diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,6 +3,7 @@
 # dependency lines, see https://pip.readthedocs.org/en/1.1/requirements.html
 
 arrow
+attrs
 celery >= 4
 # Not a direct dependency: missing from celery 4.4.4
 future >= 0.18.0
diff --git a/swh/scheduler/api/client.py b/swh/scheduler/api/client.py
--- a/swh/scheduler/api/client.py
+++ b/swh/scheduler/api/client.py
@@ -6,6 +6,7 @@
 
 from swh.core.api import RPCClient
 
+from .serializers import ENCODERS, DECODERS
 from ..interface import SchedulerInterface
 
 
@@ -15,3 +16,6 @@
     """
 
     backend_class = SchedulerInterface
+
+    extra_type_decoders = DECODERS
+    extra_type_encoders = ENCODERS
diff --git a/swh/scheduler/api/serializers.py b/swh/scheduler/api/serializers.py
new file mode 100644
--- /dev/null
+++ b/swh/scheduler/api/serializers.py
@@ -0,0 +1,28 @@
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+"""Decoder and encoders for swh.scheduler.model objects."""
+
+from typing import Callable, Dict, List, Tuple
+
+import attr
+
+import swh.scheduler.model as model
+
+
+def _encode_model_object(obj):
+    d = attr.asdict(obj)
+    d["__type__"] = type(obj).__name__
+    return d
+
+
+ENCODERS: List[Tuple[type, str, Callable]] = [
+    (model.BaseSchedulerModel, "scheduler_model", _encode_model_object),
+]
+
+
+DECODERS: Dict[str, Callable] = {
+    "scheduler_model": lambda d: getattr(model, d.pop("__type__"))(**d)
+}
diff --git a/swh/scheduler/api/server.py b/swh/scheduler/api/server.py
--- a/swh/scheduler/api/server.py
+++ b/swh/scheduler/api/server.py
@@ -13,6 +13,7 @@
 
 from swh.scheduler import get_scheduler
 from swh.scheduler.interface import SchedulerInterface
+from .serializers import ENCODERS, DECODERS
 
 
 scheduler = None
@@ -26,7 +27,8 @@
 
 
 class SchedulerServerApp(RPCServerApp):
-    pass
+    extra_type_decoders = DECODERS
+    extra_type_encoders = ENCODERS
 
 
 app = SchedulerServerApp(
diff --git a/swh/scheduler/model.py b/swh/scheduler/model.py
new file mode 100644
--- /dev/null
+++ b/swh/scheduler/model.py
@@ -0,0 +1,26 @@
+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from typing import List, Optional, Tuple
+
+import attr
+import attr.converters
+
+
+@attr.s
+class BaseSchedulerModel:
+    _columns: Optional[List[str]] = None
+
+    @classmethod
+    def columns(cls) -> List[str]:
+        if cls._columns is None:
+            columns: List[Tuple[str, int]] = []
+            for field in attr.fields(cls):
+                columns.append(
+                    (field.name, 0 if field.metadata.get("primary_key") else 1)
+                )
+            cls._columns = [c[0] for c in sorted(columns, key=lambda c: (c[1], c[0]))]
+
+        return cls._columns