Get all tests passing on MySQL and PostgreSQL on Rails 6.0.0

.ruby-version

@@ -1 +1 @@
-2.2.2
+2.5.2

Gemfile

@@ -1,6 +1,8 @@
 source 'https://rubygems.org'
 
-gem 'activerecord', '~> 6.0.0.rc1'
+
+gem 'activerecord', '~> 6.0.0'
+
 gem 'rake'
 gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw]
 

composite_primary_keys.gemspec

@@ -27,7 +27,7 @@ Gem::Specification.new do |s|
   # Dependencies
   s.required_ruby_version = '>= 2.2.2'
 
-  s.add_dependency('activerecord', '~> 6.0.0.rc1')
+  s.add_dependency('activerecord', '~> 6.0.0')
 
   s.add_development_dependency('rake')
   s.add_development_dependency('mysql2')

lib/composite_primary_keys.rb

@@ -26,7 +26,7 @@
 
 unless defined?(ActiveRecord)
   require 'rubygems'
-  gem 'activerecord', '6.0.0.rc1'
+  gem 'activerecord', '6.0.0'
   require 'active_record'
 end
 

lib/composite_primary_keys/relation.rb

@@ -28,11 +28,13 @@ def update_all(updates)
       # CPK
       if @klass.composite?
         stmt.table(table)
-        subselect = arel.clone
+
         arel_attributes = primary_keys.map do |key|
           arel_attribute(key)
         end.to_composite_keys
-        subselect.projections = arel_attributes
+
+        subselect = subquery_for(arel_attributes, arel)
+
         stmt.wheres = [arel_attributes.in(subselect)]
       else
         stmt.table(arel.join_sources.empty? ? table : arel.source)
@@ -76,11 +78,13 @@ def delete_all
       # CPK
       if @klass.composite?
         stmt.from(table)
-        subselect = arel.clone
+
         arel_attributes = primary_keys.map do |key|
           arel_attribute(key)
         end.to_composite_keys
-        subselect.projections = arel_attributes
+
+        subselect = subquery_for(arel_attributes, arel)
+
         stmt.wheres = [arel_attributes.in(subselect)]
       else
         stmt.from(arel.join_sources.empty? ? table : arel.source)
@@ -96,5 +100,19 @@ def delete_all
       reset
       affected
     end
+
+    # CPK
+    def subquery_for(key, select)
+      subselect = select.clone
+      subselect.projections = key
+
+      # Materialize subquery by adding distinct
+      # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
+      subselect.distinct unless select.limit || select.offset || select.orders.any?
+
+      key_name = Array(key).map {|a_key| a_key.name }.join(',')
+
+      Arel::SelectManager.new(subselect.as("__active_record_temp")).project(Arel.sql(key_name))
+    end
   end
 end

lib/composite_primary_keys/relation/calculations.rb

@@ -57,6 +57,11 @@ def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
       def build_count_subquery(relation, column_name, distinct)
         if column_name == :all
           relation.select_values = [ Arel.sql(::ActiveRecord::FinderMethods::ONE_AS_ONE) ] unless distinct
+          if relation.select_values.first.is_a?(Array)
+            relation.select_values = relation.select_values.first.map do |column|
+              Arel::Attribute.new(@klass.unscoped.table, column)
+            end
+          end
         elsif column_name.is_a?(Array)
           relation.select_values = column_name.map do |column|
             Arel::Attribute.new(@klass.unscoped.table, column)

lib/composite_primary_keys/relation/finder_methods.rb

@@ -2,7 +2,7 @@ module CompositePrimaryKeys
   module ActiveRecord
     module FinderMethods
       def apply_join_dependency(eager_loading: group_values.empty?)
-        join_dependency = construct_join_dependency(eager_load_values + includes_values)
+        join_dependency = construct_join_dependency(eager_load_values + includes_values, Arel::Nodes::OuterJoin)
         relation = except(:includes, :eager_load, :preload).joins!(join_dependency)
 
         if eager_loading && !using_limitable_reflections?(join_dependency.reflections)
@@ -51,7 +51,7 @@ def construct_relation_for_exists(conditions)
         conditions = sanitize_forbidden_attributes(conditions)
 
         if distinct_value && offset_value
-          relation = limit(1)
+          relation = except(:order).limit!(1)
         else
           relation = except(:select, :distinct, :order)._select!(::ActiveRecord::FinderMethods::ONE_AS_ONE).limit!(1)
         end