Criteria

Coming soon...

Finding the Pricey Parts: An Adventure in Methods

Alright, my fellow code-wranglers, let's imagine we're whizzing through space in our trusty starship. We've got this super handy $ship->getParts() method that gives us the low-down on every piece of kit on our vessel. But what if we're not interested in the cheap nuts and bolts? What if we want to know about the high-end stuff, the parts that cost more than 50,000 credits?

Sure, we could do a fresh query in our controller for all the starship parts related to the ship where the price is greater than 50,000. But where's the fun in that? Let's stick with our trusty $ship->getParts() methods. They're as easy as pie, and I do love me some pie.

The Birth of getExpensiveParts()

Jump into the Starship class and look for the getParts method. I'm going to copy that method, paste it right below, and rename it to getExpensiveParts(). For now, let's have it return all the parts.

Back on our show template, let's take this baby for a spin. Change 'parts' to 'expensive parts' and then call $ship->getExpensiveParts(). Even though there's no expensiveParts property, it's going to call the getExpensiveParts() method we just crafted.

Filtering Out the Cheap Stuff

Now let's make our new method return only the expensive parts. Remember, $this->parts isn't an array – it's a special collection object with a few tricks up its sleeve. One of these is the filter() method. This nifty little function calls a callback for every single part. If we return true, it includes that part in the final collection. If we return false, it filters it out. So we can just say return $part->getPrice() > 50000;.

However, this isn't the most efficient way to do things. We're still querying for every single part that relates to our starship, then filtering that in PHP. That's like trying to find a diamond in a coal mine. What we really want to do is change the query itself, so Doctrine grabs only the parts related to the starship where the price is greater than 50,000.

The Power of the Criteria Object

Enter the Criteria object. This thing is as mighty as a Wookiee, although I'll admit, it's a bit cryptic. Time to clear out our logic and instead use $criteria = Criteria::create()->andWhere(Criteria::expr()->gt('price', 50000));. To use this, we just say return $this->parts->matching($criteria); at the end.

Now, if you know me, you know I like to keep my query logic organized in my repository classes. But now we have some of our query logic inside our entity. Is that bad? Not necessarily, but I like to keep things tidy. So let's move this Criteria logic into our repository.

Moving Criteria to the Repository

Over to our StarshipPartRepository we go. Anywhere in here, add a public static function called createExpensiveCriteria(). Why static? Two reasons: one, because we can (we're not using the this variable anywhere inside of here), and two, because we're gonna use this method from the Starship entity. We can't auto-wire services into entities, so it has to be static.

Back in Starship, let's use this. Delete the Criteria stuff entirely, and instead say matching(StarshipPartRepository::createExpensiveCriteria()).

Combining Criteria with Query Builders

Everything still works like a charm. Let's go a step further and flex our developer muscles. Let's create a method to demonstrate how we can combine Criteria with Query Builders.

Let's say we want to get a list of all the expensive parts in some controller. Copy the getExpensiveParts() from our Starship, because it'll look exactly the same. Paste that in StarshipPartRepository.

To combine this with a Criteria, say addCriteria(self::createExpensiveCriteria()). Now that we're in a Query Builder, we can do the normal stuff here. So setMaxResults($limit). Want to do an orderBy or an andWhere? Go for it. And of course, you can finish this with getQuery()->getResult().

Combining Criteria with Query Builders is a power move.

Alright, that's enough thrill for one lesson. Next time, we'll dive into something completely different. Buckle up!