Fix error raised when handler doesn't exist

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -1006,7 +1006,16 @@ def flush_idle_connections!
       # for (not necessarily the current class).
       def retrieve_connection(spec_name) #:nodoc:
         pool = retrieve_connection_pool(spec_name)
-        raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found." unless pool
+
+        unless pool
+          # multiple database application
+          if ActiveRecord::Base.connection_handler != ActiveRecord::Base.default_connection_handler
+            raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found for the '#{ActiveRecord::Base.current_role}' role."
+          else
+            raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found."
+          end
+        end
+
         pool.connection
       end
 

activerecord/lib/active_record/connection_handling.rb

@@ -158,10 +158,6 @@ def lookup_connection_handler(handler_key) # :nodoc:
     end
 
     def with_handler(handler_key, &blk) # :nodoc:
-      unless ActiveRecord::Base.connection_handlers.keys.include?(handler_key)
-        raise ArgumentError, "The #{handler_key} role does not exist. Add it by establishing a connection with `connects_to` or use an existing role (#{ActiveRecord::Base.connection_handlers.keys.join(", ")})."
-      end
-
       handler = lookup_connection_handler(handler_key)
       swap_connection_handler(handler, &blk)
     end

activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb

@@ -336,13 +336,13 @@ def test_connection_handlers_swapping_connections_in_fiber
       end
 
       def test_calling_connected_to_on_a_non_existent_handler_raises
-        error = assert_raises ArgumentError do
+        error = assert_raises ActiveRecord::ConnectionNotEstablished do
           ActiveRecord::Base.connected_to(role: :reading) do
-            yield
+            Person.first
           end
         end
 
-        assert_equal "The reading role does not exist. Add it by establishing a connection with `connects_to` or use an existing role (writing).", error.message
+        assert_equal "No connection pool with 'primary' found for the 'reading' role.", error.message
       end
     end
   end

activerecord/test/cases/unconnected_test.rb

@@ -29,6 +29,14 @@ def test_connection_no_longer_established
     end
   end
 
+  def test_error_message_when_connection_not_established
+    error = assert_raise(ActiveRecord::ConnectionNotEstablished) do
+      TestRecord.find(1)
+    end
+
+    assert_equal "No connection pool with 'primary' found.", error.message
+  end
+
   def test_underlying_adapter_no_longer_active
     assert_not @underlying.active?, "Removed adapter should no longer be active"
   end