feat(transports): pass get obj None checks to user

also adds copy obj and children method

speckle/transports/abstract_transport.py

@@ -63,8 +63,8 @@ class AbstractTransport(Transport):
         pass
 
     @abstractmethod
-    def get_object(self, id: str) -> str:
-        """Gets an object
+    def get_object(self, id: str) -> str or None:
+        """Gets an object. Returns `None` if the object is not found.
 
         Arguments:
             id {str} -- the hash of the object
@@ -73,3 +73,15 @@ class AbstractTransport(Transport):
             str -- the full string representation of the object (or null of no object is found)
         """
         pass
+
+    @abstractmethod
+    def copy_object_and_children(self, id: str, target_transport: Transport) -> str:
+        """Copies the parent object and all its children to the provided transport.
+
+        Arguments:
+            id {str} -- the id of the object you want to copy
+            target_transport {AbstractTransport} -- the transport you want to copy the object to
+        Returns:
+            str -- the string representation of the root object
+        """
+        pass

speckle/transports/memory.py

@@ -25,14 +25,19 @@ class MemoryTransport(AbstractTransport):
     ) -> None:
         raise NotImplementedError
 
-    def get_object(self, id: str) -> str:
+    def get_object(self, id: str) -> str or None:
         if id in self.objects:
             return self.objects[id]
         else:
-            raise SpeckleException("No object found in this memory transport")
+            return None
 
     def begin_write(self) -> None:
         self.saved_object_count = 0
 
     def end_write(self) -> None:
         pass
+
+    def copy_object_and_children(
+        self, id: str, target_transport: AbstractTransport
+    ) -> str:
+        raise NotImplementedError

speckle/transports/sqlite.py

@@ -105,13 +105,13 @@ class SQLiteTransport(AbstractTransport):
             print(e)
             raise e
 
-    def get_object(self, id: str) -> tuple:
+    def get_object(self, id: str) -> str or None:
         self.__check_connection()
         with closing(self.__connection.cursor()) as c:
             row = c.execute(
                 "SELECT * FROM objects WHERE hash = ? LIMIT 1", (id,)
             ).fetchone()
-        return row
+        return row[1] if row else None
 
     def begin_write(self):
         self.saved_obj_count = 0
@@ -119,6 +119,11 @@ class SQLiteTransport(AbstractTransport):
     def end_write(self):
         pass
 
+    def copy_object_and_children(
+        self, id: str, target_transport: AbstractTransport
+    ) -> str:
+        raise NotImplementedError
+
     def close(self):
         """Close the connection to the database"""
         if self.__connection: