Support passing record to uniqueness conditions

activerecord/CHANGELOG.md

@@ -1,3 +1,16 @@
+*   Support passing record to uniqueness validator `:conditions` callable:
+
+    ```ruby
+    class Article < ApplicationRecord
+      validates_uniqueness_of :title, conditions: ->(article) {
+        published_at = article.published_at
+        where(published_at: published_at.beginning_of_year..published_at.end_of_year)
+      }
+    end
+    ```
+
+    *Eliot Sykes*
+
 *   `BatchEnumerator#update_all` and `BatchEnumerator#delete_all` now return the
     total number of rows affected, just like their non-batched counterparts.
 

activerecord/lib/active_record/validations/uniqueness.rb

@@ -29,7 +29,16 @@ def validate_each(record, attribute, value)
           end
         end
         relation = scope_relation(record, relation)
-        relation = relation.merge(options[:conditions]) if options[:conditions]
+
+        if options[:conditions]
+          conditions = options[:conditions]
+
+          relation = if conditions.arity.zero?
+            relation.instance_exec(&conditions)
+          else
+            relation.instance_exec(record, &conditions)
+          end
+        end
 
         if relation.exists?
           error_options = options.except(:case_sensitive, :scope, :conditions)
@@ -126,6 +135,17 @@ module ClassMethods
       #     validates_uniqueness_of :title, conditions: -> { where.not(status: 'archived') }
       #   end
       #
+      # To build conditions based on the record's state, define the conditions
+      # callable with a parameter, which will be the record itself. This
+      # example validates the title is unique for the year of publication:
+      #
+      #   class Article < ActiveRecord::Base
+      #     validates_uniqueness_of :title, conditions: ->(article) {
+      #       published_at = article.published_at
+      #       where(published_at: published_at.beginning_of_year..published_at.end_of_year)
+      #     }
+      #   end
+      #
       # When the record is created, a check is performed to make sure that no
       # record exists in the database with the given value for the specified
       # attribute (that maps to a column). When the record is updated,

activerecord/test/cases/validations/uniqueness_validation_test.rb

@@ -522,6 +522,23 @@ def test_validate_uniqueness_with_non_callable_conditions_is_not_supported
     }
   end
 
+  def test_validate_uniqueness_with_conditions_with_record_arg
+    Topic.validates_uniqueness_of :title, conditions: ->(record) {
+      where(written_on: record.written_on.beginning_of_day..record.written_on.end_of_day)
+    }
+
+    today_midday = Time.current.midday
+
+    todays_topic = Topic.new(title: "Highlights of the Day", written_on: today_midday)
+    assert todays_topic.save, "1st topic written today with this title should save"
+
+    todays_topic_duplicate = Topic.new(title: "Highlights of the Day", written_on: today_midday + 1.minute)
+    assert todays_topic_duplicate.invalid?, "2nd topic written today with this title should be invalid"
+
+    tomorrows_topic = Topic.new(title: "Highlights of the Day", written_on: today_midday + 1.day)
+    assert tomorrows_topic.valid?, "1st topic written tomorrow with this title should be valid"
+  end
+
   def test_validate_uniqueness_on_existing_relation
     event = Event.create
     assert_predicate TopicWithUniqEvent.create(event: event), :valid?