Chats: Change id to flake id.

priv/repo/migrations/20200607112923_change_chat_id_to_flake.exs

@@ -0,0 +1,23 @@
+defmodule Pleroma.Repo.Migrations.ChangeChatIdToFlake do
+  use Ecto.Migration
+
+  def up do
+    execute("""
+    alter table chats
+    drop constraint chats_pkey cascade,
+    alter column id drop default,
+    alter column id set data type uuid using cast( lpad( to_hex(id), 32, '0') as uuid),
+    add primary key (id)
+    """)
+
+    execute("""
+    alter table chat_message_references
+    alter column chat_id set data type uuid using cast( lpad( to_hex(chat_id), 32, '0') as uuid),
+    add constraint chat_message_references_chat_id_fkey foreign key (chat_id) references chats(id) on delete cascade
+    """)
+  end
+
+  def down do
+    :ok
+  end
+end