Enforce uniqueness constraint on user_proxy_exercise_exercises

Similar to e9ab9f8, the table user_proxy_exercise_exercises lacked uniqueness constraints and a foreign key constraint. The model, in turn, has proper validations already in place.

The SQL query used in the migration aims to automatically delete duplicate entries. To do so, it builds a list of non-unique entries, sorts them according to their dense_rank() and (per User and ProxyExercise) removes all but the first.

Author: MrSerth

app/models/proxy_exercise.rb

@@ -69,10 +69,12 @@ def get_matching_exercise(user)
             raise "Unknown algorithm #{algorithm}"
         end
 
-      user.user_proxy_exercise_exercises << UserProxyExerciseExercise.create(user:,
+      user.user_proxy_exercise_exercises << UserProxyExerciseExercise.create!(user:,
         exercise: matching_exercise, proxy_exercise: self, reason: @reason.to_json)
       matching_exercise
     end
+  rescue ActiveRecord::RecordNotUnique, ActiveRecord::RecordInvalid
+    retry
   end
 
   def find_matching_exercise(user)

db/migrate/20250502170658_add_uniqueness_constraint_to_user_proxy_exercise_exercises.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+class AddUniquenessConstraintToUserProxyExerciseExercises < ActiveRecord::Migration[8.0]
+  class UserProxyExerciseExercise < ApplicationRecord
+  end
+
+  def change
+    change_column_null :user_proxy_exercise_exercises, :user_id, false
+    change_column_null :user_proxy_exercise_exercises, :user_type, false
+    change_column_null :user_proxy_exercise_exercises, :proxy_exercise_id, false
+    change_column_null :user_proxy_exercise_exercises, :exercise_id, false
+
+    add_foreign_key :user_proxy_exercise_exercises, :proxy_exercises
+    add_foreign_key :user_proxy_exercise_exercises, :exercises
+
+    up_only do
+      # We cannot add a unique index to a table that has duplicate rows.
+      # Hence, we keep the oldest row(s) and remove the others.
+      execute <<~SQL.squish
+        WITH duplicates AS (SELECT
+            dense_rank() over (PARTITION BY a.user_id, a.user_type, a.proxy_exercise_id, a.exercise_id ORDER BY a.created_at) AS row,
+            a.id AS upee_id
+          FROM user_proxy_exercise_exercises a
+          JOIN user_proxy_exercise_exercises b
+            ON a.user_id = b.user_id
+           AND a.user_type = b.user_type
+           AND a.proxy_exercise_id = b.proxy_exercise_id
+           AND a.exercise_id = b.exercise_id
+           AND a.id != b.id
+          ORDER BY a.created_at)
+        DELETE FROM user_proxy_exercise_exercises
+        WHERE id IN (SELECT upee_id FROM duplicates WHERE row != 1)
+      SQL
+    end
+
+    add_index :user_proxy_exercise_exercises, %i[user_id user_type proxy_exercise_id], unique: true
+  end
+end