Python script to merge comments from one wordpress instance to another

wp_merge_comments.py

#!/usr/bin/env python

# I recently had to merge the comments from an old instance of wordpress to 
# a new one (long and boring story).
# The posts had already been manually merged, but not the comments.

# So I wrote this script to merge the comments

# Warning: while this has worked (once) this may not be a good way to do it.
# Also, it is slow, so, for repeated operation, it creates a stats.json so it doesn't
# have to examine existing (or spam) comments twice. Make sure to remove it

from __future__ import print_function
import sqlalchemy as sa
from sqlalchemy import orm
import json

DB_SRC = "mysql://user:source@127.0.0.1:3307/wordpress"
DB_DEST = "mysql://user:dest@127.0.0.1/wordpress"

# from http://beerpla.net/2010/03/21/how-to-diagnose-and-fix-incorrect-post-comment-counts-in-wordpress/
fix_post_comment_count = """
UPDATE wp_posts wpp
LEFT JOIN
(SELECT comment_post_id AS c_post_id, count(*) AS cnt FROM wp_comments
 WHERE comment_approved = 1 GROUP BY comment_post_id) wpc
ON wpp.id=wpc.c_post_id
SET wpp.comment_count=wpc.cnt
WHERE wpp.post_type IN ('post', 'page')
      AND (wpp.comment_count!=wpc.cnt OR (wpp.comment_count != 0 AND wpc.cnt IS NULL));
"""

class WPDB:
    def __init__(self, url):
        self.engine = sa.create_engine(url)
        self.meta = sa.schema.MetaData()
        self.meta.reflect(bind=self.engine)
        self.wp_comments = self.meta.tables['wp_comments']
        self.wp_posts = self.meta.tables['wp_posts']
        self.session = orm.sessionmaker(bind=self.engine)()

def merge_comments():
    global existing_comments
    existing_comments = []
    found = 0
    count = 0

    source = WPDB(DB_SRC)
    dest = WPDB(DB_DEST)

    with open('stats.json', 'r') as f:
        existing_comments = json.load(f).get('existing_comments', [])

    for c_src in source.session.query(source.wp_comments):
        if c_src.comment_ID in existing_comments:
            continue

        # ignore pingbacks and spam
        if c_src.comment_type == 'pingback' or\
          c_src.comment_approved == 'spam':
            existing_comments.append(c_src.comment_ID)
            continue
        
        dest_exists = False
        count = count + 1
        p_src = source.session.query(source.wp_posts).\
          filter(source.wp_posts.c.ID == c_src.comment_post_ID).\
          first()
        # print(c_src.comment_author_email, c_src.comment_content,
        #      p_src.post_name)
        c_dest = dest.session.query(dest.wp_comments).\
          filter(dest.wp_comments.c.comment_author_email
                 == c_src.comment_author_email).\
          filter(dest.wp_comments.c.comment_author
                 == c_src.comment_author).\
          filter(dest.wp_comments.c.comment_author_url
                 == c_src.comment_author_url).\
          filter(dest.wp_comments.c.comment_content
                 == c_src.comment_content).\
          first()

        if c_dest:
            # sanity check that the post name is identical - we can't
            # go by post IDs
            p_dest = dest.session.query(dest.wp_posts).\
              filter(dest.wp_posts.c.ID == c_dest.comment_post_ID).\
              first()

            if p_src.post_name == p_dest.post_name:
                dest_exists = True
                existing_comments.append(c_src.comment_ID)
                found = found + 1
                print("comment %d exists in dest" % c_dest.comment_ID)

        if not dest_exists:
            p_dest_all = dest.session.query(dest.wp_posts).\
              filter(dest.wp_posts.c.post_name == p_src.post_name).\
              all()

            if len(p_dest_all) == 0:
                print("error: %d no post with title %s" %
                       (c_src.comment_ID, p_src.post_name))
            elif len(p_dest_all) > 1:
                print("error: comment %d more than one post (%d) with name %s" %
                       (c_src.comment_ID, len(p_dest_all), p_src.post_name))
            else:
                print("adding comment %s" % str(c_src))
                c_new = dest.wp_comments.insert(c_src)
                print("Adding to post %s: %s" % (c_src.post_name, str(c_new)))
                dest.engine.execute(c_new, comment_ID = None,
                                    comment_post_ID = p_dest_all[0].ID)
                
    print("found %d of %d comments" % (found, count))

    print("fixing post comment count")
    dest.engine.execute(fix_post_comment_count)

    return existing_comments

if __name__ == '__main__':

    try:
        merge_comments()
    finally:
        with open('stats.json', 'w') as f:
            json.dump({ 'existing_comments': existing_comments }, f)