Rework migration 1679b5bc102c to not use the db api

This commit reworks the data migration to split microseconds from
the time column into the separate microseconds column as to not
rely on the DB api. For sqlite and postgres this causes potential
issues when we try to modify the schema for the test_runs table
when this migration is run because the models don't match the state
of the DB when this migration is run. MySQL is unaffected by this
potential issue because it runs the migration separately in
hand written sql.

Change-Id: I527e2ab9d030be639954fdb63584c3c4c6f4dd1c

subunit2sql/migrations/versions/1679b5bc102c_add_subsecond_columns_to_test_runs_table.py

@@ -29,12 +29,8 @@ import os
 from alembic import context
 from alembic import op
 from oslo_config import cfg
-from oslo_db.sqlalchemy import utils as db_utils
 import sqlalchemy as sa
 
-from subunit2sql.db import api as db_api
-from subunit2sql.db import models
-
 
 CONF = cfg.CONF
 
@@ -54,17 +50,19 @@ def upgrade():
         op.add_column('test_runs', sa.Column('stop_time_microsecond',
                                              sa.Integer(), default=0))
         if not CONF.disable_microsecond_data_migration:
-            session = db_api.get_session()
-            query = db_utils.model_query(models.TestRun, session).values(
-                models.TestRun.id, models.TestRun.start_time,
-                models.TestRun.stop_time)
-            for test_run in query:
-                start_micro = test_run[1].microsecond
-                stop_micro = test_run[2].microsecond
+            bind = op.get_bind()
+            metadata = sa.schema.MetaData()
+            metadata.bind = bind
+            test_runs = sa.Table('test_runs', metadata, autoload=True)
+            res = test_runs.select().execute()
+            for test_run in res:
+                start_micro = test_run[4].microsecond
+                stop_micro = test_run[5].microsecond
                 values = {'start_time_microsecond': start_micro,
                           'stop_time_microsecond': stop_micro}
-                db_api.update_test_run(values, test_run[0], session)
-            session.close()
+                op.execute(test_runs.update().where(
+                    test_runs.c.id == test_run[0]).values(values))
+            res.close()
 
 
 def downgrade():