diff --git a/netx_api/models/port_traffic.py b/netx_api/models/port_traffic.py
index 4920371..9161a5b 100644
--- a/netx_api/models/port_traffic.py
+++ b/netx_api/models/port_traffic.py
@@ -3,13 +3,20 @@ from __future__ import annotations
 from datetime import datetime
 from uuid import uuid4
 
-from sqlalchemy import BigInteger, Boolean, DateTime, Float, ForeignKey, Integer, LargeBinary, String, Text, UniqueConstraint
+from sqlalchemy import BigInteger, Boolean, DateTime, Float, ForeignKey, Integer, LargeBinary, String, Text, UniqueConstraint, event
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from ..db import Base
 from ..timeutil import utcnow_naive
 from ._types import JsonType as _JsonType
 
+
+def _mirror_device_task_id(target: object) -> None:
+    """Keep legacy task_id column aligned with device_id (brownfield NOT NULL)."""
+    did = str(getattr(target, "device_id", None) or getattr(target, "task_id", None) or "")
+    target.device_id = did  # type: ignore[attr-defined]
+    target.task_id = did  # type: ignore[attr-defined]
+
 class PortTrafficDevice(Base):
     """Per-NE port traffic monitoring config (device-centric)."""
 
@@ -49,18 +56,12 @@ class PortTrafficSeries(Base):
 
     id: Mapped[str] = mapped_column(String(64), primary_key=True, default=lambda: uuid4().hex)
     device_id: Mapped[str] = mapped_column(String(64), default="", index=True)
+    # Legacy column retained for brownfield DBs that still enforce NOT NULL task_id.
+    task_id: Mapped[str] = mapped_column(String(64), default="")
     title: Mapped[str] = mapped_column(String(256), default="")
     status: Mapped[str] = mapped_column(String(32), default="active", index=True)  # active|disabled
     created_at: Mapped[datetime] = mapped_column(DateTime, default=utcnow_naive)
 
-    @property
-    def task_id(self) -> str:
-        return str(self.device_id or "")
-
-    @task_id.setter
-    def task_id(self, value: str) -> None:
-        self.device_id = str(value or "")
-
 
 class PortTrafficTarget(Base):
     """Monitored interface under a device monitoring config."""
@@ -69,6 +70,8 @@ class PortTrafficTarget(Base):
 
     id: Mapped[str] = mapped_column(String(64), primary_key=True, default=lambda: uuid4().hex)
     device_id: Mapped[str] = mapped_column(String(64), default="", index=True)
+    # Legacy column retained for brownfield DBs that still enforce NOT NULL task_id.
+    task_id: Mapped[str] = mapped_column(String(64), default="")
     series_id: Mapped[str] = mapped_column(String(64), default="", index=True)
     source: Mapped[str] = mapped_column(String(32), default="managed", index=True)
     target_id: Mapped[str] = mapped_column(String(128), index=True)  # NE id
@@ -83,13 +86,17 @@ class PortTrafficTarget(Base):
     last_sample_at: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)
     created_at: Mapped[datetime] = mapped_column(DateTime, default=utcnow_naive)
 
-    @property
-    def task_id(self) -> str:
-        return str(self.device_id or "")
 
-    @task_id.setter
-    def task_id(self, value: str) -> None:
-        self.device_id = str(value or "")
+@event.listens_for(PortTrafficSeries, "before_insert")
+@event.listens_for(PortTrafficSeries, "before_update")
+def _sync_series_task_id(mapper, connection, target) -> None:  # noqa: ANN001
+    _mirror_device_task_id(target)
+
+
+@event.listens_for(PortTrafficTarget, "before_insert")
+@event.listens_for(PortTrafficTarget, "before_update")
+def _sync_target_task_id(mapper, connection, target) -> None:  # noqa: ANN001
+    _mirror_device_task_id(target)
 
 
 class PortTrafficSample(Base):
diff --git a/netx_api/port_traffic_migrate.py b/netx_api/port_traffic_migrate.py
index c2fe92a..50df6d7 100644
--- a/netx_api/port_traffic_migrate.py
+++ b/netx_api/port_traffic_migrate.py
@@ -63,6 +63,27 @@ def ensure_port_traffic_series_schema(conn) -> None:
     conn.exec_driver_sql(
         "ALTER TABLE port_traffic_series ADD COLUMN IF NOT EXISTS task_id VARCHAR(64) DEFAULT ''"
     )
+    # Older installs created task_id as NOT NULL before the device-centric rename.
+    # Keep both columns populated and relax NOT NULL so ORM inserts that only set
+    # device_id (or only task_id) do not 500.
+    for sql in (
+        """
+        UPDATE port_traffic_series
+        SET device_id = task_id
+        WHERE COALESCE(device_id, '') = '' AND COALESCE(task_id, '') <> ''
+        """,
+        """
+        UPDATE port_traffic_series
+        SET task_id = device_id
+        WHERE COALESCE(task_id, '') = '' AND COALESCE(device_id, '') <> ''
+        """,
+        "ALTER TABLE port_traffic_series ALTER COLUMN task_id DROP NOT NULL",
+        "ALTER TABLE port_traffic_series ALTER COLUMN task_id SET DEFAULT ''",
+    ):
+        try:
+            conn.exec_driver_sql(sql)
+        except Exception:
+            pass
     conn.exec_driver_sql(
         "CREATE INDEX IF NOT EXISTS ix_port_traffic_series_device_id ON port_traffic_series (device_id)"
     )
@@ -79,6 +100,24 @@ def ensure_port_traffic_series_schema(conn) -> None:
     conn.exec_driver_sql(
         "ALTER TABLE port_traffic_target ADD COLUMN IF NOT EXISTS task_id VARCHAR(64) DEFAULT ''"
     )
+    for sql in (
+        """
+        UPDATE port_traffic_target
+        SET device_id = task_id
+        WHERE COALESCE(device_id, '') = '' AND COALESCE(task_id, '') <> ''
+        """,
+        """
+        UPDATE port_traffic_target
+        SET task_id = device_id
+        WHERE COALESCE(task_id, '') = '' AND COALESCE(device_id, '') <> ''
+        """,
+        "ALTER TABLE port_traffic_target ALTER COLUMN task_id DROP NOT NULL",
+        "ALTER TABLE port_traffic_target ALTER COLUMN task_id SET DEFAULT ''",
+    ):
+        try:
+            conn.exec_driver_sql(sql)
+        except Exception:
+            pass
     conn.exec_driver_sql(
         "CREATE INDEX IF NOT EXISTS ix_port_traffic_target_series_id ON port_traffic_target (series_id)"
     )