学说2 - 间接一对多关联

Question

After a lot of searching for indirect associations, I only came up with this question. What I'd like to know is the exact opposite of that question, so I'm building up on it. Given the same entities:

class Continent {
    /**
    * @ORM\Id
    * @ORM\Column(type="integer", name="id")
    * @ORM\GeneratedValue(strategy="IDENTITY")
    */
    private $id;

    /**
    * @ORM\OneToMany(targetEntity="AppBundle\Entity\Country", mappedBy="continent")
    */
    private $countries;
}


class Country {
    /**
    * @ORM\Id
    * @ORM\Column(type="integer", name="id")
    * @ORM\GeneratedValue(strategy="IDENTITY")
    */
    private $id;

    /**
    * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Continent", inversedBy="countries")
    * @ORM\JoinColumn(name="continent_id", referencedColumnName="id")
    */
    private $continent;

    /**
    * @ORM\OneToMany(targetEntity="AppBundle\Entity\City", mappedBy="country")
    */
    private $cities;
}

class City {
    /**
    * @ORM\Id
    * @ORM\Column(type="integer", name="id")
    * @ORM\GeneratedValue(strategy="IDENTITY")
    */
    private $id;

    /**
    * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Country", inversedBy="cities")
    * @ORM\JoinColumn(name="country_id", referencedColumnName="id")
    */
    private $country;
}

Is there any way to have a collection of all cities in a continent, without having to build a custom query every time, with a field in the same fashion as the countries collection, possibly via annotations or maybe dynamic mapping?

The only way I could think of is by overriding the find... methods in the Repository - which I'm not sure how exactly I could achieve adding the field - and then either looping over the countries and adding their cities to a new collection, or using a custom query entirely.

Answer 1

First a comment about your mapping. Your mapping is wrong here:

inversedBy="countries" not inversedBy="country" and probably you want a column named continent_id instead of continentt_id

/**
 * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Continent", inversedBy="countries")
 * @ORM\JoinColumn(name="continent_id", referencedColumnName="id")
 */
 private $continent;

And here it should be inversedBy="cities" not inversedBy="city":

/**
 * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Country", inversedBy="cities")
 * @ORM\JoinColumn(name="country_id", referencedColumnName="id")
 */
 private $country;

Consider using validation for your entity model, the validation tool that ships with doctrine ORM will help you to get these things correct.

---

You can get such a result set by inner joining the countries with a certain continent.

Inside your CityRepository:

use Doctrine\ORM\Query\Expr\Join;

//...

public function findCitiesByContinent($params){
    $queryBuilder = $this->createQueryBuilder('c')
        ->innerJoin('c.country', 'cc', Join::WITH, 'cc.continent = :continent')
        ->setParameter('continent', $params['continent']);

    $query = $queryBuilder->getQuery();
    return $query->getResult();
}

You can reuse the query and just pass a different value for continent to your $params array each time you want the cities for a different continent.

This code is not tested, but I think it should work. Just leave a comment if you run into issues while testing this.

---

You can also add methods like @Edwin suggested, but you have to realize that it will eagerly load all entities. This is killing for performance if you have a huge amount of rows in your tables (a lot of cities and countries). That is why a query in your repository would be better.

---

Alternatively you can do this inside your entities by using criteria and collection filtering. You can read on how to do this here in the documentation chapter 8.8. Filtering Collections

The advantage of using a filter is also well explained in the documentation:

If the collection has not been loaded from the database yet, the filtering API can work on the SQL level to make optimized access to large collections.