Avoid loading all tasks to validate a Run#task_name

app/models/maintenance_tasks/run.rb

@@ -36,9 +36,7 @@ class Run < ApplicationRecord
 
     enum status: STATUSES.to_h { |status| [status, status.to_s] }
 
-    validates :task_name, on: :create, inclusion: {
-      in: ->(_) { Task.available_tasks.map(&:to_s) },
-    }
+    validate :task_name_belongs_to_a_valid_task, on: :create
     validate :csv_attachment_presence, on: :create
     validate :csv_content_type, on: :create
     validate :validate_task_arguments, on: :create
@@ -339,6 +337,15 @@ def stuck?
       cancelling? && updated_at <= STUCK_TASK_TIMEOUT.ago
     end
 
+    # Performs validation on the task_name attribute.
+    # A Run must be associated with a valid Task to be valid.
+    # In order to confirm that, the Task is looked up by name.
+    def task_name_belongs_to_a_valid_task
+      Task.named(task_name)
+    rescue Task::NotFoundError
+      errors.add(:task_name, "must be the name of an existing Task.")
+    end
+
     # Performs validation on the presence of a :csv_file attachment.
     # A Run for a Task that uses CsvCollection must have an attached :csv_file
     # to be valid. Conversely, a Run for a Task that doesn't use CsvCollection

test/models/maintenance_tasks/runner_test.rb

@@ -61,7 +61,7 @@ class RunnerTest < ActiveSupport::TestCase
           end
 
           assert_equal(
-            "Validation failed: Task name is not included in the list",
+            "Validation failed: Task name must be the name of an existing Task.",
             error.message,
           )
         end