Migrate mistral task_type

In order to be able to get full info from the API for old tasks,
it is needed to get the type from the spec column to the type column.

The alternative was adding a release note explaining the inconsistency.

Change-Id: I48dd286f749ceb491ab32ee15af62a8db54acdc7

mistral/db/sqlalchemy/migration/alembic_migrations/versions/020_add_type_to_task_execution.py

@@ -26,8 +26,22 @@ revision = '020'
 down_revision = '019'
 
 from alembic import op
+from mistral.db.sqlalchemy import types as st
 import sqlalchemy as sa
 
+# A simple model of the task executions table with only the fields needed for
+# the migration.
+task_executions = sa.Table(
+    'task_executions_v2',
+    sa.MetaData(),
+    sa.Column('id', sa.String(36), nullable=False),
+    sa.Column(
+        'spec',
+        st.JsonMediumDictType()
+    ),
+    sa.Column('type', sa.String(10), nullable=True)
+)
+
 
 def upgrade():
 
@@ -35,3 +49,25 @@ def upgrade():
         'task_executions_v2',
         sa.Column('type', sa.String(length=10), nullable=True)
     )
+
+    session = sa.orm.Session(bind=op.get_bind())
+    values = []
+
+    for row in session.query(task_executions):
+        values.append({'id': row[0],
+                       'spec': row[1]})
+
+    with session.begin(subtransactions=True):
+        for value in values:
+            task_type = "ACTION"
+            if "workflow" in value['spec']:
+                task_type = "WORKFLOW"
+
+            session.execute(
+                task_executions.update().values(type=task_type).where(
+                    task_executions.c.id == value['id']
+                )
+            )
+
+    # this commit appears to be necessary
+    session.commit()