Add new model flags

diffsync/__init__.py

@@ -175,11 +175,29 @@ def set_status(self, status: DiffSyncStatus, message: Text = ""):
         self._status = status
         self._status_message = message
 
+    @classmethod
+    def create_base(cls, diffsync: "DiffSync", ids: Mapping, attrs: Mapping) -> Optional["DiffSyncModel"]:
+        """Instantiate this class, along with any platform-specific data creation.
+
+        This method is not meant to be subclassed, users should redefine create() instead.
+
+        Args:
+            diffsync: The master data store for other DiffSyncModel instances that we might need to reference
+            ids: Dictionary of unique-identifiers needed to create the new object
+            attrs: Dictionary of additional attributes to set on the new object
+
+        Returns:
+            DiffSyncModel: instance of this class.
+        """
+        model = cls(**ids, diffsync=diffsync, **attrs)
+        model.set_status(DiffSyncStatus.SUCCESS, "Created successfully")
+        return model
+
     @classmethod
     def create(cls, diffsync: "DiffSync", ids: Mapping, attrs: Mapping) -> Optional["DiffSyncModel"]:
         """Instantiate this class, along with any platform-specific data creation.
 
-        Subclasses must call `super().create()`; they may wish to then override the default status information
+        Subclasses must call `super().create()` or `self.create_base()`; they may wish to then override the default status information
         by calling `set_status()` to provide more context (such as details of any interactions with underlying systems).
 
         Args:
@@ -194,14 +212,30 @@ def create(cls, diffsync: "DiffSync", ids: Mapping, attrs: Mapping) -> Optional[
         Raises:
             ObjectNotCreated: if an error occurred.
         """
-        model = cls(**ids, diffsync=diffsync, **attrs)
-        model.set_status(DiffSyncStatus.SUCCESS, "Created successfully")
-        return model
+        return cls.create_base(diffsync=diffsync, ids=ids, attrs=attrs)
+
+    def update_base(self, attrs: Mapping) -> Optional["DiffSyncModel"]:
+        """Base Update method to update the attributes of this instance, along with any platform-specific data updates.
+
+        This method is not meant to be subclassed, users should redefine update() instead.
+
+        Args:
+            attrs: Dictionary of attributes to update on the object
+
+        Returns:
+            DiffSyncModel: this instance.
+        """
+        for attr, value in attrs.items():
+            # TODO: enforce that only attrs in self._attributes can be updated in this way?
+            setattr(self, attr, value)
+
+        self.set_status(DiffSyncStatus.SUCCESS, "Updated successfully")
+        return self
 
     def update(self, attrs: Mapping) -> Optional["DiffSyncModel"]:
         """Update the attributes of this instance, along with any platform-specific data updates.
 
-        Subclasses must call `super().update()`; they may wish to then override the default status information
+        Subclasses must call `super().update()` or `self.update_base()`; they may wish to then override the default status information
         by calling `set_status()` to provide more context (such as details of any interactions with underlying systems).
 
         Args:
@@ -214,17 +248,23 @@ def update(self, attrs: Mapping) -> Optional["DiffSyncModel"]:
         Raises:
             ObjectNotUpdated: if an error occurred.
         """
-        for attr, value in attrs.items():
-            # TODO: enforce that only attrs in self._attributes can be updated in this way?
-            setattr(self, attr, value)
+        return self.update_base(attrs=attrs)
 
-        self.set_status(DiffSyncStatus.SUCCESS, "Updated successfully")
+    def delete_base(self) -> Optional["DiffSyncModel"]:
+        """Base delete method Delete any platform-specific data corresponding to this instance.
+
+        This method is not meant to be subclassed, users should redefine delete() instead.
+
+        Returns:
+            DiffSyncModel: this instance.
+        """
+        self.set_status(DiffSyncStatus.SUCCESS, "Deleted successfully")
         return self
 
     def delete(self) -> Optional["DiffSyncModel"]:
         """Delete any platform-specific data corresponding to this instance.
 
-        Subclasses must call `super().delete()`; they may wish to then override the default status information
+        Subclasses must call `super().delete()` or `self.delete_base()`; they may wish to then override the default status information
         by calling `set_status()` to provide more context (such as details of any interactions with underlying systems).
 
