diff --git a/lib/matrix_server/room_server.ex b/lib/matrix_server/room_server.ex
index 4d489f3..9be1464 100644
--- a/lib/matrix_server/room_server.ex
+++ b/lib/matrix_server/room_server.ex
@@ -530,6 +530,7 @@ defmodule MatrixServer.RoomServer do
       room = Room.update_forward_extremities(event, room)
       event = Repo.insert!(event)
       state_set = StateResolution.resolve_forward_extremities(event)
+      # TODO: Do this as a background job, and not after every insert...
       _ = update_joined_rooms(room, state_set)
 
       {:ok, state_set, room}
@@ -539,7 +540,6 @@ defmodule MatrixServer.RoomServer do
   end
 
   # Update local accounts' room membership if applicable.
-  # TODO: Could be a background job.
   @spec update_joined_rooms(Room.t(), t()) :: JoinedRoom.t() | nil
   defp update_joined_rooms(%Room{id: room_id}, state_set) do
     server_name = MatrixServer.server_name()
@@ -553,19 +553,27 @@ defmodule MatrixServer.RoomServer do
         membership == "join"
       end)
 
-    joined_assocs =
-      Enum.map(joined, fn {{_, state_key}, _} ->
-        %{localpart: MatrixServer.get_localpart(state_key), room_id: room_id}
-      end)
+    map_localparts =
+      &Enum.map(&1, fn {{_, state_key}, _} -> MatrixServer.get_localpart(state_key) end)
 
-    not_joined_localparts =
-      Enum.map(not_joined, fn {{_, state_key}, _} -> MatrixServer.get_localpart(state_key) end)
+    joined_localparts = map_localparts.(joined)
+    not_joined_localparts = map_localparts.(not_joined)
 
-    _ = Repo.insert_all(JoinedRoom, joined_assocs, on_conflict: :nothing)
+    _ =
+      Repo.insert_all(
+        JoinedRoom,
+        from(a in Account,
+          where: a.localpart in ^joined_localparts,
+          select: %{account_id: a.id, room_id: ^room_id}
+        ),
+        on_conflict: :nothing
+      )
 
     Repo.delete_all(
       from jr in JoinedRoom,
-        where: jr.room_id == ^room_id and jr.localpart in ^not_joined_localparts
+        join: a in Account,
+        on: a.id == jr.account_id,
+        where: jr.room_id == ^room_id and a.localpart in ^not_joined_localparts
     )
   end
 end
diff --git a/lib/matrix_server/schema/account.ex b/lib/matrix_server/schema/account.ex
index b91f2bf..9cf703e 100644
--- a/lib/matrix_server/schema/account.ex
+++ b/lib/matrix_server/schema/account.ex
@@ -13,14 +13,14 @@ defmodule MatrixServer.Account do
 
   @max_mxid_length 255
 
-  @primary_key {:localpart, :string, []}
   schema "accounts" do
+    field :localpart, :string
     field :password_hash, :string, redact: true
-    has_many :devices, Device, foreign_key: :localpart
+    has_many :devices, Device
 
     many_to_many :joined_rooms, Room,
       join_through: JoinedRoom,
-      join_keys: [localpart: :localpart, room_id: :id]
+      join_keys: [account_id: :id, room_id: :id]
 
     timestamps(updated_at: false)
   end
@@ -50,31 +50,35 @@ defmodule MatrixServer.Account do
   Return an multi to register a new user.
   """
   @spec register(Register.t()) :: Multi.t()
-  def register(%Register{} = input) do
+  def register(input) do
+    localpart = input.username || MatrixServer.random_string(10, ?a..?z)
+
     account_params = %{
-      localpart: input.username || MatrixServer.random_string(10, ?a..?z),
+      localpart: localpart,
       password_hash: Bcrypt.hash_pwd_salt(input.password)
     }
 
