WIP: use association manipulation iff external associations

For #121

lib/view_model/active_record/association_manipulation.rb

@@ -52,6 +52,10 @@ def load_associated(association_name, scope: nil, eager_include: true, serialize
   def replace_associated(association_name, update_hash, references: {}, deserialize_context: self.class.new_deserialize_context)
     association_data = self.class._association_data(association_name)
 
+    unless association_data.external?
+      raise ViewModel::DeserializationError::InternalAssociationWrite.new(association_name, self.to_reference)
+    end
+
     if association_data.referenced?
       is_fupdate =
         association_data.collection? &&
@@ -105,6 +109,10 @@ def append_associated(association_name, subtree_hash_or_hashes, references: {},
     direct_reflection = association_data.direct_reflection
     raise ArgumentError.new("Cannot append to single association '#{association_name}'") unless association_data.collection?
 
+    unless association_data.external?
+      raise ViewModel::DeserializationError::InternalAssociationWrite.new(association_name, self.to_reference)
+    end
+
     ViewModel::Utils.wrap_one_or_many(subtree_hash_or_hashes) do |subtree_hashes|
       model_class.transaction do
         ViewModel::Callbacks.wrap_deserialize(self, deserialize_context: deserialize_context) do |hook_control|
@@ -218,6 +226,10 @@ def delete_associated(association_name, associated_id, type: nil, deserialize_co
     association_data = self.class._association_data(association_name)
     direct_reflection = association_data.direct_reflection
 
+    unless association_data.external?
+      raise ViewModel::DeserializationError::InternalAssociationWrite.new(association_name, self.to_reference)
+    end
+
     unless association_data.collection?
       raise ArgumentError.new("Cannot remove element from single association '#{association_name}'")
     end

lib/view_model/active_record/update_data.rb

@@ -680,6 +680,12 @@ def parse(hash_data, valid_reference_keys)
         when AssociationData
           association_data = member_data
 
+          # FIXME: replace_associated uses this update machinery, this won't work
+          # until we mark it.
+          if association_data.external?
+            raise ViewModel::DeserializationError::ExternalAssociationWrite.new(name)
+          end
+
           case
           when value.nil?
             if association_data.collection?

lib/view_model/deserialization_error.rb

@@ -161,6 +161,33 @@ def meta
       end
     end
 
+    # Attempted to write to an external association during a deserialization
+    class ExternalAssociationWrite < InvalidRequest
+      attr_reader :association
+
+      def initialize(association, node)
+        @association = association
+        super([node])
+      end
+
+      def detail
+        "Invalid write to external association #{association} in deserialization"
+      end
+    end
+
+    # Attempted to write to an internal association during an association_manipulation
+    class InternalAssociationWrite < InvalidRequest
+      attr_reader :association
+      def initialize(association, node)
+        @association = association
+        super([node])
+      end
+
+      def detail
+        "Invalid write to internal association #{association} via external manipulation"
+      end
+    end
+
     class InvalidViewType < InvalidRequest
       attr_reader :expected_type
 

test/unit/view_model/active_record/has_many_test.rb

@@ -1087,6 +1087,10 @@ def new_model
     end
 
     describe 'with association manipulation' do
+      def subject_association_features
+        super.merge(external: true)
+      end
+
       it 'appends a child' do
         view = create_viewmodel!