Allow querying for migrations by source_compute only

The existing filtering only allows source-or-dest querying, and for
evacuate we want to look for things only *from* our host.

Related to blueprint robustify-evacuate

Change-Id: I05dbc71e969bcb8f64e6aa3b979cc0ffc75c1205

nova/db/sqlalchemy/api.py

@@ -4444,6 +4444,9 @@ def migration_get_all_by_filters(context, filters):
         host = filters["host"]
         query = query.filter(or_(models.Migration.source_compute == host,
                                  models.Migration.dest_compute == host))
+    elif "source_compute" in filters:
+        host = filters['source_compute']
+        query = query.filter(models.Migration.source_compute == host)
     if "migration_type" in filters:
         migtype = filters["migration_type"]
         query = query.filter(models.Migration.migration_type == migtype)

nova/tests/unit/db/test_db_api.py

@@ -1291,6 +1291,15 @@ class MigrationTestCase(test.TestCase):
             hosts = [migration['source_compute'], migration['dest_compute']]
             self.assertIn(filters["host"], hosts)
 
+    def test_get_migrations_by_filters_source_compute(self):
+        filters = {'source_compute': 'host2'}
+        migrations = db.migration_get_all_by_filters(self.ctxt, filters)
+        self.assertEqual(2, len(migrations))
+        sources = [x['source_compute'] for x in migrations]
+        self.assertEqual(['host2', 'host2'], sources)
+        dests = [x['dest_compute'] for x in migrations]
+        self.assertEqual(['host1', 'host3'], dests)
+
     def test_migration_get_unconfirmed_by_dest_compute(self):
         # Ensure no migrations are returned.
         results = db.migration_get_unconfirmed_by_dest_compute(self.ctxt, 10,