forum: improve model relationships (so that it works)

app/models/comment.py

@@ -5,13 +5,18 @@ class Comment(Post):
     __tablename__ = 'comment'
     __mapper_args__ = {'polymorphic_identity': __tablename__}
 
+    # ID of the associated Post object
     id = db.Column(db.Integer, db.ForeignKey('post.id'), primary_key=True)
 
     # Standalone properties
     text = db.Column(db.UnicodeText)
 
-    # Relationships
-    thread_id = db.Column(db.Integer, db.ForeignKey('thread.id'), nullable=False)
+    # Relations
+    thread_id = db.Column(db.Integer, db.ForeignKey('thread.id'),
+        nullable=False)
+    thread = db.relationship('Thread', backref='comments',
+        foreign_keys=thread_id)
+
     # attachement = db.relationship('Attachement', backref='comment')
 
     def __init__(self, author, text, thread):

app/models/forum.py

@@ -12,8 +12,10 @@ class Forum(db.Model):
 
     # Relationships
     parent_id = db.Column(db.Integer, db.ForeignKey('forum.id'), nullable=True)
-    sub_forums = db.relationship('Forum', backref='parent', lazy=True)
-    topics = db.relationship('Topic', backref='forum')
+    parent    = db.relationship('Forum', backref='sub_forums', remote_side=id,
+                    lazy=True)
+
+    # Also [topics] which is provided by a backref from the Topic class
 
     def __init__(self, name, description, priv_prefix):
         self.name = name

app/models/thread.py

@@ -6,21 +6,25 @@ from config import V5Config
 class Thread(Post):
     """ Some thread, such as a topic, program, tutorial """
 
+    # Foreign Post object ID
     __tablename__ = 'thread'
     id = db.Column(db.Integer, db.ForeignKey('post.id'), primary_key=True)
 
+    # Identify threads as a type of posts using the table name, and add a
+    # column to further discriminate types of threads
     thread_type = db.Column(db.String(20))
     __mapper_args__ = {
         'polymorphic_identity': __tablename__,
         'polymorphic_on': thread_type
     }
 
-    # Standalone properties
+    # Properties
     title = db.Column(db.Unicode(V5Config.THREAD_NAME_MAXLEN))
+    # Also a relation [comments] populated from the Comment class.
 
-    # Relationships
-    top_comment = db.Column(db.Integer, db.ForeignKey('comment.id'))
-    comments = db.relationship('Comment', backref='thread')
+    # Relations
+    top_comment_id = db.Column(db.Integer, db.ForeignKey('comment.id'))
+    top_comment    = db.relationship('Comment', foreign_keys=top_comment_id)
 
     def __init__(self, author, text, title):
         """ Create a Thread """

app/models/topic.py

@@ -9,6 +9,7 @@ class Topic(Thread):
 
     # Relationships
     forum_id = db.Column(db.Integer, db.ForeignKey('forum.id'), nullable=False)
+    forum    = db.relationship('Forum', backref='topics',foreign_keys=forum_id)
 
     def __init__(self, author, text, title, forum):
         """ Create a Topic """

migrations/versions/e3b140752719_improve_relations_for_threads_and_.py

@@ -0,0 +1,34 @@
+"""improve relations for threads and comments
+
+Revision ID: e3b140752719
+Revises: 794d44c2bef8
+Create Date: 2019-08-24 19:09:46.981771
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'e3b140752719'
+down_revision = '794d44c2bef8'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('thread', sa.Column('top_comment_id', sa.Integer(), nullable=True))
+    op.drop_constraint('thread_top_comment_fkey', 'thread', type_='foreignkey')
+    op.create_foreign_key(None, 'thread', 'comment', ['top_comment_id'], ['id'])
+    op.drop_column('thread', 'top_comment')
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('thread', sa.Column('top_comment', sa.INTEGER(), autoincrement=False, nullable=True))
+    op.drop_constraint(None, 'thread', type_='foreignkey')
+    op.create_foreign_key('thread_top_comment_fkey', 'thread', 'comment', ['top_comment'], ['id'])
+    op.drop_column('thread', 'top_comment_id')
+    # ### end Alembic commands ###