From a637c8eb92007c33704f90bcf61c60c6125556d3 Mon Sep 17 00:00:00 2001
From: Rebecca Law <rebecca.law@digital.cabinet-office.gov.uk>
Date: Tue, 20 Apr 2021 13:42:20 +0100
Subject: [PATCH 1/2] Add unique key on annual_billing for service_id +
 financial_year_start.

This is an extra precaution for the table to ensure data integrity. Since we only update/insert the data using the annual_billing_dao methods the integrity is in tact. I've check the data on preview, staging and prod there are no violations of this unique key.
---
 app/dao/annual_billing_dao.py                 |  2 +-
 app/models.py                                 |  3 +++
 .../0351_unique_key_annual_billing.py         | 22 +++++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 migrations/versions/0351_unique_key_annual_billing.py

diff --git a/app/dao/annual_billing_dao.py b/app/dao/annual_billing_dao.py
index 9497b0d75..ffad11ade 100644
--- a/app/dao/annual_billing_dao.py
+++ b/app/dao/annual_billing_dao.py
@@ -102,7 +102,7 @@ def set_default_free_allowance_for_service(service, year_start=None):
                                 f"{default_free_sms_fragment_limits['other'][year_start]}")
         free_allowance = default_free_sms_fragment_limits['other'][year_start]
 
-    dao_create_or_update_annual_billing_for_year(
+    return dao_create_or_update_annual_billing_for_year(
         service.id,
         free_allowance,
         year_start
diff --git a/app/models.py b/app/models.py
index 9d0db0563..2b91d9395 100644
--- a/app/models.py
+++ b/app/models.py
@@ -579,6 +579,9 @@ class AnnualBilling(db.Model):
     UniqueConstraint('financial_year_start', 'service_id', name='ix_annual_billing_service_id')
     service = db.relationship(Service, backref=db.backref("annual_billing", uselist=True))
 
+    __table_args__ = (UniqueConstraint(
+        'service_id', 'financial_year_start', name='uix_service_id_financial_year_start'),)
+
     def serialize_free_sms_items(self):
         return {
             'free_sms_fragment_limit': self.free_sms_fragment_limit,
diff --git a/migrations/versions/0351_unique_key_annual_billing.py b/migrations/versions/0351_unique_key_annual_billing.py
new file mode 100644
index 000000000..2f814b815
--- /dev/null
+++ b/migrations/versions/0351_unique_key_annual_billing.py
@@ -0,0 +1,22 @@
+"""
+
+Revision ID: 0351_unique_key_annual_billing
+Revises: 0350_update_rates
+Create Date: 2021-04-12 09:02:45.098875
+
+"""
+from alembic import op
+
+revision = '0351_unique_key_annual_billing'
+down_revision = '0350_update_rates'
+
+
+def upgrade():
+    op.create_unique_constraint(
+        'uix_service_id_financial_year_start', 'annual_billing', ['service_id', 'financial_year_start']
+    )
+
+
+def downgrade():
+    op.drop_constraint('uix_service_id_financial_year_start', 'annual_billing', type_='unique')
+

From 490efad97a00f1473251b0fce1f76d3b5ce2b3d4 Mon Sep 17 00:00:00 2001
From: Rebecca Law <rebecca.law@digital.cabinet-office.gov.uk>
Date: Fri, 23 Apr 2021 15:08:23 +0100
Subject: [PATCH 2/2] To avoid any table locks and contention on the production
 database we are going to add the unique index concurrently. This only works
 if we execute a commit first.

---
 .../versions/0351_unique_key_annual_billing.py | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/migrations/versions/0351_unique_key_annual_billing.py b/migrations/versions/0351_unique_key_annual_billing.py
index 2f814b815..288b18395 100644
--- a/migrations/versions/0351_unique_key_annual_billing.py
+++ b/migrations/versions/0351_unique_key_annual_billing.py
@@ -5,16 +5,28 @@ Revises: 0350_update_rates
 Create Date: 2021-04-12 09:02:45.098875
 
 """
+import os
+
 from alembic import op
 
 revision = '0351_unique_key_annual_billing'
 down_revision = '0350_update_rates'
 
+environment = os.environ['NOTIFY_ENVIRONMENT']
+
 
 def upgrade():
-    op.create_unique_constraint(
-        'uix_service_id_financial_year_start', 'annual_billing', ['service_id', 'financial_year_start']
-    )
+    index = """
+        CREATE UNIQUE INDEX CONCURRENTLY uix_service_id_financial_year_start 
+        ON annual_billing (service_id, financial_year_start)
+    """
+    constraint = """
+        ALTER TABLE annual_BILLING add constraint uix_service_id_financial_year_start
+         UNIQUE USING INDEX uix_service_id_financial_year_start
+    """
+    op.execute('COMMIT')
+    op.execute(index)
+    op.execute(constraint)
 
 
 def downgrade():