anchor.diff:  %%--------------------------------------------------------------------
   -spec exists(model_behaviour:model_config(), datastore:ext_key()) ->
       {ok, boolean()} | datastore:generic_error().
  -exists(#model_config{link_store_level = ?GLOBAL_ONLY_LEVEL} = ModelConfig, Key) ->
  +exists(#model_config{link_store_level = L} = ModelConfig, Key)
  +    when L =:= ?GLOBAL_ONLY_LEVEL; L =:= ?LOCAL_ONLY_LEVEL ->
       direct_call(exists, ModelConfig, Key, [Key]);
   exists(ModelConfig, Key) ->
       direct_call(exists, ModelConfig, Key, [Key], {ok, false}).
  
positive.code: %%--------------------------------------------------------------------
  -spec fetch_link(model_behaviour:model_config(), datastore:ext_key(), datastore:link_name()) ->
      {ok, datastore:link_target()} | datastore:link_error().
  fetch_link(#model_config{link_store_level = ?GLOBAL_ONLY_LEVEL} = ModelConfig, Key, LinkName) ->
      direct_link_call(fetch_link, ModelConfig, Key, [Key, LinkName]);
  fetch_link(ModelConfig, Key, LinkName) ->
      direct_link_call(fetch_link, ModelConfig, Key, [Key, LinkName], {error, link_not_found}).
  
negative.code: %%--------------------------------------------------------------------
  -spec get_link_doc(model_behaviour:model_config(), binary(), DocKey :: datastore:ext_key(),
      MainDocKey :: datastore:ext_key()) -> {ok, datastore:document()} | datastore:generic_error().
  get_link_doc(#model_config{link_store_level = L} = ModelConfig, BucketOverride, DocKey, MainDocKey)
      when L =:= ?GLOBAL_ONLY_LEVEL; L =:= ?LOCAL_ONLY_LEVEL ->
      direct_link_call(get_link_doc, ModelConfig, MainDocKey, [BucketOverride, DocKey]);
  get_link_doc(#model_config{name = ModelName} = ModelConfig, BucketOverride, DocKey, MainDocKey) ->
      direct_link_call(get_link_doc, ModelConfig, MainDocKey, [BucketOverride, DocKey], {error, {not_found, ModelName}}).
  