Working on How to Migrate Users Into WordPress 3.0

I hope that WordPress will provide some automation to migrate users from WordPress 2.9.x and earlier to the soon-to-be-released WordPress 3.0 running multi-sites (this shouldn’t be an issue with WP3 running single sites). Unfortunately, I haven’t be able to find any definitive word about that. Since I don’t want to be caught with my proverbial pants down, I’ve been hacking together a little migration program. It’s still in WIP-form (Work-in-Progress), but so far things haven’t broken so that I’ve noticed.

WordPress (any version) maintains a blog’s user list in a database table named ‘wp_users’. Even when running in multi-site mode, the users from all of the sites are kept in one single ‘wp_users’ table. It’s when you start migrating existing sites into WP3 that things get interesting. The User_IDs from the old single-site blog will change just as soon as you append them into the new multi-site table. This messes up info on who authored posts, comments, and some plug-ins (such as forums) that deal with the user base. PLUS, you have to keep track of what blog or blogs users have signed onto (nevermind their permissions). So yeah, it’s a lot of fun.

When you add in the fact that while I used to be a programmer, I don’t do it a lot anymore; I’m not a WordPress coding guru; and some info is just plain badly-documented (if at all)…well, it turns everything into an interesting exercise.

So… my plan of attack:

1. Prep the tables. Create an empty site in WP3. Export the necessary tables. Table prefixes, site links, and uploaded file locations need to be updated before the tables can be imported into the new site in the db.
2. Find all of the new users that aren’t already in the database and add them (plus simple meta data). Use the new user_IDs to update post and comment user_ID fields.
3. Find all users that share login name and email addresses. Update the meta data for the new blog. Use the WP3 user_IDs to update post and comment user_ID fields.
4. Any other users will be flagged to be dealt with manually.
5. In a separate program: Update any plug-in user_ID references (e.g. for a Simple:Press forum).
6. Cross your fingers and think happy thoughts.

Initial tests have been very favorable. Some data will be lost in the process simply because a lot of meta data is difficult to trace to various programs and some codes that are stored aren’t obvious. The overriding goal is for users to still be able to log in and access their posts and comments. If other settings need to be reset, it’s a smaller price to pay, I think, than having to re-register and losing access to your previous contributions.

We’ll see what happens. I’m about done with “3” and “4”. There’s still some writing and a lot of testing yet to do before I’d risk this on a live site.

There’s a follow-up to this post that has the procedure I used when I did my migration. Beta: Migrate Users From One or More WP Blogs Into WordPress 3.0 Multi-site