead pass hobbies in the body, you can do something like this:
"M": {
#foreach( $elem in $input.path('$.hobbies'))
$elem
#if($foreach.hasNext),#end
#end
}