How to use openWhisk forwarder combinator to forward parameters around a cloudant action - openwhisk

Question

I have this scenario where I want to check if user's email is already been used when trying to signup and throw an error “user already exists” in that case.
here’s what my sequence looks like:
Input action -> CloudnAnt EXE QUERY-Find -> Validate email action -> CloudnAnt create User/Throw user already exists error action
my json payload looks like this :
{email: 'blahblah#domain.com', pass: "pass"}
the problem is that I have no control over the output of the cloudnant predefined actions, and by that I lose the payload after the 2nd action "CloudnAnt EXE QUERY-Find User with email action"
Is there a way to keep my input all the way through the sequence? and could the forward combinator be the solution for this issue?

Answer 1

I'd try /whisk.system/combinators/forwarder, which lets you pass arguments to an action and then specify arguments that get sent to the next one. Ie, I've got 5 arguments, let's pass 1 and 2 on to the next item in the sequence, and when done, pass 3, 4, 5 to the next one. I believe the output from the first item goes along as well.

Answer 2

The solution is very simple, just replace the cloudant action with a forward combinator which will invoke the cloudant action and forward the parameters around it.
to invoke a cloudant action you need get the full path for your action and that includes the namespace and the database name like the following:
/namespace/dbname/actionName
in my case it was /sansan/users/exec-query-find
so if you want to check whether the email exists or not in your cloudant db, and keep the original params just pass the following payload to your cloudant action
{
"data":{...},// some data you want to keep after the cloudant query
"query": {
"selector": {
"email": "email#domain.com"
}
},
"$actionName": "/sansan/users/exec-query-find",
"$forward": [// list of params you want forward
"data"
],
"$actionArgs": [ // list of params you want to feed the action
"query"
]
}
after running the sequence, the output should look like this:
{
"data": {...}, // your data
"docs": [...]// cloudant query results
}
the forward combinator is poorly documented, but you can find more details about it in Raymond Camden's blog post
look at Raymond's answer here too