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Reusing Queries with the Query Builder

Enough with all this SQL stuff. Remember the query builder I was raving about earlier? I promised that one of its benefits is that, with a query builder, you can re-use parts of a query. But we don't have any of that right now.

Open up CategoryRepository. We have three methods, and all of them repeat the same leftJoin() to cat.fortuneCookies and the addSelect():

... lines 1 - 14
public function findAllOrdered()
{
$qb = $this->createQueryBuilder('cat')
... line 18
->leftJoin('cat.fortuneCookies', 'fc')
->addSelect('fc');
... lines 21 - 23
}
... line 25
public function search($term)
{
return $this->createQueryBuilder('cat')
... lines 29 - 31
->leftJoin('cat.fortuneCookies', 'fc')
->addSelect('fc')
... lines 34 - 36
}
... line 38
public function findWithFortunesJoin($id)
{
return $this->createQueryBuilder('cat')
... line 42
->leftJoin('cat.fortuneCookies', 'fc')
->addSelect('fc')
... lines 45 - 47
}
... lines 49 - 50

Ah, duplication! When you see duplication like this - whether it's a WHERE, an ORDER BY or a JOIN - there's a simple solution. Just add a new private function and have it add this stuff to the query builder.

Query-modifying Functions

Create a private function called addFortuneCookieJoinAndSelect(), because that's what it's going to do! It'll accept a QueryBuilder as an argument. Our goal is to, well, add the join to that. So I'll copy the 2 pieces that we want, add a $qb, then paste it there. And just for convenience, let's return this too:

... lines 1 - 52
/**
* Joins over to cat.fortuneCookies AND selects its fields
*
* @param QueryBuilder $qb
* @return QueryBuilder
*/
private function addFortuneCookieJoinAndSelect(QueryBuilder $qb)
{
return $qb->leftJoin('cat.fortuneCookies', 'fc')
->addSelect('fc');
}
... lines 64 - 66

So, our function takes in a QueryBuilder, it modifies it, then it returns it so we can make any more changes. I'll be a nice programmer and add some PHPDoc.

Calling those Functions

The findAllOrdered() function is the one that fuels the homepage. So let's start here! Get rid of that duplicated leftJoin and addSelect. Instead, just call $this->addFortuneCookieJoinAndSelect() and pass it the $qb. So we create the query builder, do some things with it, but let our new function take care of the join stuff.

... lines 1 - 15
public function findAllOrdered()
{
$qb = $this->createQueryBuilder('cat')
->addOrderBy('cat.name', 'ASC');
$this->addFortuneCookieJoinAndSelect($qb);
$query = $qb->getQuery();
return $query->execute();
}
... lines 26 - 66

This should give us the exact same results. But you should never believe me, so let's go back and refresh the homepage. Yep, nice!

Now we get to celebrate by removing the rest of the duplication. So, addSelect and leftJoin should be gone. Instead of returning the result directly, we need to get a QueryBuilder first. So put $qb = in front and move the getQuery() stuff down and put the return in front of it. In the middle, call addFortuneCookieJoinAndSelect() like before:

... lines 1 - 26
public function search($term)
{
$qb = $this->createQueryBuilder('cat')
->andWhere('cat.name LIKE :searchTerm
OR cat.iconKey LIKE :searchTerm
OR fc.fortune LIKE :searchTerm');
$this->addFortuneCookieJoinAndSelect($qb);
return $qb
->setParameter('searchTerm', '%'.$term.'%')
->getQuery()
->execute();
}
... lines 40 - 66

And one more time in findWithFortunesJoin(). Remove the duplication, create a $qb variable, return the last part of the query, and stick our magic line in the middle::

... lines 1 - 39
public function findWithFortunesJoin($id)
{
$qb = $this->createQueryBuilder('cat')
->andWhere('cat.id = :id');
$this->addFortuneCookieJoinAndSelect($qb);
return $qb
->setParameter('id', $id)
->getQuery()
->getOneOrNullResult();
}
... lines 52 - 66

Try it! Refresh and click into a category. It all works. And you know, I feel a lot better. If there's one things I don't want to duplicate, it's query logic. I hope this looks really obvious to you - it's just a simple coding technique. But it's kind of amazing, because it's not something you can do easily with string queries. And it can really save you if once you've got complex WHERE clauses that need to be re-used. You don't want to screw that stuff up.

Leave a comment!

  • 2018-04-30 Victor Bocharsky

    Hey Fabian,

    We're sorry about it, I moderated that comment. Not sure why this angers Timothy so much :/

    Once again, I agree with you, and you have a good point. However, in practice, I think that's ok to use "and"/"or" when we're talking about 2 actions that do not exist without each other. Because in tests you need to test both of them and in a proper order too. Sometimes you can split into 2 private methods and call them from the public one, that makes sense if there's some complex logic and a lot of code for both actions.

    Cheers!

  • 2018-04-30 Fabian Picone

    Please? This is only my opinion in a discussion. I dont want to bash anyone. When you want more explanation then ask. This is really not constructive from you.
    Code smell is a used term, see https://en.wikipedia.org/wi.... Its bad to use "and" or "or" in the method name because, its confusing on writing test. When you want to test a method you describe e.g. "testAddFortuneCookieJoinAndSelect", namely you are saying to test two things. But you should test only one thing per once. So a method should do only one thing and describe only this thing in the name.

  • 2018-04-04 Victor Bocharsky

    Hey Fabian,

    Yes, I mostly agree with you, and in practice we do exactly this. But hey, this addFortuneCookieJoinAndSelect() method is so simple and has just one line of code ;)

    Cheers!

  • 2018-04-04 Fabian Picone

    When you want to do a couple of things in a method, the smell begins. So split the "things" out in single methods. A method should do only one thing. Its more testable.

  • 2018-04-03 Diego Aguiar

    Hey Fabian Picone

    Technically you are correct but sometimes you just want to do a couple of things in the same method, so I would say that that's ok to do it, but, you should refactor it as soon as you get one or two use cases that requires that action to be splitted.

    Cheers!

  • 2018-04-03 Fabian Picone

    UUh your code smells "addFortuneCookieJoinAndSelect". Never use "and" or "or" in Method names.

  • 2017-02-13 weaverryan

    Good call! It's one of those annoying times when there are TWO of a given class!

  • 2017-02-12 Peter Tsiampas

    One thing that happened to me, when I referenced the "QueryBuilder" and did the auto complete, it actually grabbed the DBAL one not the ORM one, just something to watch out for. :)

  • 2015-06-08 weaverryan

    Hey!

    I think that's fair - this could be said about any re-use: if you re-use less (e.g. keep code inside one function instead of creating another), then you can refactor that function later without side effects. If you abstract and call an outside function, then you indeed *do* need to be more careful when refactoring that private function. Of course, at least these are *private* - that drastically reduces the scope of places you need to look for side effects from changes :).

    Cheers!

  • 2015-06-05 spezia

    Hello,

    I noticed a problem here and I have a question. Can we imagine that we have 20 methods in this class? And all of them use this private method so we do not have duplication.
    And all works fine. But after 6 months, we need to change something, to remove something from private method. (better: a new developer needs to change this) So, we must look at every 20 methods and think whether it will cause an issue in 20 different places in app. I want to change only one method for 1 min without thinking whether I will break something in the rest of the application. So, this is my opinion.