Add sub-component support via self-referential device hierarchy

models.py

@@ -32,6 +32,7 @@ class Device(Base):
     location      = Column(String(100), nullable=True)
     notes = Column(Text, nullable=True)
     ha_entity_id = Column(String(100), nullable=True)   # e.g. "sensor.tv_remote_battery"
+    parent_id = Column(Integer, ForeignKey("device.id", ondelete="SET NULL"), nullable=True)
 
     batteries = relationship("Battery", back_populates="device")
     logbook_entries = relationship(
@@ -40,6 +41,20 @@ class Device(Base):
         cascade="all, delete-orphan",
         single_parent=True,
     )
+    parent = relationship(
+        "Device",
+        back_populates="children",
+        primaryjoin="Device.parent_id == Device.id",
+        foreign_keys="[Device.parent_id]",
+        remote_side="[Device.id]",
+    )
+    children = relationship(
+        "Device",
+        back_populates="parent",
+        primaryjoin="Device.parent_id == Device.id",
+        foreign_keys="[Device.parent_id]",
+        order_by="Device.name",
+    )
 
     def installed_count(self):
         return sum(1 for b in self.batteries if b.status == "installed")
@@ -50,6 +65,12 @@ class Device(Base):
     def has_mixed_brands(self):
         return len(self.installed_brands()) > 1
 
+    def has_children(self):
+        return bool(self.children)
+
+    def is_subcomponent(self):
+        return self.parent_id is not None
+
     def __repr__(self):
         return f"<Device {self.name}>"