diff --git a/tildes/tildes/models/comment/comment.py b/tildes/tildes/models/comment/comment.py
index d305fa4..872a0e3 100644
--- a/tildes/tildes/models/comment/comment.py
+++ b/tildes/tildes/models/comment/comment.py
@@ -131,13 +131,9 @@ class Comment(DatabaseModel):
     ):
         """Create a new comment."""
         self.topic = topic
-        self.user_id = author.user_id
-        if parent_comment:
-            self.parent_comment_id = parent_comment.comment_id
-        else:
-            self.parent_comment_id = None
-
+        self.user = author
         self.markdown = markdown
+        self.parent_comment = parent_comment
 
         incr_counter("comments")
 
diff --git a/tildes/tildes/models/comment/comment_label.py b/tildes/tildes/models/comment/comment_label.py
index 35697df..9170cc3 100644
--- a/tildes/tildes/models/comment/comment_label.py
+++ b/tildes/tildes/models/comment/comment_label.py
@@ -58,8 +58,8 @@ class CommentLabel(DatabaseModel):
         reason: Optional[str] = None,
     ):
         """Add a new label to a comment."""
-        self.comment_id = comment.comment_id
-        self.user_id = user.user_id
+        self.comment = comment
+        self.user = user
         self.label = label
         self.weight = weight
         self.reason = reason
diff --git a/tildes/tildes/models/comment/comment_notification.py b/tildes/tildes/models/comment/comment_notification.py
index 1c1473f..68c34de 100644
--- a/tildes/tildes/models/comment/comment_notification.py
+++ b/tildes/tildes/models/comment/comment_notification.py
@@ -99,15 +99,15 @@ class CommentNotification(DatabaseModel):
 
         for user in users_to_mention:
             # prevent the user from mentioning themselves
-            if comment.user_id == user.user_id:
+            if comment.user == user:
                 continue
 
             if parent_comment:
                 # prevent comment replies from mentioning that comment's poster
-                if parent_comment.user_id == user.user_id:
+                if parent_comment.user == user:
                     continue
             # prevent top-level comments from mentioning the thread creator
-            elif comment.topic.user_id == user.user_id:
+            elif comment.topic.user == user:
                 continue
 
             mention_notification = cls(
diff --git a/tildes/tildes/models/message/message.py b/tildes/tildes/models/message/message.py
index f8c374e..50f4da6 100644
--- a/tildes/tildes/models/message/message.py
+++ b/tildes/tildes/models/message/message.py
@@ -111,9 +111,9 @@ class MessageConversation(DatabaseModel):
 
     def __init__(self, sender: User, recipient: User, subject: str, markdown: str):
         """Create a new message conversation between two users."""
-        self.sender_id = sender.user_id
-        self.recipient_id = recipient.user_id
-        self.unread_user_ids = [self.recipient_id]
+        self.sender = sender
+        self.recipient = recipient
+        self.unread_user_ids = [self.recipient.user_id]
         self.subject = subject
         self.markdown = markdown
         self.rendered_html = convert_markdown_to_safe_html(markdown)
@@ -231,12 +231,15 @@ class MessageReply(DatabaseModel):
     markdown: str = deferred(Column(Text, nullable=False))
     rendered_html: str = Column(Text, nullable=False)
 
+    conversation: MessageConversation = relationship(
+        "MessageConversation", innerjoin=True
+    )
     sender: User = relationship("User", lazy=False, innerjoin=True)
 
     def __init__(self, conversation: MessageConversation, sender: User, markdown: str):
         """Add a new reply to a message conversation."""
-        self.conversation_id = conversation.conversation_id
-        self.sender_id = sender.user_id
+        self.conversation = conversation
+        self.sender = sender
         self.markdown = markdown
         self.rendered_html = convert_markdown_to_safe_html(markdown)
 
diff --git a/tildes/tildes/models/topic/topic.py b/tildes/tildes/models/topic/topic.py
index 5af94b6..0931093 100644
--- a/tildes/tildes/models/topic/topic.py
+++ b/tildes/tildes/models/topic/topic.py
@@ -196,8 +196,8 @@ class Topic(DatabaseModel):
     def _create_base_topic(cls, group: Group, author: User, title: str) -> "Topic":
         """Create the "base" for a new topic."""
         new_topic = cls()
-        new_topic.group_id = group.group_id
-        new_topic.user_id = author.user_id
+        new_topic.group = group
+        new_topic.user = author
 
         # if the title is all caps, convert to title case
         if title.isupper():
diff --git a/tildes/tildes/models/user/user_invite_code.py b/tildes/tildes/models/user/user_invite_code.py
index 187a512..ca5133e 100644
--- a/tildes/tildes/models/user/user_invite_code.py
+++ b/tildes/tildes/models/user/user_invite_code.py
@@ -8,6 +8,7 @@ import string
 from datetime import datetime
 
 from sqlalchemy import CheckConstraint, Column, ForeignKey, Integer, Text, TIMESTAMP
+from sqlalchemy.orm import relationship
 from sqlalchemy.sql.expression import text
 
 from tildes.lib.string import separate_string
@@ -39,6 +40,8 @@ class UserInviteCode(DatabaseModel):
     )
     invitee_id: int = Column(Integer, ForeignKey("users.user_id"))
 
+    user: User = relationship("User", innerjoin=True, foreign_keys=[user_id])
+
     def __str__(self) -> str:
         """Format the code into a more easily readable version."""
         return separate_string(self.code, "-", 5)
@@ -49,7 +52,7 @@ class UserInviteCode(DatabaseModel):
         Note that uniqueness is not confirmed here, so there is the potential to create
         duplicate codes (which will fail to commit to the database).
         """
-        self.user_id = user.user_id
+        self.user = user
 
         code_chars = random.choices(self.ALPHABET, k=self.LENGTH)
         self.code = "".join(code_chars)