diff --git a/alembic/versions/2023_03_19_1509-caf39c6e55fc_in_out_models.py b/alembic/versions/2023_03_19_1509-caf39c6e55fc_in_out_models.py
index 86a0cd1..fc759e4 100644
--- a/alembic/versions/2023_03_19_1509-caf39c6e55fc_in_out_models.py
+++ b/alembic/versions/2023_03_19_1509-caf39c6e55fc_in_out_models.py
@@ -31,6 +31,7 @@ def upgrade() -> None:
     sa.Column('ap_context', sa.String(), nullable=True),
     sa.Column('ap_published_at', sa.DateTime(timezone=True), nullable=False),
     sa.Column('ap_object', sa.JSON(), nullable=False),
+    sa.Column('activity_object_ap_id', sa.String(), nullable=True),
     sa.Column('visibility', sa.Enum('PUBLIC', 'UNLISTED', 'FOLLOWERS_ONLY', 'DIRECT', name='visibilityenum'), nullable=False),
     sa.Column('relates_to_inbox_object_id', sa.Integer(), nullable=True),
     sa.Column('relates_to_outbox_object_id', sa.Integer(), nullable=True),
@@ -41,6 +42,7 @@ def upgrade() -> None:
     )
     op.create_index(op.f('ix_inbox_ap_id'), 'inbox', ['ap_id'], unique=True)
     op.create_index(op.f('ix_inbox_ap_type'), 'inbox', ['ap_type'], unique=False)
+    op.create_index(op.f('ix_inbox_activity_object_ap_id'), 'inbox', ['activity_object_ap_id'], unique=False)
     op.create_index(op.f('ix_inbox_id'), 'inbox', ['id'], unique=False)
     op.create_table('outbox',
     sa.Column('id', sa.Integer(), nullable=False),
diff --git a/app/models.py b/app/models.py
index 29ee1bb..3b8029f 100644
--- a/app/models.py
+++ b/app/models.py
@@ -61,6 +61,7 @@ class InboxObject(Base):
     ap_context = Column(String, nullable=True)
     ap_published_at = Column(DateTime(timezone=True), nullable=False)
     ap_object: Mapped[dict[str, Any]] = Column(JSON, nullable=False) # type: ignore
+    activity_object_ap_id = Column(String, nullable=True, index=True)
 
     visibility = Column(Enum(ap.VisibilityEnum), nullable=False)
 
@@ -71,7 +72,7 @@ class InboxObject(Base):
     )
     relates_to_inbox_object: Mapped[Optional["InboxObject"]] = relationship(
         "InboxObject",
-        foreign_keys=relates_to_inbox_object_id,
+        foreign_keys=[relates_to_inbox_object_id],
         remote_side=id,
         uselist=False,
     )
@@ -82,8 +83,7 @@ class InboxObject(Base):
     )
     relates_to_outbox_object: Mapped[Optional["OutboxObject"]] = relationship(
         "OutboxObject",
-        foreign_keys=[relates_to_outbox_object_id],
-        remote_side=id,
+        foreign_keys=relates_to_outbox_object_id,
         uselist=False,
     )
 
@@ -117,7 +117,7 @@ class OutboxObject(Base):
     )
     relates_to_inbox_object: Mapped[Optional["InboxObject"]] = relationship(
         "InboxObject",
-        foreign_keys=[relates_to_inbox_object_id],
+        foreign_keys=relates_to_inbox_object_id,
         uselist=False,
     )
     relates_to_outbox_object_id = Column(