How can I get access to ArrayCollection data inside my Array (Symfony 4)?

Question

fields table:

productgroup table:

In my Controller I load my fields_array like this:

$fields_array = $this->getDoctrine()->getRepository(class::fields)->findAll();

If fields and productgroup are not connected my fields_array looks like this:

array:2 [▼
  0 => Fields {#7460 ▼
    -id: 3
    -name: "cat"
    -unique_id: "5a38c820ed"
    -productgroup: PersistentCollection {#7464 ▼
      -snapshot: []
      -owner: Fields {#7460}
      -association: array:20 [ …20]
      -em: EntityManager {#2815 …11}
      -backRefFieldName: "fields"
      -typeClass: ClassMetadata {#6494 …}
      -isDirty: false
      #collection: ArrayCollection {#7465 ▼
        -elements: []
      }
      #initialized: false
    }
    -type: Type {#7541 ▶}
  }
  1 => Fields {#7542 ▼
    -id: 4
    -name: "horse"
    -unique_id: "bd7762b0e6"
    -productgroup: PersistentCollection {#7543 ▼
      -snapshot: []
      -owner: Fields {#7542}
      -association: array:20 [ …20]
      -em: EntityManager {#2815 …11}
      -backRefFieldName: "fields"
      -typeClass: ClassMetadata {#6494 …}
      -isDirty: false
      #collection: ArrayCollection {#7544 ▼ 
        -elements: []
      }
      #initialized: false
    }
    -type: Type {#7545 ▶}
  }
]

As you see the ArrayCollecton does not contain any elements.

So now I connect cat with the productgroup Animals. So my table fields_productgroup looks like this:

Now as you see, my ArrayCollection of cat contains the element Animals:

array:2 [▼
  0 => Fields {#7460 ▼
    -id: 3
    -name: "cat"
    -unique_id: "5a38c820ed"
    -productgroup: PersistentCollection {#7464 ▼
      -snapshot: array:1 [ …1]
      -owner: Fields {#7460}
      -association: array:20 [ …20]
      -em: EntityManager {#2815 …11}
      -backRefFieldName: "fields"
      -typeClass: ClassMetadata {#6494 …}
      -isDirty: false
      #collection: ArrayCollection {#7465 ▼
        -elements: array:1 [▼
          0 => Productgroup {#7146 ▼
            -id: 6
            -name: "Animals"
            -unique_id: "9e4ef1c46f"
            -fields: PersistentCollection {#7357 ▶}
          }
        ]
      }
      #initialized: true
    }
    -type: Type {#7541 ▶}
  }
  1 => Fields {#7542 ▼
    -id: 4
    -name: "horse"
    -unique_id: "bd7762b0e6"
    -productgroup: PersistentCollection {#7543 ▼
      -snapshot: []
      -owner: Fields {#7542}
      -association: array:20 [ …20]
      -em: EntityManager {#2815 …11}
      -backRefFieldName: "fields"
      -typeClass: ClassMetadata {#6494 …}
      -isDirty: false
      #collection: ArrayCollection {#7544 ▼
        -elements: []
      }
      #initialized: false
    }
    -type: Type {#7545 ▶}
  }
]

Now I connect horse also with the productgroup Animals. So my table fields_productgroup looks like this:

My fields_array for horse shows, that there is an element in the ArrayCollection but it does not contain the information for Animals. It is just an empty array... But I actually need the information to which productgroup horse is connected

array:2 [▼
  0 => Fields {#7460 ▼
    -id: 3
    -name: "cat"
    -unique_id: "5a38c820ed"
    -productgroup: PersistentCollection {#7464 ▼
      -snapshot: array:1 [ …1]
      -owner: Fields {#7460}
      -association: array:20 [ …20]
      -em: EntityManager {#2815 …11}
      -backRefFieldName: "fields"
      -typeClass: ClassMetadata {#6494 …}
      -isDirty: false
      #collection: ArrayCollection {#7465 ▼
        -elements: array:1 [▼
          0 => Productgroup {#7146 ▼
            -id: 6
            -name: "Animals"
            -unique_id: "9e4ef1c46f"
            -fields: PersistentCollection {#7357 ▶}
          }
        ]
      }
      #initialized: true
    }
    -type: Type {#7541 ▶}
  }
  1 => Fields {#7542 ▼
    -id: 4
    -name: "horse"
    -unique_id: "bd7762b0e6"
    -productgroup: PersistentCollection {#7543 ▼
      -snapshot: array:1 [ …1]
      -owner: Fields {#7542}
      -association: array:20 [ …20]
      -em: EntityManager {#2815 …11}
      -backRefFieldName: "fields"
      -typeClass: ClassMetadata {#6494 …}
      -isDirty: false
      #collection: ArrayCollection {#7544 ▼
        -elements: array:1 [▼
          0 => Productgroup {#7146}
        ]
      }
      #initialized: true
    }
    -type: Type {#7545 ▶}
  }
]

My fields entity:

  /**
  * @ORM\ManyToMany(targetEntity="Productgroup", inversedBy="fields")
  * @ORM\JoinColumn(name="productgroup", referencedColumnName="id")
  */
  private $productgroup;


public function getProductgroup()
  {
    return $this->productgroup;
  }

  public function setProductgroup($productgroup): self
  {
    $this->productgroup = $productgroup;

    return $this;
  }

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

Answer 1

First of all I think you are confusing the PHP Objects with PHP Arrays. But judging from your screenshots it seems that you have exactly what you wanted, the "horse" object has its productgroup association fully loaded.

This can be observed in your dumps:

As one can see the related Productgroup object's uid is #7146 for both the cat and the horse object, as expected since they are related the same product group.

I think that you just have been misled by the fact that horse's Productgroup is not expandable in your dump.