diff --git a/etebase_fastapi/collection.py b/etebase_fastapi/collection.py
index f687127..5656fb6 100644
--- a/etebase_fastapi/collection.py
+++ b/etebase_fastapi/collection.py
@@ -14,7 +14,7 @@ from pydantic import BaseModel
 from django_etebase import models
 from django_etebase.models import Collection, AccessLevels, CollectionMember
 from .authentication import get_authenticated_user
-from .exceptions import ValidationError
+from .exceptions import ValidationError, transform_validation_error
 from .msgpack import MsgpackRoute, MsgpackResponse
 from .stoken_handler import filter_by_stoken_and_limit
 
@@ -79,7 +79,7 @@ class CollectionItemOut(CollectionItemCommon):
             version=obj.version,
             encryptionKey=obj.encryptionKey,
             etag=obj.etag,
-            content=CollectionItemRevisionOut.from_orm_context(obj.content, context),
+            content=CollectionItemRevision.from_orm_context(obj.content, context),
         )
 
 
@@ -125,11 +125,26 @@ class ItemDepIn(BaseModel):
     etag: str
     uid: str
 
+    def validate_db(self):
+        item = models.CollectionItem.objects.get(uid=self.uid)
+        etag = self.etag
+        if item.etag != etag:
+            raise ValidationError(
+                "wrong_etag",
+                "Wrong etag. Expected {} got {}".format(item.etag, etag),
+                status_code=status.HTTP_409_CONFLICT,
+            )
+
 
 class ItemBatchIn(BaseModel):
     items: t.List[CollectionItemIn]
     deps: t.Optional[ItemDepIn]
 
+    def validate_db(self):
+        if self.deps is not None:
+            for key, _value in self.deps:
+                getattr(self.deps, key).validate_db()
+
 
 @sync_to_async
 def list_common(
@@ -172,7 +187,7 @@ async def collection_list(
     pass
 
 
-def process_revisions_for_item(item: models.CollectionItem, revision_data: CollectionItemRevisionOut):
+def process_revisions_for_item(item: models.CollectionItem, revision_data: CollectionItemRevision):
     chunks_objs = []
 
     revision = models.CollectionItemRevision(**revision_data.dict(exclude={"chunks"}), item=item)
@@ -250,16 +265,60 @@ def get_collection(uid: str, user: User = Depends(get_authenticated_user), prefe
     return MsgpackResponse(ret)
 
 
-def item_bulk_common(data: ItemBatchIn, user: User, stoken: str, uid: str, validate_etag: bool):
+def item_create(item_model: CollectionItemIn, validate_etag: bool):
+    """Function that's called when this serializer creates an item"""
+    etag = item_model.etag
+    revision_data = item_model.content
+    uid = item_model.uid
+
+    Model = models.CollectionItem
+
+    with transaction.atomic():
+        instance, created = Model.objects.get_or_create(
+            uid=uid, defaults=item_model.dict(exclude={"uid", "etag", "content"})
+        )
+        cur_etag = instance.etag if not created else None
+
+        # If we are trying to update an up to date item, abort early and consider it a success
+        if cur_etag == revision_data.uid:
+            return instance
+
+        if validate_etag and cur_etag != etag:
+            raise ValidationError(
+                "wrong_etag",
+                "Wrong etag. Expected {} got {}".format(cur_etag, etag),
+                status_code=status.HTTP_409_CONFLICT,
+            )
+
+        if not created:
+            # We don't have to use select_for_update here because the unique constraint on current guards against
+            # the race condition. But it's a good idea because it'll lock and wait rather than fail.
+            current_revision = instance.revisions.filter(current=True).select_for_update().first()
+            current_revision.current = None
+            current_revision.save()
+
+        try:
+            process_revisions_for_item(instance, revision_data)
+        except django_exceptions.ValidationError as e:
+            transform_validation_error("content", e)
+
+    return instance
+
+
+def item_bulk_common(data: ItemBatchIn, user: User, stoken: t.Optional[str], uid: str, validate_etag: bool):
     queryset = get_collection_queryset(user, default_queryset)
     with transaction.atomic():  # We need this for locking the collection object
         collection_object = queryset.select_for_update().get(uid=uid)
+
         if stoken is not None and stoken != collection_object.stoken:
             raise ValidationError("stale_stoken", "Stoken is too old", status_code=status.HTTP_409_CONFLICT)
 
+        # XXX-TOM: make sure we return compatible errors
+        data.validate_db()
+        for item in data.items:
+            item_create(item, validate_etag)
 
-def item_create():
-    pass  #
+        return MsgpackResponse({})
 
 
 @collection_router.post("/{uid}/item/transaction/")