Fix foreign key and primary key errors in db scripts

Starting from 10.1.x of MariaDB and 5.6 of MySQL, they not allow
changes to primary key and foreign key columns after the definitions
creation. This breaks db alembic scripts with
IntegrityError constraints.

Fix db scripts to drop the foreign key constraint and add them back
once the definitions are modified in existing schemas.

Change-Id: I4a4faa1e6d0aafc26f2a56986f83c4c4f0cfc763
Closes-Bug: #1594807

tacker/db/migration/__init__.py

@@ -13,7 +13,9 @@
 #    under the License.
 
 from alembic import op
+import contextlib
 import sqlalchemy as sa
+from sqlalchemy.engine import reflection
 
 
 def alter_enum(table, column, enum_type, nullable):
@@ -35,3 +37,38 @@ def alter_enum(table, column, enum_type, nullable):
     else:
         op.alter_column(table, column, type_=enum_type,
                         existing_nullable=nullable)
+
+
+def create_foreign_key_constraint(table_name, fk_constraints):
+    for fk in fk_constraints:
+        op.create_foreign_key(
+            constraint_name=fk['name'],
+            source_table=table_name,
+            referent_table=fk['referred_table'],
+            local_cols=fk['constrained_columns'],
+            remote_cols=fk['referred_columns'],
+            ondelete=fk['options'].get('ondelete')
+        )
+
+
+def drop_foreign_key_constraint(table_name, fk_constraints):
+    for fk in fk_constraints:
+        op.drop_constraint(
+            constraint_name=fk['name'],
+            table_name=table_name,
+            type_='foreignkey'
+        )
+
+
+@contextlib.contextmanager
+def modify_foreign_keys_constraint(table_names):
+    inspector = reflection.Inspector.from_engine(op.get_bind())
+    try:
+        for table in table_names:
+            fk_constraints = inspector.get_foreign_keys(table)
+            drop_foreign_key_constraint(table, fk_constraints)
+        yield
+    finally:
+        for table in table_names:
+            fk_constraints = inspector.get_foreign_keys(table)
+            create_foreign_key_constraint(table, fk_constraints)

tacker/db/migration/alembic_migrations/versions/12a57080b278_alter_devices.py

@@ -27,17 +27,19 @@ down_revision = '12a57080b277'
 
 from alembic import op
 from sqlalchemy.dialects import mysql
+from tacker.db import migration
 
 
 def upgrade(active_plugins=None, options=None):
     # commands auto generated by Alembic - please adjust! #
-    op.alter_column(u'deviceattributes', 'device_id',
-                    existing_type=mysql.VARCHAR(length=255),
-                    nullable=False)
-    op.alter_column(u'devices', 'status',
-                    existing_type=mysql.VARCHAR(length=255),
-                    nullable=False)
-    # end Alembic commands #
+    fk_constraint = ('deviceattributes', )
+    with migration.modify_foreign_keys_constraint(fk_constraint):
+        op.alter_column(u'deviceattributes', 'device_id',
+                        existing_type=mysql.VARCHAR(length=255),
+                        nullable=False)
+    op.alter_column(u'devices', 'status', existing_type=mysql.VARCHAR(
+        length=255), nullable=False)
+    # end Alembic commands #s
 
 
 def downgrade(active_plugins=None, options=None):

tacker/db/migration/alembic_migrations/versions/f958f58e5daa_uuid_consistency.py

@@ -28,28 +28,35 @@ down_revision = 'acf941e54075'
 
 from alembic import op
 
+from tacker.db import migration
 from tacker.db import types
 
+FK_MAP = {'vims': ('vimauths', 'devices'), 'devices': ('deviceattributes',
+          'proxymgmtports'), 'devicetemplates': ('devices', 'servicetypes',
+                                                 'devicetemplateattributes')}
+
 
 def upgrade(active_plugins=None, options=None):
-    for table in ['vims', 'vimauths', 'devices', 'deviceattributes',
+
+    pk_id_tables = ('vims', 'vimauths', 'devices', 'deviceattributes',
                   'servicetypes', 'devicetemplates',
-                  'devicetemplateattributes']:
-        op.alter_column(table,
-                        'id',
-                        type_=types.Uuid)
+                  'devicetemplateattributes')
+    for table in pk_id_tables:
+        with migration.modify_foreign_keys_constraint(FK_MAP.get(table, [])):
+                op.alter_column(table, 'id', type_=types.Uuid)
 
-    for table in ['devices', 'servicetypes', 'devicetemplateattributes']:
-        op.alter_column(table,
-                        'template_id',
-                        type_=types.Uuid)
+    fk_template_id_tables = ('devices', 'servicetypes',
+                             'devicetemplateattributes')
+    for table in fk_template_id_tables:
+        with migration.modify_foreign_keys_constraint(fk_template_id_tables):
+            op.alter_column(table, 'template_id', type_=types.Uuid)
 
-    for table in ['devices', 'vimauths']:
-        op.alter_column(table,
-                        'vim_id',
-                        type_=types.Uuid)
+    fk_vim_id_tables = ('devices', 'vimauths')
+    for table in fk_vim_id_tables:
+        with migration.modify_foreign_keys_constraint(fk_vim_id_tables):
+            op.alter_column(table, 'vim_id', type_=types.Uuid)
 
-    for table in ['deviceattributes', 'proxymgmtports']:
-        op.alter_column(table,
-                        'device_id',
-                        type_=types.Uuid)
+    fk_device_id_tables = ('deviceattributes', 'proxymgmtports')
+    for table in fk_device_id_tables:
+        with migration.modify_foreign_keys_constraint(fk_device_id_tables):
+            op.alter_column(table, 'device_id', type_=types.Uuid)