AWS Amplify GraphQL CreateOrUpdate / Upsert mutation

Question

Minor newbie with GraphQL so I'm a little bit lost here. How would I go about creating a CreateOrUpdate mutation/resolver for a model on AWS Amplify?

I'm running a lambda function after every user auth to hit a third party API and pull back relevant data to that user. The entities that come back may already be stored but related to another user. I'm assuming there's a better way than attempting to Create, catching an error and then attempting to Fetch & Update with the new user appended to the users field?!

type Event
@model
@auth(rules: [
  {allow: public, provider: apiKey, operations: [read, create, update, delete]}
  {allow: owner, ownerField: "users"}
])
@key(fields: ["venue", "date"])
{
  id: ID!
  venue: String!
  date: AWSDate!
  ref: String!
  users: [String]!
}

Any help massively appreciated (even just good resources to read up on writing resolvers - looking at the generated Mutation.updateEvent.req.vtl file for inspiration is a bit intimidating)

Answer 1

You need to override the generated resolver for update mutation.

Just copy the content of the autogenerated resolvers and make some changes.

File name may look like this:

<project-root>/amplify/backend/api/<api-name>/build/resolvers/<TypeName>.<FieldName>.<req/res>.vlt

To override, copy this file to:

<project-root>/amplify/backend/api/<api-name>/resolvers/<TypeName>.<FieldName>.<req/res>.vlt

For example: amplify/backend/api/blog/build/resolvers/Mutation.updatePost.req.vtl

Then remove these line:

## Begin - key condition **
#if( $ctx.stash.metadata.modelObjectKey )
  #set( $keyConditionExpr = {} )
  #set( $keyConditionExprNames = {} )
  #foreach( $entry in $ctx.stash.metadata.modelObjectKey.entrySet() )
    $util.qr($keyConditionExpr.put("keyCondition$velocityCount", {
  "attributeExists": true
}))
    $util.qr($keyConditionExprNames.put("#keyCondition$velocityCount", "$entry.key"))
  #end
  $util.qr($ctx.stash.conditions.add($keyConditionExpr))
#else
  $util.qr($ctx.stash.conditions.add({
  "id": {
      "attributeExists": true
  }
}))
#end

That part of vtl code checks that the id on update mutation should exists.