Add 'deleted' column to SchoolClasses record and DB

This commit adds the 'deleted' column on the SchoolClass record and DB
migration, as well as two scopes called `active` and `deleted` to
simplify retrieval of active and deleted classes respectively.

Author: fspeirs

app/models/school_class.rb

@@ -8,6 +8,8 @@ class SchoolClass < ApplicationRecord
   accepts_nested_attributes_for :teachers
 
   scope :with_teachers, ->(user_id) { joins(:teachers).where(teachers: { id: user_id }) }
+  scope :active, -> { where(deleted: false) }
+  scope :deleted, -> { where(deleted: true) }
 
   before_validation :assign_class_code, on: %i[create import]
 
@@ -73,6 +75,17 @@ def submitted_count
       .count
   end
 
+  def deleted?
+    deleted
+  end
+
+  def mark_as_deleted!
+    return if deleted?
+
+    self.deleted = true
+    save!(validate: false)
+  end
+
   private
 
   def school_class_has_at_least_one_teacher

db/migrate/20260113131231_add_deleted_to_school_classes.rb

@@ -0,0 +1,6 @@
+class AddDeletedToSchoolClasses < ActiveRecord::Migration[7.2]
+  def change
+    add_column :school_classes, :deleted, :boolean, default: false, null: false
+    add_index :school_classes, :deleted
+  end
+end