Fix unique username constraint for local users not being enforced in database (#14099)

This should not be an issue in practice because of the Rails-level uniqueness
check, but local accounts having a NULL domain means the uniqueness constraint
did not apply to them (since no two NULL values are considered equal).

1 files changed, 15 insertions, 0 deletions

diff --git a/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb b/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb
new file mode 100644
index 000000000..c5688681f
--- /dev/null
+++ b/db/migrate/20200620164023_add_fixed_lowercase_index_to_accounts.rb
@@ -0,0 +1,15 @@
+class AddFixedLowercaseIndexToAccounts < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def up
+    rename_index :accounts, 'index_accounts_on_username_and_domain_lower', 'old_index_accounts_on_username_and_domain_lower' unless index_name_exists?(:accounts, 'old_index_accounts_on_username_and_domain_lower')
+    add_index :accounts, "lower (username), COALESCE(lower(domain), '')", name: 'index_accounts_on_username_and_domain_lower', unique: true, algorithm: :concurrently
+    remove_index :accounts, name: 'old_index_accounts_on_username_and_domain_lower'
+  end
+
+  def down
+    add_index :accounts, 'lower (username), lower(domain)', name: 'old_index_accounts_on_username_and_domain_lower', unique: true, algorithm: :concurrently
+    remove_index :accounts, name: 'index_accounts_on_username_and_domain_lower'
+    rename_index :accounts, 'old_index_accounts_on_username_and_domain_lower', 'index_accounts_on_username_and_domain_lower'
+  end
+end