1 files changed, 43 insertions, 5 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 37506a97e2..a518b897a0 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -53,8 +53,6 @@ module ActiveRecord
 
       def initialize(connection, logger, connection_options, config)
         super(connection, logger, config)
-
-        @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
       end
 
       def version #:nodoc:
@@ -109,6 +107,14 @@ module ActiveRecord
         true
       end
 
+      def supports_insert_on_duplicate_skip?
+        true
+      end
+
+      def supports_insert_on_duplicate_update?
+        true
+      end
+
       def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
         query_value("SELECT GET_LOCK(#{quote(lock_name.to_s)}, #{timeout})") == 1
       end
@@ -154,10 +160,9 @@ module ActiveRecord
 
       # CONNECTION MANAGEMENT ====================================
 
-      # Clears the prepared statements cache.
-      def clear_cache!
+      def clear_cache! # :nodoc:
         reload_type_map
-        @statements.clear
+        super
       end
 
       #--
@@ -453,6 +458,21 @@ module ActiveRecord
         SQL
       end
 
+      def default_uniqueness_comparison(attribute, value, klass) # :nodoc:
+        column = column_for_attribute(attribute)
+
+        if column.collation && !column.case_sensitive? && !value.nil?
+          ActiveSupport::Deprecation.warn(<<~MSG.squish)
+            Uniqueness validator will no longer enforce case sensitive comparison in Rails 6.1.
+            To continue case sensitive comparison on the :#{attribute.name} attribute in #{klass} model,
+            pass `case_sensitive: true` option explicitly to the uniqueness validator.
+          MSG
+          attribute.eq(Arel::Nodes::Bin.new(value))
+        else
+          super
+        end
+      end
+
       def case_sensitive_comparison(attribute, value) # :nodoc:
         column = column_for_attribute(attribute)
 
@@ -497,6 +517,20 @@ module ActiveRecord
         end
       end
 
+      def build_insert_sql(insert) # :nodoc:
+        sql = +"INSERT #{insert.into} #{insert.values_list}"
+
+        if insert.skip_duplicates?
+          any_column = quote_column_name(insert.model.columns.first.name)
+          sql << " ON DUPLICATE KEY UPDATE #{any_column}=#{any_column}"
+        elsif insert.update_duplicates?
+          sql << " ON DUPLICATE KEY UPDATE "
+          sql << insert.updatable_columns.map { |column| "#{column}=VALUES(#{column})" }.join(",")
+        end
+
+        sql
+      end
+
       private
         def check_version
           if version < "5.5.8"
@@ -770,6 +804,10 @@ module ActiveRecord
           Arel::Visitors::MySQL.new(self)
         end
 
+        def build_statement_pool
+          StatementPool.new(self.class.type_cast_config_to_integer(@config[:statement_limit]))
+        end
+
         def mismatched_foreign_key(message, sql:, binds:)
           match = %r/
             (?:CREATE|ALTER)\s+TABLE\s*(?:`?\w+`?\.)?`?(?<table>\w+)`?.+?