     Multi.new()
     |> Multi.insert(:account, changeset(%Account{}, account_params))
     |> Multi.insert(:device, fn %{account: account} ->
+      device_id = input.device_id || Device.generate_device_id(account.localpart)
+      access_token = Device.generate_access_token(localpart, device_id)
+
       device_params = %{
         display_name: input.initial_device_display_name,
-        device_id: input.device_id || Device.generate_device_id(account.localpart)
+        device_id: device_id
       }
 
-      Ecto.build_assoc(account, :devices)
+      Ecto.build_assoc(account, :devices, access_token: access_token)
       |> Device.changeset(device_params)
     end)
-    |> Multi.run(:device_with_access_token, &Device.insert_new_access_token/2)
   end
 
   @doc """
   Return a function to log a user in.
   """
-  @spec login(Login.t()) :: (Ecto.Repo.t() -> {:error, any()} | {:ok, Device.t()})
-  def login(%Login{} = input) do
+  @spec login(Login.t()) :: (Ecto.Repo.t() -> {:error, any()} | {:ok, {Account.t(), Device.t()}})
+  def login(input) do
     localpart = try_get_localpart(input.identifier.user)
 
     fn repo ->
@@ -83,7 +87,7 @@ defmodule MatrixServer.Account do
           if Bcrypt.verify_pass(input.password, hash) do
             case Device.login(input, account) do
               {:ok, device} ->
-                device
+                {account, device}
 
               {:error, _cs} ->
                 repo.rollback(:forbidden)
@@ -119,7 +123,7 @@ defmodule MatrixServer.Account do
     |> validate_length(:password_hash, max: 60)
     |> validate_format(:localpart, MatrixServer.localpart_regex())
     |> validate_length(:localpart, max: localpart_length())
-    |> unique_constraint(:localpart, name: :accounts_pkey)
+    |> unique_constraint(:localpart, name: :accounts_localpart_index)
   end
 
   @spec localpart_length :: integer()
diff --git a/lib/matrix_server/schema/device.ex b/lib/matrix_server/schema/device.ex
index 1099f17..8d41a3c 100644
--- a/lib/matrix_server/schema/device.ex
+++ b/lib/matrix_server/schema/device.ex
@@ -4,43 +4,27 @@ defmodule MatrixServer.Device do
   import Ecto.{Changeset, Query}
 
   alias MatrixServer.{Account, Device, Repo}
-  alias MatrixServerWeb.Client.Request.Login
 
   @type t :: %__MODULE__{
           device_id: String.t(),
           access_token: String.t(),
           display_name: String.t(),
-          localpart: String.t()
+          account_id: integer()
         }
 
-  @primary_key false
   schema "devices" do
-    field :device_id, :string, primary_key: true
+    field :device_id, :string
     field :access_token, :string, redact: true
     field :display_name, :string
 
-    belongs_to :account, Account,
-      foreign_key: :localpart,
-      references: :localpart,
-      type: :string,
-      primary_key: true
+    belongs_to :account, Account
   end
 
   def changeset(device, params \\ %{}) do
     device
     |> cast(params, [:display_name, :device_id])
-    |> validate_required([:localpart, :device_id])
-    |> unique_constraint([:localpart, :device_id], name: :devices_pkey)
-  end
-
-  def insert_new_access_token(repo, %{
-        device: %Device{localpart: localpart, device_id: device_id} = device
-      }) do
-    access_token = generate_access_token(localpart, device_id)
-
-    device
-    |> change(%{access_token: access_token})
-    |> repo.update()
+    |> validate_required([:device_id])
+    |> unique_constraint([:device_id, :account_id], name: :devices_device_id_account_id_index)
   end
 
   def generate_access_token(localpart, device_id) do
@@ -52,9 +36,9 @@ defmodule MatrixServer.Device do
     "#{localpart}_#{System.os_time(:millisecond)}"
   end
 
