Adding ORDER BY FIELD to Propel Criterias

Every now and then, we use Sphinx to provide full text searching in MySQL InnoDB tables. Sphinx is pretty solid. It’s easy to set up, pretty fast, and easy to deploy.

My one big issue with Sphinx has always been making it play nice with Symfony, specifically Propel. The way Sphinx returns a result set is as an ordered list of [id, weight] for each document it matched. As outlined here the idea is to then hit your MySQL server to return the actual documents and use “ORDER BY FIELD(id, [id list])” to keep them in the right order that you received the list.

The problem is, Propel Criteria objects provide no mechanism to set an ORDER BY FIELD. This is an issue because if you drop Criterias you loose Propel Pagers which generally adds to a lot of duplicated code and is honestly just not very elegant.

Anyway, after some thought I came up with this solution.

If you read through the definition of “Criteria::addDescendingOrderByColumn()”:

All it really does is add the second part of the ORDER BY clause to an array which then gets joined up to build the final SQL. Because of this, you can actually just add an element onto the orderByColumns array which will cause Propel to execute an ORDER BY FIELD SQL statement.

To make the magic happen, I sub-classed Criteria and then added a addOrderByField() function to let me add a field to order by as well as a list to order by.

8/8/12: Update per Simon’s comment below

Also add this function to make sure your ORDER BY FIELD columns get cleared:

To use it, do something like this:

And thats about it. Since sfCriteria is a sub-class of Criteria the code works seamlessly with existing PropelPagers and anything else that expects a Propel Criteria.

sfPropelPager and GROUP BY criteria

So for one reason or another (actually a few bad ones) I ended up having to use a Criteria object looking like this:

It makes SQL that looks something like this:

“SELECT tag_id, tag_model, id, COUNT(*) AS the_count FROM sf_tagging WHERE tag_id IN (1,2,3) GROUP BY taggable_model, taggable_id HAVING the_count > int”

The query sucks but whatever it works.

My issue came when I tried to use it with a sfPropelPager. I set up the pager per usual but for some reason the results that were coming back weren’t correct. For some reason, the COUNT being returned by the sfPropelPager was completely wrong. It turns out the offending lines are here in sfPropelPager.class.php :

For whatever reason, sfPropelPager clears the GROUP BY clauses before it calculates the COUNT for a criteria object. I’m not sure why it does this – but it certainly is unexpected and breaks my query in particular.

There are a handful of posts about this on the Symfony forums and it looks like the Propel people know about the issue to.

The solution to this is to use the setPeerCountMethod() from sfPropelPager. The setPeerCountMethod() function allows you to specify a custom COUNT() method inside the peer for your Criteria. I went ahead and added a new function to put the GROUP BY columns back in:

This solution works but it is extremely rigid. Since the custom count function has to be static you’d really be out of luck if you had variable columns or other dynamic requirements.

I’d love to know if someone has a cleaner/better/more elegant solution for this.

Propel and Primary keys

Today I was writing an administrator backend for a project we have. I had the code:

   foreach ($old_feeds as $old) $old->delete();

I was trying to remove some old foreign constraints before I deleted the main object, however, for the longest time the “$old” objects were not deleting, but no errors were being thrown. I did the usual debugging, added a die() statement inside the count, it was going there. I added a die statement in the foreach, it went there. I thought, “It must not be pulling the right ‘old’ objects.” I then added a $old->getName(); to see exactly what objects it was going through-they were the right ones. It made no sense. I next tired after the $old->delete();to add a $old->save();. The error I received was “You cannot save an object that has been deleted.” This didn’t make sense, since the object was still in the database. It hit me then, I had this problem in the past. Propel hates tables without primary keys. I quickly just added a simple primary key to the model, and the delete statements worked.

Moral: If dealing with Propel and you are getting some unexpected behavior, with zero errors, check to see if you have a primary key; it may save you hours of head banging.