Constructing Materialized View or use ActiveRecord for polymorphic Rails models

Question

I'm working on an existing app which has the structure (simplified and) described below. One of our new queries is to find all activity in a company which is rather complicated and non-performant to build. It seems hard to write the query in ActiveRecord, so, I'm trying to use Scenic and build a Materialized View since this query is going to be mostly read-only.

So, we have Person, Group, Project, Report, Update and ActivityReceipt along with some join models. A person belongs to various groups and various projects.

My goal is to get show a feed of group activity of all of groups that a member is part of, so I'm looking to performantly fetch Activity by group, along with the author information, sorted by time and it seems like a materialized view with the following columns would make that happen:

activity_receipt_id, group_id, person_id

class Person < ApplicationRecord
  has_many :groups
  has_many :projects

end

class Membership < ApplicationRecord
  # id, group_id, person_id
  belongs_to :group
  belongs_to :person

end

class Company < ApplicationRecord
  has_many :projects
  has_many :people

end

class GroupDonation < ApplicationRecord
  # id, group_id, project_id
  belongs_to :group
  belongs_to :project_id

end

class Project < ApplicationRecord
  has_many :group_donations
  has_many :people
end

class ActivityReceipt < ApplicationRecord
  # polymorphic belongs_to relation to 'postable' which are reports, & updates
  # so, it has id, postable_id, and postable_type as columns and then other specific metadata
  belongs_to :postable
end

class Report < ApplicationRecord
  # project_id, membership_id and other specific metadata
  belongs_to :project
  belongs_to :membership #to track the author

  has_one :activity_receipt
end

class Update < ApplicationRecord
  # project_id, membership_id and other specific metadata
  belongs_to :project
  belongs_to :membership #to track the author

  has_one :activity_receipt
end

Conceptually, the query is for all the given group_ids, fetch the associated projects and then their associated reports & updates, and then their activity receipts which is eventually needed. I'm not very familiar with writing SQL to generate a view so I have been struggling on how to make such a materialized view with polymorphic relations, and if it is even possible / recommended

Here is what I have so far:

SELECT groups.id AS group_id, people.id AS people_id, activity_receipts.id as activity_receipt_id
FROM groups
JOIN group_donations ON group_donations.group_id = groups.id
JOIN projects ON projects.id = group_donations.group_id
JOIN reports ON reports.project_id = project.id
JOIN updates ON updates.project_id = project.id
JOIN activity_receipts ON 
// Stuck here