ENH: Add validation methods for all Entries

Entry.validate includes an apischema serialization roundtrip to enforce
type checks

Nestable validation includes cycle detection and making sure Nestables
aren't empty.

superscore/backends/test.py

@@ -7,7 +7,7 @@
 from superscore.backends.core import _Backend
 from superscore.errors import (BackendError, EntryExistsError,
                                EntryNotFoundError)
-from superscore.model import Collection, Entry, Snapshot
+from superscore.model import Entry, Nestable
 
 
 class TestBackend(_Backend):
@@ -28,7 +28,7 @@ def get_entry(self, uuid: UUID) -> Entry:
             entry = stack.pop()
             if entry.uuid == uuid:
                 return entry
-            if isinstance(entry, Collection) or isinstance(entry, Snapshot):
+            if isinstance(entry, Nestable):
                 stack.extend(entry.children)
         raise EntryNotFoundError(f"Entry {entry.uuid} could not be found")
 
@@ -45,4 +45,4 @@ def delete_entry(self, to_delete: Entry) -> None:
                     children.remove(entry)
                 elif entry.uuid == to_delete.uuid:
                     raise BackendError(f"Can't delete: entry {to_delete.uuid} is out of sync with the version in the backend")
-            stack.extend([entry.children for entry in children if isinstance(entry, Collection) or isinstance(entry, Snapshot)])
+            stack.extend([entry.children for entry in children if isinstance(entry, Nestable)])

superscore/model.py

@@ -1,6 +1,7 @@
 """Classes for representing data"""
 from __future__ import annotations
 
+import apischema
 import logging
 from dataclasses import dataclass, field
 from datetime import datetime
@@ -59,6 +60,20 @@ class Entry:
     description: str = ''
     creation_time: datetime = field(default_factory=utcnow)
 
+    def validate(self) -> bool:
+        """
+        Ensures Entry is properly formed.
+
+        Raises apischema.ValidationError if type checking fails during
+        deserialization
+        """
+        try:
+            serial = apischema.serialize(self)
+            apischema.deserialize(type(self), serial)
+            return True
+        except apischema.ValidationError:
+            return False
+
 
 @dataclass
 class Parameter(Entry):
@@ -69,6 +84,10 @@ class Parameter(Entry):
     readback: Optional[Parameter] = None
     read_only: bool = False
 
+    def validate(self) -> bool:
+        readback_is_valid = self.readback is None or self.readback.validate()
+        return readback_is_valid and super().validate()
+
 
 @dataclass
 class Value(Entry):
@@ -84,6 +103,10 @@ class Setpoint(Value):
     """A Value that can be written to the EPICS environment"""
     readback: Optional[Readback] = None
 
+    def validate(self) -> bool:
+        readback_is_valid = self.readback is None or self.readback.validate()
+        return readback_is_valid and super().validate()
+
 
 @dataclass
 class Readback(Value):
@@ -102,8 +125,39 @@ class Readback(Value):
     timeout: Optional[float] = None
 
 
+class Nestable:
+    """Abstract class that provides methods for nested container Entries"""
+    def validate(self):
+        """
+        Validates structure of Entry tree, then uses validate_nodes to validate
+        individual Entries. This separation avoids redundant work by only performing
+        tree-level validation once.  Overrides Entry.validate().
+        """
+        return not self.has_cycle() and super().validate() and self.validate_nodes()
+
+    def validate_nodes(self):
+        """
+        Validates self and all children at the Entry level. See Nestable.validate() for
+        more information.
+        """
+        not_empty = len(self.children) > 0
+        all_children_are_valid = all(child.validate_nodes() if isinstance(child, Nestable) else child.validate() for child in self.children)
+        return not_empty and all_children_are_valid
+
+    def has_cycle(self, parents=set()) -> bool:
+        if self.uuid in parents:
+            return True
+        else:
+            parents.add(self.uuid)
+            for child in self.children:
+                if isinstance(child, type(self)) and child.has_cycle(parents=parents):
+                    return True
+            parents.remove(self.uuid)
+            return False
+
+
 @dataclass
-class Collection(Entry):
+class Collection(Nestable, Entry):
     """Nestable group of Parameters and Collections"""
     meta_pvs: ClassVar[List[Parameter]] = []
     all_tags: ClassVar[Set[Tag]] = set()
@@ -114,7 +168,7 @@ class Collection(Entry):
 
 
 @dataclass
-class Snapshot(Entry):
+class Snapshot(Nestable, Entry):
     """
     Nestable group of Values and Snapshots.  Effectively a data-filled Collection
     """