json_encode Recursion Detected

Why This Happens

json_encode() cannot handle objects or arrays that reference themselves, creating an infinite loop. This happens with parent-child relationships where a child references its parent, Doctrine entities with bidirectional associations, or tree structures with back-references.

The Problem

class Category {
    public string $name;
    public ?Category $parent = null;
    public array $children = [];
}
$parent = new Category();
$parent->name = 'Root';
$child = new Category();
$child->name = 'Sub';
$child->parent = $parent; // Circular!
$parent->children[] = $child;
echo json_encode($parent); // Recursion detected

The Fix

class Category implements JsonSerializable {
    public string $name;
    public ?Category $parent = null;
    public array $children = [];

    public function jsonSerialize(): mixed {
        return [
            'name' => $this->name,
            'children' => $this->children, // Don't include parent
        ];
    }
}

Step-by-Step Fix

1. 1

   Find the circular reference

   Identify which objects reference each other in a cycle. Look for parent-child, bidirectional, or self-referencing relationships.

2. 2

   Implement JsonSerializable

   Have the class implement JsonSerializable and define jsonSerialize() to return only the properties needed, excluding back-references.

3. 3

   Use a serialization library

   For complex object graphs, use a serialization library like Symfony Serializer that supports circular reference handling.