         Returns:
@@ -234,8 +274,7 @@ def delete(self) -> Optional["DiffSyncModel"]:
         Raises:
             ObjectNotDeleted: if an error occurred.
         """
-        self.set_status(DiffSyncStatus.SUCCESS, "Deleted successfully")
-        return self
+        return self.delete_base()
 
     @classmethod
     def get_type(cls) -> Text:

diffsync/enum.py

@@ -35,6 +35,20 @@ class DiffSyncModelFlags(enum.Flag):
     Can be used for the case where deletion of a model results in the automatic deletion of all its children.
     """
 
+    SKIP_UNMATCHED_SRC = 0b100
+    """Ignore the model if it only exists in the source/"from" DiffSync when determining diffs and syncing.
+
+    If this flag is set, no new model will be created in the target/"to" DiffSync.
+    """
+
+    SKIP_UNMATCHED_DST = 0b1000
+    """Ignore the model if it only exists in the target/"to" DiffSync when determining diffs and syncing.
+
+    If this flag is set, the model will not be deleted from the target/"to" DiffSync.
+    """
+
+    SKIP_UNMATCHED_BOTH = SKIP_UNMATCHED_SRC | SKIP_UNMATCHED_DST
+
 
 class DiffSyncFlags(enum.Flag):
     """Flags that can be passed to a sync_* or diff_* call to affect its behavior."""

diffsync/helpers.py

@@ -155,7 +155,7 @@ def validate_objects_for_diff(object_pairs: Iterable[Tuple[Optional["DiffSyncMod
                 if src_obj.get_identifiers() != dst_obj.get_identifiers():
                     raise ValueError(f"Keys mismatch: {src_obj.get_identifiers()} vs {dst_obj.get_identifiers()}")
 
-    def diff_object_pair(
+    def diff_object_pair(  # pylint: disable=too-many-return-statements
         self, src_obj: Optional["DiffSyncModel"], dst_obj: Optional["DiffSyncModel"]
     ) -> Optional[DiffElement]:
         """Diff the two provided DiffSyncModel objects and return a DiffElement or None.
@@ -180,11 +180,19 @@ def diff_object_pair(
 
         log = self.logger.bind(model=model, unique_id=unique_id)
         if self.flags & DiffSyncFlags.SKIP_UNMATCHED_SRC and not dst_obj:
-            log.debug("Skipping unmatched source object")
+            log.debug("Skipping due to SKIP_UNMATCHED_SRC flag on source adapter")
             self.incr_models_processed()
             return None
         if self.flags & DiffSyncFlags.SKIP_UNMATCHED_DST and not src_obj:
-            log.debug("Skipping unmatched dest object")
+            log.debug("Skipping due to SKIP_UNMATCHED_DST flag on source adapter")
+            self.incr_models_processed()
+            return None
+        if src_obj and not dst_obj and src_obj.model_flags & DiffSyncModelFlags.SKIP_UNMATCHED_SRC:
+            log.debug("Skipping due to SKIP_UNMATCHED_SRC flag on model")
+            self.incr_models_processed()
+            return None
+        if dst_obj and not src_obj and dst_obj.model_flags & DiffSyncModelFlags.SKIP_UNMATCHED_DST:
+            log.debug("Skipping due to SKIP_UNMATCHED_DST flag on model")
             self.incr_models_processed()
             return None
         if src_obj and src_obj.model_flags & DiffSyncModelFlags.IGNORE:
@@ -284,6 +292,7 @@ def __init__(  # pylint: disable=too-many-arguments
     ):
         """Create a DiffSyncSyncer instance, ready to call `perform_sync()` against."""
         self.diff = diff
+        self.src_diffsync = src_diffsync
         self.dst_diffsync = dst_diffsync
         self.flags = flags
         self.callback = callback
@@ -339,42 +348,51 @@ def sync_diff_element(self, element: DiffElement, parent_model: "DiffSyncModel"
         # We only actually need the "new" attrs to perform a create/update operation, and don't need any for a delete
         attrs = diffs.get("+", {})
 
