Fix races that lead to duplicate votes creation

CHANGELOG.md

@@ -0,0 +1,37 @@
+# Change log
+
+## master (unreleased)
+
+### Bug Fixes
+
+* [#127](https://github.com/ryanto/acts_as_votable/issues/127): Fix races that lead to duplicate votes creation. ([@fatkodima][])
+
+  For this to work, you need to update your database schema and existing data.
+  ```ruby
+  # 1. Add a new column to the `votes` table.
+  add_column :votes, :uniqueness_token, :string
+
+  # 2. Manually remove erroneously created duplicate votes.
+
+  # 3. If you are using `duplicate: true` while voting in your codebase,
+  # update all those duplicated votes by setting a unique `uniqueness_token` for each of them,
+  # something like a unique hex value would suffice.
+
+  # 4. For other non duplicated votes update all of them setting the
+  # `uniqueness_token` field to "unique vote" string value.
+
+  # 5. Update `uniqueness_token` column to disallow NULL values.
+  change_column_null :votes, :uniqueness_token, false
+
+  # 6. Add a new unique index
+  add_index :votes, [:voter_id, :voter_type, :vote_scope, :votable_id, :votable_type, :uniqueness_token],
+    name: "index_votes_uniqueness", unique: true
+
+  # 7. Now you can delete the old index
+  remove_index :votes, [:voter_id, :voter_type, :vote_scope]
+  ```
+
+  NOTE: Make sure you adapted that steps for your workload and run that commands safely
+  (adding/removing indexes concurrently, updating columns in batches, etc).
+
+[@fatkodima]: https://github.com/fatkodima

lib/acts_as_votable/votable.rb

@@ -63,6 +63,9 @@ def default_conditions
       }
     end
 
+    UNIQUE_VOTE_TOKEN = "unique vote"
+    private_constant :UNIQUE_VOTE_TOKEN
+
     # voting
     def vote_by(args = {})
       return false if args[:voter].nil?
@@ -81,6 +84,13 @@ def vote_by(args = {})
           voter: options[:voter],
           vote_scope: options[:vote_scope]
         )
+
+        if options[:duplicate]
+          require "securerandom"
+          vote.uniqueness_token = SecureRandom.hex
+        else
+          vote.uniqueness_token = UNIQUE_VOTE_TOKEN
+        end
       else
         # this voter is potentially changing his vote
         vote = votes.last

lib/acts_as_votable/vote.rb

@@ -21,7 +21,8 @@ class Vote < ::ActiveRecord::Base
     scope :for_type, ->(klass) { where(votable_type: klass.to_s) }
     scope :by_type, ->(klass) { where(voter_type: klass.to_s) }
 
-    validates_presence_of :votable_id
-    validates_presence_of :voter_id
+    validates :votable_id, presence: true
+    validates :voter_id, presence: true,
+      uniqueness: { scope: [:voter_type, :vote_scope, :votable, :uniqueness_token] }
   end
 end

lib/generators/acts_as_votable/migration/templates/active_record/migration.erb

@@ -1,22 +1,20 @@
 class ActsAsVotableMigration < ActiveRecord::Migration<%= migration_version %>
-  def self.up
+  def change
     create_table :votes do |t|
+      t.references :votable, null: false, polymorphic: true, index: false
+      t.references :voter, null: false, polymorphic: true, index: false
 
-      t.references :votable, :polymorphic => true
-      t.references :voter, :polymorphic => true
-
-      t.boolean :vote_flag
+      t.boolean :vote_flag, null: false, default: true
       t.string :vote_scope
-      t.integer :vote_weight
+      t.integer :vote_weight, null: false, default: 1
+      t.string :uniqueness_token, null: false # used for 'duplicate' feature
 
       t.timestamps
-    end
 
-    add_index :votes, [:voter_id, :voter_type, :vote_scope]
-    add_index :votes, [:votable_id, :votable_type, :vote_scope]
-  end
+      t.index [:voter_id, :voter_type, :vote_scope, :votable_id, :votable_type, :uniqueness_token],
+        name: "index_votes_uniqueness", unique: true
 
-  def self.down
-    drop_table :votes
+      t.index [:votable_id, :votable_type, :vote_scope]
+    end
   end
 end

spec/spec_helper.rb

@@ -18,17 +18,18 @@
     t.references :votable, polymorphic: true
     t.references :voter, polymorphic: true
 
-    t.boolean :vote_flag
+    t.boolean :vote_flag, null: false, default: true
     t.string :vote_scope
-    t.integer :vote_weight
+    t.integer :vote_weight, null: false, default: 1
+    t.string :uniqueness_token, null: false
 
     t.timestamps
-  end
 
-  add_index :votes, [:votable_id, :votable_type]
-  add_index :votes, [:voter_id, :voter_type]
-  add_index :votes, [:voter_id, :voter_type, :vote_scope]
-  add_index :votes, [:votable_id, :votable_type, :vote_scope]
+    t.index [:voter_id, :voter_type, :vote_scope, :votable_id, :votable_type, :uniqueness_token],
+      name: "index_votes_uniqueness", unique: true
+
+    t.index [:votable_id, :votable_type, :vote_scope]
+  end
 
   create_table :voters do |t|
     t.string :name