add unique index to group id

Author: ramsayleung

app/models/group_classifier_state.rb

@@ -13,4 +13,6 @@ class GroupClassifierState < ApplicationRecord
   # find all classifiers for public, including group and username
   scope :for_public, -> { where(arel_table[:group_id].lteq(0)) }
   scope :for_group, -> { where("group_id < 0") }
+
+  validates :group_id, uniqueness: true
 end

db/migrate/20250920191408_add_unique_index_to_group_classifier_states_group_id.rb

@@ -0,0 +1,9 @@
+class AddUniqueIndexToGroupClassifierStatesGroupId < ActiveRecord::Migration[8.0]
+  def change
+    # Remove the old, non-unique index first.
+    remove_index :group_classifier_states, name: "index_group_classifier_states_on_group_id"
+
+    # Now, add the new index with a uniqueness constraint.
+    add_index :group_classifier_states, :group_id, unique: true
+  end
+end