-        model: Optional["DiffSyncModel"]
+        # Retrieve Source Object to get its flags
+        src_model: Optional["DiffSyncModel"]
         try:
-            model = self.dst_diffsync.get(self.model_class, ids)
-            model.set_status(DiffSyncStatus.UNKNOWN)
+            src_model = self.src_diffsync.get(self.model_class, ids)
         except ObjectNotFound:
-            model = None
+            src_model = None
 
-        changed, modified_model = self.sync_model(model, ids, attrs)
-        model = modified_model or model
+        # Retrieve Dest (and primary) Object
+        dst_model: Optional["DiffSyncModel"]
+        try:
+            dst_model = self.dst_diffsync.get(self.model_class, ids)
+            dst_model.set_status(DiffSyncStatus.UNKNOWN)
+        except ObjectNotFound:
+            dst_model = None
+
+        changed, modified_model = self.sync_model(src_model=src_model, dst_model=dst_model, ids=ids, attrs=attrs)
+        dst_model = modified_model or dst_model
 
-        if not modified_model or not model:
+        if not modified_model or not dst_model:
             self.logger.warning("No object resulted from sync, will not process child objects.")
             return changed
 
-        if self.action == DiffSyncActions.CREATE:
+        if self.action == DiffSyncActions.CREATE:  # type: ignore
             if parent_model:
-                parent_model.add_child(model)
-            self.dst_diffsync.add(model)
+                parent_model.add_child(dst_model)
+            self.dst_diffsync.add(dst_model)
         elif self.action == DiffSyncActions.DELETE:
             if parent_model:
-                parent_model.remove_child(model)
-            if model.model_flags & DiffSyncModelFlags.SKIP_CHILDREN_ON_DELETE:
-                # We don't need to process the child objects, but we do need to discard them from the dst_diffsync
-                self.dst_diffsync.remove(model, remove_children=True)
+                parent_model.remove_child(dst_model)
+
+            skip_children = bool(dst_model.model_flags & DiffSyncModelFlags.SKIP_CHILDREN_ON_DELETE)
+            self.dst_diffsync.remove(dst_model, remove_children=skip_children)
+
+            if skip_children:
                 return changed
-            self.dst_diffsync.remove(model)
 
         self.incr_elements_processed()
 
         for child in element.get_children():
-            changed |= self.sync_diff_element(child, parent_model=model)
+            changed |= self.sync_diff_element(child, parent_model=dst_model)
 
         return changed
 
-    def sync_model(
-        self, model: Optional["DiffSyncModel"], ids: Mapping, attrs: Mapping
+    def sync_model(  # pylint: disable=too-many-branches, unused-argument
+        self, src_model: Optional["DiffSyncModel"], dst_model: Optional["DiffSyncModel"], ids: Mapping, attrs: Mapping
     ) -> Tuple[bool, Optional["DiffSyncModel"]]:
         """Create/update/delete the current DiffSyncModel with current ids/attrs, and update self.status and self.message.
 
@@ -387,27 +405,27 @@ def sync_model(
             status = DiffSyncStatus.SUCCESS
             message = "No changes to apply; no action needed"
             self.log_sync_status(self.action, status, message)
-            return (False, model)
+            return (False, dst_model)
 
         try:
             self.logger.debug(f"Attempting model {self.action.value}")
             if self.action == DiffSyncActions.CREATE:
-                if model is not None:
+                if dst_model is not None:
                     raise ObjectNotCreated(f"Failed to create {self.model_class.get_type()} {ids} - it already exists!")
-                model = self.model_class.create(diffsync=self.dst_diffsync, ids=ids, attrs=attrs)
+                dst_model = self.model_class.create(diffsync=self.dst_diffsync, ids=ids, attrs=attrs)
             elif self.action == DiffSyncActions.UPDATE:
-                if model is None:
+                if dst_model is None:
                     raise ObjectNotUpdated(f"Failed to update {self.model_class.get_type()} {ids} - not found!")
-                model = model.update(attrs=attrs)
+                dst_model = dst_model.update(attrs=attrs)
             elif self.action == DiffSyncActions.DELETE:
-                if model is None:
+                if dst_model is None:
                     raise ObjectNotDeleted(f"Failed to delete {self.model_class.get_type()} {ids} - not found!")
-                model = model.delete()
+                dst_model = dst_model.delete()
             else:
                 raise ObjectCrudException(f'Unknown action "{self.action}"!')
 
