polls: created backbone of models (#72)

app/models/comment.py

@@ -19,6 +19,9 @@ class Comment(Post):
         backref=backref('comments', lazy='dynamic'),
         foreign_keys=thread_id)
 
+    # Other fields populated automatically through relations:
+    #  <poll>   A poll attached to the comment (of class Poll)
+
     def __init__(self, author, text, thread):
         """
         Create a new Comment in a thread.

app/models/poll.py

@@ -0,0 +1,63 @@
+from app import db
+from enum import Enum
+from sqlalchemy.orm import backref
+
+
+class PollType(Enum):
+    """Polls types: single/multiple answers. Easier than inheritance"""
+    SINGLE = 1
+    MULTIPLE = 2
+
+
+class Poll(db.Model):
+    """Some poll, with different options"""
+
+    __tablename__ = 'poll'
+
+    # Unique ID
+    id = db.Column(db.Integer, primary_key=True)
+
+    # Owner comment
+    comment_id = db.Column(db.Integer, db.ForeignKey('comment.id'))
+    comment = db.relationship('Comment', uselist=False, back_populates="poll",
+        foreign_keys=thread_id)
+
+    # Type
+    type = db.Column(db.Enum(PollType))
+
+    # Title/question
+    title = db.Column(db.UnicodeText)
+
+    # End datetime
+    end = db.Column(db.DateTime)
+
+    # Choices
+    # We want a size-variable list of strings, or a dictionnary with
+    # key/values, depending on the poll type.
+    # As the data is likely to be adapted to the poll type, the PickleType
+    # seems to be appropriate. Same applies for PollAnswer.
+    choices = db.Column(db.PickleType)
+
+    # Other fields populated automatically through relations:
+    #  <answers>   The list of answers (of type PollAnswer)
+
+
+class PollAnswer(db.Model):
+    """An answer to a poll"""
+
+    __tablename__ = 'pollanswer'
+
+    # Unique ID
+    id = db.Column(db.Integer, primary_key=True)
+
+    # Poll
+    poll_id = db.Column(db.Integer, db.ForeignKey('poll.id'))
+    poll = db.relationship('Poll', back_populates="answers",
+        foreign_keys=poll_id)
+
+    # Author. Must be Member
+    author_id = db.Column(db.Integer, db.ForeignKey('member.id'))
+    author = db.relationship('Member', foreign_keys=author_id)
+
+    # Choice(s)
+    choices = db.Column(db.PickleType)