ORM: setting information from the reverse side, removing orphans.

src/Controller/ProductController.php

@@ -152,9 +152,14 @@ SQL;
 
     $category = $product->getCategory();
 
+    /* How to remove a product using automatic orphans removal
+    $category->removeProduct($product);
+    $this->getDoctrine()->getManager()->flush();
+    */
+
     return $this->render('product/product.html.twig', [
       'product' => $product,
-      'category' => $category->getName(),
+      'category' => $category ? $category->getName() : '?',
     ]);
   }
 

src/Entity/Category.php

@@ -29,7 +29,8 @@ class Category
    *
    * @ORM\OneToMany(
    *   targetEntity = "App\Entity\Product",
-   *   mappedBy = "category"
+   *   mappedBy = "category",
+   *   orphanRemoval= true,
    * )
    */
   private $products;
@@ -38,6 +39,18 @@ class Category
     $this->products = new ArrayCollection();
   }
 
+  public function addProduct(Product $product): self {
+    // Avoid adding product twice.
+    if ($this->products->contains($product)) {
+      return $this;
+    }
+
+    $this->products[] = $product;
+    // Actually set the information on the *owning* side.
+    $product->setCategory($this);
+    return $this;
+  }
+
   /**
    * @return mixed
    */
@@ -59,6 +72,13 @@ class Category
     return $this->products;
   }
 
+  public function removeProduct(Product $product): self {
+    $this->products->removeElement($product);
+    // Set the *owning* side to null.
+    $product->setCategory(null);
+    return $this;
+  }
+
   /**
    * @param mixed $name
    *

src/Entity/Product.php

@@ -33,7 +33,7 @@ class Product
   /**
    * @ORM\Column(type="text"))
    */
-  private $description;
+  private $description = '';
 
   /**
    * @ORM\Id
@@ -55,7 +55,7 @@ class Product
   /**
    * @return \App\Entity\Category
    */
-  public function getCategory(): Category {
+  public function getCategory(): ?Category {
     return $this->category;
   }
 
@@ -67,9 +67,9 @@ class Product
   }
 
   /**
-   * @return int
+   * @return int|null
    */
-  public function getId(): int {
+  public function getId(): ?int {
     return $this->id;
   }
 
@@ -92,7 +92,7 @@ class Product
    *
    * @return \App\Entity\Product
    */
-  public function setCategory(Category $category): self {
+  public function setCategory(?Category $category = null): self {
     $this->category = $category;
     return $this;
   }