feat: Make email ID's case insensitive (#5728)

* Database migration for deleting upper case emails and using email as an index

* Database migration to update deleted_at time
for repeated emails

* Updated migration

* Updated migrations

* Correct sql query.

* Sql query to undelete users

migrations/versions/7bb5891a9f2e_lowercase_email.py

@@ -0,0 +1,35 @@
+"""lowercase_email
+
+Revision ID: 7bb5891a9f2e
+Revises: 6e5c574cbfb8
+Create Date: 2019-03-30 12:51:48.134800
+
+"""
+
+from alembic import op
+from sqlalchemy import func
+import sqlalchemy as sa
+import sqlalchemy_utils
+
+
+# revision identifiers, used by Alembic.
+revision = '7bb5891a9f2e'
+down_revision = '6e5c574cbfb8'
+
+
+def upgrade():
+    op.execute("UPDATE users SET deleted_at = current_timestamp, _email = concat(_email, '_') where _email not in (SELECT DISTINCT ON (upper(_email)) _email FROM users);",
+               execution_options=None)
+    op.execute("create extension citext;",
+               execution_options=None)
+    op.execute("alter table users alter column _email type citext;",
+               execution_options=None)
+
+
+def downgrade():
+    op.execute("alter table users alter column _email type text;",
+               execution_options=None)
+    op.execute("UPDATE users SET deleted_at = null, _email = left(_email, length(_email)-1) where right(_email, 1) = '_';",
+               execution_options=None)
+    op.execute("drop extension citext;",
+               execution_options=None)