model: index comments by thread for faster lookup

app/models/comment.py

@@ -15,7 +15,7 @@ class Comment(Post):
 
     # Parent thread
     thread_id = db.Column(db.Integer, db.ForeignKey('thread.id'),
-                          nullable=False)
+                          nullable=False, index=True)
     thread = db.relationship('Thread',
         backref=backref('comments', lazy='dynamic'),
         foreign_keys=thread_id)

migrations/versions/0abd1c81e3aa_index_coments_by_thread.py

@@ -0,0 +1,28 @@
+"""Index coments by thread
+
+Revision ID: 0abd1c81e3aa
+Revises: 44c2e37ef899
+Create Date: 2021-07-07 16:26:23.230696
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '0abd1c81e3aa'
+down_revision = '44c2e37ef899'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_index(op.f('ix_comment_thread_id'), 'comment', ['thread_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_comment_thread_id'), table_name='comment')
+    # ### end Alembic commands ###