Techniques to check if relationship exists in Doctrine2

I can't seem to find any mention in the Doctrine documentation on how to check if an entity has an existing relationship to another entity:

http://www.doctrine-project.org/docs/orm/2.0/en/reference/working-with-associations.html

In Doctrine 1.x there was a method called exists that could be called on开发者_如何学编程 an entity to check this:

http://www.doctrine-project.org/documentation/manual/1_2/en/working-with-models#dealing-with-relations:clearing-related-records

In Doctrine 2.0 this is what I've tended to do. What techniques are other people using?

<?php

class Group    {
    private $id;
    protected $name;
    protected $users;

    public function __construct()
    {
        $this->colorgroups = new ArrayCollection();
    }

    public function hasUsers() {
        return count($this->users) > 0;
    } 
}

---

Well - I actually stumbled on the correct answer today while looking though the ArrayCollection class. You should use the 'isEmpty' method.

From the code (the comments are theirs, not mine)

/**
 * Checks whether the collection is empty.
 * 
 * Note: This is preferrable over count() == 0.
 *
 * @return boolean TRUE if the collection is empty, FALSE otherwise.
 */
public function isEmpty()
{
    return ! $this->_elements;
}

So from my example

public function hasUsers() {
        return !$this->users->isEmpty();
} 

---

Doctrine2 uses different architecture than Doctrine1.2. If you want to check whether a group has a certain user associated with it you should write a method hasUser(User $user) that will determine it:

public function hasUser(User $user) {
    foreach ($this->users as $u) {
        if ($u->equals($user)) {
            return true;
        }
    }

    return false;
}

If you want to check whether a relationship is persisted in database you will have to execute a the following DQL query:

SELECT 1 FROM MyProject\Entity\Group g WHERE :user MEMBER OF g.users;

Where :user is User object.

---

You can use Exists method http://www.doctrine-project.org/api/common/2.4/class-Doctrine.Common.Collections.ArrayCollection.html#_exists something like this

$someId = 123;
$p = function($key, $element) use ($someId){
     return $element->getId() == $someId;
};

$u->exists($p); //here is your result

---

Alternatively you can use Exception handling

try {

$entity = $entity->getAnotherEntity() ; // OneToOne Mapping 

}catch(\Exception $e) {

$entity = null ;

}

P.S More specific exception can be used to make it even better .

---

I know this is an old question, but it could be useful to someone else or maybe even to you. I think what you were looking for was the relatedExists() method that you can find here: http://docs.doctrine-project.org/projects/doctrine1/en/latest/en/manual/working-with-models.html#clearing-related-records

Hope it will be useful!