How can I use the context during a subscription.trigger?

[dominikklein]

The subscription trigger has the following parameters:

#trigger(event_name, args, object, scope: nil, context: {}) ⇒ void

What is the use case of the context here? In my situation, I want to handover some additional context to the possible executed subscription?

[rmosolgo]

Hi! Good question. I'm honestly not sure what that'd come in handy for. Here's the source:

graphql-ruby/lib/graphql/subscriptions.rb

Lines 60 to 93 in a814873

	def trigger(event_name, args, object, scope: nil, context: {})
	# Make something as context-like as possible, even though there isn't a current query:
	dummy_query = @schema.query_class.new(@schema, "{ __typename }", validate: false, context: context)
	context = dummy_query.context
	event_name = event_name.to_s
	# Try with the verbatim input first:
	field = dummy_query.types.field(@schema.subscription, event_name) # rubocop:disable Development/ContextIsPassedCop
	if field.nil?
	# And if it wasn't found, normalize it:
	normalized_event_name = normalize_name(event_name)
	field = dummy_query.types.field(@schema.subscription, normalized_event_name) # rubocop:disable Development/ContextIsPassedCop
	if field.nil?
	raise InvalidTriggerError, "No subscription matching trigger: #{event_name} (looked for #{@schema.subscription.graphql_name}.#{normalized_event_name})"
	end
	else
	# Since we found a field, the original input was already normalized
	normalized_event_name = event_name
	end
	# Normalize symbol-keyed args to strings, try camelizing them
	# Should this accept a real context somehow?
	normalized_args = normalize_arguments(normalized_event_name, field, args, GraphQL::Query::NullContext.instance)
	event = Subscriptions::Event.new(
	name: normalized_event_name,
	arguments: normalized_args,
	field: field,
	scope: scope,
	context: context,
	)
	execute_all(event, object)
	end

It looks like there, it would be used for finding the field that the trigger refers to, so it would be passed to visible? methods.

It's also passed to Subscriptions::Event.new, so its used a few places there:

https://github.com/rmosolgo/graphql-ruby/blob/a814873ce391f9031bbb6465edf02c13d419e33f/lib/graphql/subscriptions/event.rb#L42C27-L42C41

graphql-ruby/lib/graphql/subscriptions/event.rb

Line 36 in a814873

@topic = self.class.serialize(name, arguments, field, scope: scope_val, context: context)

And I think this is a red herring, it's used when running the initial subscription, but not used for subsequent updates:

graphql-ruby/lib/graphql/subscriptions/event.rb

Lines 46 to 60 in a814873

	# @return [String] a logical identifier for this event. (Stable when the query is broadcastable.)
	def fingerprint
	@fingerprint ||= begin
	# When this query has been flagged as broadcastable,
	# use a generalized, stable fingerprint so that
	# duplicate subscriptions can be evaluated and distributed in bulk.
	# (`@topic` includes field, args, and subscription scope already.)
	if @context.namespace(:subscriptions)[:subscription_broadcastable]
	"#{@topic}/#{@context.query.fingerprint}"
	else
	# not broadcastable, build a unique ID for this event
	@context.schema.subscriptions.build_id
	end
	end
	end

Is there something particular you're hoping to use it for? Or something you tried but didn't work?

[dominikklein]

Our use case is that we have a subscription that should not be triggered when the "own" browser tab is using the mutation. We tried to have a unique id for the browser tab. But failed to have a handover of this id during the triggering.