optimize query

app/models/submission.rb

@@ -65,12 +65,18 @@ class Submission < ApplicationRecord
 
   scope :active, -> { where(archived_at: nil) }
   scope :archived, -> { where.not(archived_at: nil) }
-  scope :pending, -> { joins(:submitters).where(submitters: { completed_at: nil }).group(:id) }
+  scope :pending, lambda {
+    where(Submitter.where(Submitter.arel_table[:submission_id].eq(Submission.arel_table[:id])
+     .and(Submitter.arel_table[:completed_at].eq(nil))).select(1).arel.exists)
+  }
   scope :completed, lambda {
     where.not(Submitter.where(Submitter.arel_table[:submission_id].eq(Submission.arel_table[:id])
      .and(Submitter.arel_table[:completed_at].eq(nil))).select(1).arel.exists)
   }
-  scope :declined, -> { joins(:submitters).where.not(submitters: { declined_at: nil }).group(:id) }
+  scope :declined, lambda {
+    where(Submitter.where(Submitter.arel_table[:submission_id].eq(Submission.arel_table[:id])
+     .and(Submitter.arel_table[:declined_at].not_eq(nil))).select(1).arel.exists)
+  }
   scope :expired, -> { pending.where(expire_at: ..Time.current) }
 
   enum :source, {