Store history of a comment when editing

At the moment it is possible to edit comments via the API, but this
causes the previous content of the comment to be permanently lost.

This commit fixes this problem by keeping a record of the previous version
of a comment each time it is edited.

Change-Id: I0bcf4ba3555c8d96e91497742f424056e3123312

storyboard/db/api/comments.py

@@ -26,6 +26,12 @@ def comment_create(values):
 
 
 def comment_update(comment_id, values):
+    comment = api_base.entity_get(models.Comment, comment_id)
+    old_dict = {
+        'comment_id': comment_id,
+        'content': comment.content
+    }
+    api_base.entity_create(models.HistoricalComment, old_dict)
     return api_base.entity_update(models.Comment, comment_id, values)
 
 

storyboard/db/migration/alembic_migrations/versions/059_add_a_table_for_comment_history.py

@@ -0,0 +1,49 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+#
+
+"""Add a table for comment history
+
+Revision ID: 059
+Revises: 058
+Create Date: 2016-06-21 14:00:20.515139
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '059'
+down_revision = '058'
+
+
+from alembic import op
+import sqlalchemy as sa
+
+from storyboard.db.decorators import UTCDateTime
+from storyboard.db.models import MYSQL_MEDIUM_TEXT
+
+
+def upgrade(active_plugins=None, options=None):
+    op.create_table(
+        'comments_history',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('created_at', UTCDateTime(), nullable=True),
+        sa.Column('updated_at', UTCDateTime(), nullable=True),
+        sa.Column('content', MYSQL_MEDIUM_TEXT, nullable=True),
+        sa.Column('comment_id', sa.Integer(), nullable=False),
+        sa.ForeignKeyConstraint(['comment_id'], ['comments.id'],
+                                name='fk_comment_id'),
+        sa.PrimaryKeyConstraint('id')
+    )
+
+
+def downgrade(active_plugins=None, options=None):
+    op.drop_table('comments_history')

storyboard/db/models.py

@@ -508,6 +508,15 @@ class Comment(FullText, ModelBuilder, Base):
     parent = relationship('Comment', remote_side=[id], backref='children')
 
 
+class HistoricalComment(FullText, ModelBuilder, Base):
+    __tablename__ = 'comments_history'
+    __fulltext_columns__ = ['content']
+
+    content = Column(MYSQL_MEDIUM_TEXT)
+    comment_id = Column(Integer, ForeignKey('comments.id'), nullable=False)
+    current = relationship(Comment, backref='history')
+
+
 # Subscription and notifications
 
 class Subscription(ModelBuilder, Base):