-  def login(%Login{} = input, account) do
-    device_id = input.device_id || generate_device_id(account.localpart)
-    access_token = generate_access_token(account.localpart, device_id)
+  def login(input, %Account{localpart: localpart} = account) do
+    device_id = input.device_id || generate_device_id(localpart)
+    access_token = generate_access_token(localpart, device_id)
 
     update_query =
       from(d in Device)
@@ -75,6 +59,6 @@ defmodule MatrixServer.Device do
     Ecto.build_assoc(account, :devices)
     |> Device.changeset(device_params)
     |> put_change(:access_token, access_token)
-    |> Repo.insert(on_conflict: update_query, conflict_target: [:localpart, :device_id])
+    |> Repo.insert(on_conflict: update_query, conflict_target: [:account_id, :device_id])
   end
 end
diff --git a/lib/matrix_server/schema/joined_room.ex b/lib/matrix_server/schema/joined_room.ex
index b2e3584..aef884b 100644
--- a/lib/matrix_server/schema/joined_room.ex
+++ b/lib/matrix_server/schema/joined_room.ex
@@ -4,17 +4,13 @@ defmodule MatrixServer.JoinedRoom do
   alias MatrixServer.{Account, Room}
 
   @type t :: %__MODULE__{
-          localpart: String.t(),
+          account_id: integer(),
           room_id: String.t()
         }
 
   @primary_key false
   schema "joined_rooms" do
-    belongs_to :account, Account,
-      foreign_key: :localpart,
-      references: :localpart,
-      type: :string,
-      primary_key: true
+    belongs_to :account, Account, primary_key: true
 
     belongs_to :room, Room, primary_key: true, type: :string
   end
diff --git a/lib/matrix_server_web/client/controllers/login_controller.ex b/lib/matrix_server_web/client/controllers/login_controller.ex
index da47d51..eb6460a 100644
--- a/lib/matrix_server_web/client/controllers/login_controller.ex
+++ b/lib/matrix_server_web/client/controllers/login_controller.ex
@@ -4,7 +4,7 @@ defmodule MatrixServerWeb.Client.LoginController do
   import MatrixServerWeb.Error
   import Ecto.Changeset
 
-  alias MatrixServer.{Repo, Account}
+  alias MatrixServer.{Repo, Account, Device}
   alias MatrixServerWeb.Client.Request.Login
   alias Ecto.Changeset
 
@@ -38,11 +38,13 @@ defmodule MatrixServerWeb.Client.LoginController do
         input = apply_changes(cs)
 
         case Account.login(input) |> Repo.transaction() do
-          {:ok, device} ->
+          {:ok,
+           {%Account{localpart: localpart},
+            %Device{access_token: access_token, device_id: device_id}}} ->
             data = %{
-              user_id: MatrixServer.get_mxid(device.localpart),
-              access_token: device.access_token,
-              device_id: device.device_id
+              user_id: MatrixServer.get_mxid(localpart),
+              access_token: access_token,
+              device_id: device_id
             }
 
             conn
diff --git a/lib/matrix_server_web/client/controllers/register_controller.ex b/lib/matrix_server_web/client/controllers/register_controller.ex
index 48bc5a6..8411c78 100644
--- a/lib/matrix_server_web/client/controllers/register_controller.ex
+++ b/lib/matrix_server_web/client/controllers/register_controller.ex
@@ -4,7 +4,7 @@ defmodule MatrixServerWeb.Client.RegisterController do
   import MatrixServerWeb.Error
   import Ecto.Changeset
 
-  alias MatrixServer.{Repo, Account}
+  alias MatrixServer.{Repo, Account, Device}
   alias MatrixServerWeb.Client.Request.Register
   alias Ecto.Changeset
 