-            if model is not None:
-                status, message = model.get_status()
+            if dst_model is not None:
+                status, message = dst_model.get_status()
             else:
                 status = DiffSyncStatus.FAILURE
                 message = f"{self.model_class.get_type()} {self.action.value} did not return the model object."
@@ -422,7 +440,7 @@ def sync_model(
 
         self.log_sync_status(self.action, status, message)
 
-        return (True, model)
+        return (True, dst_model)
 
     def log_sync_status(self, action: Optional[DiffSyncActions], status: DiffSyncStatus, message: str):
         """Log the current sync status at the appropriate verbosity with appropriate context.

docs/source/core_engine/01-flags.md

@@ -57,6 +57,9 @@ class MyAdapter(DiffSync):
 |---|---|---|
 | IGNORE | Do not render diffs containing this model; do not make any changes to this model when synchronizing.  Can be used to indicate a model instance that exists but should not be changed by DiffSync. | 0b1 |
 | SKIP_CHILDREN_ON_DELETE | When deleting this model, do not recursively delete its children. Can be used for the case where deletion of a model results in the automatic deletion of all its children. | 0b10 |
+| SKIP_UNMATCHED_SRC | Ignore the model if it only exists in the source/"from" DiffSync when determining diffs and syncing. If this flag is set, no new model will be created in the target/"to" DiffSync. | 0b100 |
+| SKIP_UNMATCHED_DST | Ignore the model if it only exists in the target/"to" DiffSync when determining diffs and syncing. If this flag is set, the model will not be deleted from the target/"to" DiffSync. | 0b1000 |
+| SKIP_UNMATCHED_BOTH | Convenience value combining both SKIP_UNMATCHED_SRC and SKIP_UNMATCHED_DST into a single flag | 0b1100 |
 
 ## Working with flags
 

tests/unit/conftest.py

@@ -65,6 +65,23 @@ def delete(self):
         return super().delete()  # type: ignore
 
 
+class ExceptionModelMixin:
+    """Test class that always throws exceptions when creating/updating/deleting instances."""
+
+    @classmethod
+    def create(cls, diffsync: DiffSync, ids: Mapping, attrs: Mapping):
+        """As DiffSyncModel.create(), but always throw exceptions."""
+        raise NotImplementedError
+
+    def update(self, attrs: Mapping):
+        """As DiffSyncModel.update(), but always throw exceptions."""
+        raise NotImplementedError
+
+    def delete(self):
+        """As DiffSyncModel.delete(), but always throw exceptions."""
+        raise NotImplementedError
+
+
 class Site(DiffSyncModel):
     """Concrete DiffSyncModel subclass representing a site or location that contains devices."""
 
@@ -300,6 +317,32 @@ def error_prone_backend_a():
     return diffsync
 
 
+class ExceptionSiteA(ExceptionModelMixin, SiteA):  # pylint: disable=abstract-method
+    """A Site that always throws exceptions."""
+
+
+class ExceptionDeviceA(ExceptionModelMixin, DeviceA):  # pylint: disable=abstract-method
+    """A Device that always throws exceptions."""
+
+
+class ExceptionInterface(ExceptionModelMixin, Interface):  # pylint: disable=abstract-method
+    """An Interface that always throws exceptions."""
+
+
+class ExceptionDeviceBackendA(BackendA):
+    """A variant of BackendA that always fails to create/update/delete Device objects."""
+
+    device = ExceptionDeviceA
+
+
+@pytest.fixture
+def exception_backend_a():
+    """Provide an instance of ExceptionBackendA subclass of DiffSync."""
+    diffsync = ExceptionDeviceBackendA()
+    diffsync.load()
+    return diffsync
+
+
 class SiteB(Site):
     """Extend Site with a `places` list."""