From 5dd2eeb87cddadadf6030b168892a2f56e3c8781 Mon Sep 17 00:00:00 2001
From: Benjamin Dauvergne <bdauvergne@entrouvert.com>
Date: Tue, 14 Sep 2021 21:03:16 +0200
Subject: [PATCH 2/3] migrate issuer data (#56819)

---
 mellon/migrations/0004_migrate_issuer.py | 31 ++++++++++++++
 tests/conftest.py                        | 51 ++++++++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 mellon/migrations/0004_migrate_issuer.py

diff --git a/mellon/migrations/0004_migrate_issuer.py b/mellon/migrations/0004_migrate_issuer.py
new file mode 100644
index 0000000..a09c996
--- /dev/null
+++ b/mellon/migrations/0004_migrate_issuer.py
@@ -0,0 +1,31 @@
+# Generated by Django 2.2.19 on 2021-09-14 18:54
+
+from django.db import migrations
+from django.db.models import Count
+
+
+def migrate_issuer_forward(apps, schema_editor):
+    UserSAMLIdentifier = apps.get_model('mellon', 'UserSAMLIdentifier')
+    Issuer = apps.get_model('mellon', 'Issuer')
+    issuers = UserSAMLIdentifier.objects.values_list('issuer').annotate(total=Count('id'))
+    for issuer, total in issuers:
+        issuer_instance = Issuer.objects.create(entity_id=issuer)
+        UserSAMLIdentifier.objects.filter(issuer=issuer).update(issuer_fk=issuer_instance)
+
+
+def migrate_issuer_backward(apps, schema_editor):
+    UserSAMLIdentifier = apps.get_model('mellon', 'UserSAMLIdentifier')
+    Issuer = apps.get_model('mellon', 'Issuer')
+    for issuer in Issuer.objects.all():
+        UserSAMLIdentifier.objects.filter(issuer_fk=issuer).update(isuer=issuer.entity_id)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('mellon', '0003_add_issuer_model'),
+    ]
+
+    operations = []
+    operations = [
+        migrations.RunPython(migrate_issuer_forward, migrate_issuer_backward),
+    ]
diff --git a/tests/conftest.py b/tests/conftest.py
index 2e668be..b8df92e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -18,6 +18,9 @@ import os
 
 import django_webtest
 import pytest
+from django.core.management import call_command
+from django.db import connection
+from django.db.migrations.executor import MigrationExecutor
 
 
 @pytest.fixture(autouse=True)
@@ -82,3 +85,51 @@ def metadata_path(tmpdir, metadata):
     with metadata_path.open('w') as fd:
         fd.write(metadata)
     yield str(metadata_path)
+
+
+@pytest.fixture()
+def migration(request, transactional_db):
+    # see https://gist.github.com/asfaltboy/b3e6f9b5d95af8ba2cc46f2ba6eae5e2
+    """
+    This fixture returns a helper object to test Django data migrations.
+    The fixture returns an object with two methods;
+     - `before` to initialize db to the state before the migration under test
+     - `after` to execute the migration and bring db to the state after the migration
+    The methods return `old_apps` and `new_apps` respectively; these can
+    be used to initiate the ORM models as in the migrations themselves.
+    For example:
+        def test_foo_set_to_bar(migration):
+            old_apps = migration.before([('my_app', '0001_inital')])
+            Foo = old_apps.get_model('my_app', 'foo')
+            Foo.objects.create(bar=False)
+            assert Foo.objects.count() == 1
+            assert Foo.objects.filter(bar=False).count() == Foo.objects.count()
+            # executing migration
+            new_apps = migration.apply([('my_app', '0002_set_foo_bar')])
+            Foo = new_apps.get_model('my_app', 'foo')
+
+            assert Foo.objects.filter(bar=False).count() == 0
+            assert Foo.objects.filter(bar=True).count() == Foo.objects.count()
+    Based on: https://gist.github.com/blueyed/4fb0a807104551f103e6
+    """
+
+    class Migrator:
+        def before(self, targets, at_end=True):
+            """Specify app and starting migration names as in:
+            before([('app', '0001_before')]) => app/migrations/0001_before.py
+            """
+            executor = MigrationExecutor(connection)
+            executor.migrate(targets)
+            executor.loader.build_graph()
+            return executor._create_project_state(with_applied_migrations=True).apps
+
+        def apply(self, targets):
+            """Migrate forwards to the "targets" migration"""
+            executor = MigrationExecutor(connection)
+            executor.migrate(targets)
+            executor.loader.build_graph()
+            return executor._create_project_state(with_applied_migrations=True).apps
+
+    yield Migrator()
+
+    call_command('migrate', verbosity=0)
-- 
2.33.0