@@ -21,14 +21,18 @@ defmodule MatrixServerWeb.Client.RegisterController do
         input = apply_changes(cs)
 
         case Account.register(input) |> Repo.transaction() do
-          {:ok, %{device_with_access_token: device}} ->
-            data = %{user_id: MatrixServer.get_mxid(device.localpart)}
+          {:ok,
+           %{
+             account: %Account{localpart: localpart},
+             device: %Device{device_id: device_id, access_token: access_token}
+           }} ->
+            data = %{user_id: MatrixServer.get_mxid(localpart)}
 
             data =
               if not input.inhibit_login do
                 data
-                |> Map.put(:device_id, device.device_id)
-                |> Map.put(:access_token, device.access_token)
+                |> Map.put(:device_id, device_id)
+                |> Map.put(:access_token, access_token)
               else
                 data
               end
diff --git a/lib/matrix_server_web/client/controllers/room_controller.ex b/lib/matrix_server_web/client/controllers/room_controller.ex
index 4b68336..38f5a35 100644
--- a/lib/matrix_server_web/client/controllers/room_controller.ex
+++ b/lib/matrix_server_web/client/controllers/room_controller.ex
@@ -207,4 +207,14 @@ defmodule MatrixServerWeb.Client.RoomController do
   end
 
   def unban(conn, _), do: put_error(conn, :missing_param)
+
+  def send_message(%Conn{assigns: %{account: account}, body_params: body_params} = conn, %{
+        "room_id" => room_id,
+        "event_type" => event_type,
+        "txn_id" => txn_id
+      }) do
+    conn
+    |> send_resp(200, [])
+    |> halt()
+  end
 end
diff --git a/lib/matrix_server_web/router.ex b/lib/matrix_server_web/router.ex
index 1908588..7d37853 100644
--- a/lib/matrix_server_web/router.ex
+++ b/lib/matrix_server_web/router.ex
@@ -66,6 +66,7 @@ defmodule MatrixServerWeb.Router do
         post "/kick", RoomController, :kick
         post "/ban", RoomController, :ban
         post "/unban", RoomController, :unban
+        put "/send/:event_type/:txn_id", RoomController, :send_message
       end
     end
   end
diff --git a/priv/repo/migrations/20210830160818_create_initial_tables.exs b/priv/repo/migrations/20210830160818_create_initial_tables.exs
index cb2e2e8..b67cd55 100644
--- a/priv/repo/migrations/20210830160818_create_initial_tables.exs
+++ b/priv/repo/migrations/20210830160818_create_initial_tables.exs
@@ -2,12 +2,14 @@ defmodule MatrixServer.Repo.Migrations.CreateInitialTables do
   use Ecto.Migration
 
   def change do
-    create table(:accounts, primary_key: false) do
-      add :localpart, :string, primary_key: true, null: false
+    create table(:accounts) do
+      add :localpart, :string, null: false
       add :password_hash, :string, size: 60, null: false
       timestamps(updated_at: false)
     end
 
+    create index(:accounts, [:localpart], unique: true)
+
     create table(:rooms, primary_key: false) do
       add :state, {:array, {:array, :string}}, default: [], null: false
       add :forward_extremities, {:array, :string}, default: [], null: false
@@ -16,10 +18,7 @@ defmodule MatrixServer.Repo.Migrations.CreateInitialTables do
     end
 
     create table(:joined_rooms, primary_key: false) do
-      add :localpart,
-          references(:accounts, column: :localpart, type: :string),
-          primary_key: true,
-          null: false
+      add :account_id, references(:accounts), primary_key: true, null: false
 
       add :room_id, references(:rooms, type: :string),
         primary_key: true,
@@ -62,20 +61,16 @@ defmodule MatrixServer.Repo.Migrations.CreateInitialTables do
 
     create index(:aliases, [:room_id])
 
-    create table(:devices, primary_key: false) do
-      add :device_id, :string, primary_key: true, null: false
+    create table(:devices) do
+      add :device_id, :string, null: false
       add :access_token, :string
       add :display_name, :string
 
-      add :localpart,
-          references(:accounts, column: :localpart, on_delete: :delete_all, type: :string),
-          primary_key: true,
-          null: false
+      add :account_id, references(:accounts, on_delete: :delete_all), null: false
     end
 
-    # Compound primary already indexes device_id.
-    create index(:devices, [:localpart])
-
+    create index(:devices, [:device_id, :account_id], unique: true)
+    create index(:devices, [:account_id])
     create index(:devices, [:access_token], unique: true)
   end
 end