serialization-groups Skill

Serialization Groups

Prefer one resource class per representation over groups for new designs. Before reaching for groups, consider a DTO split: one class per output shape and per input shape, each with a flat, explicit set of properties (see api-resource). Reasons groups are a poor default:

• The public shape becomes implicit and scattered. To know what GET /books returns you must mentally union every #[Groups] tag across the class hierarchy and cross-reference each operation's normalizationContext. A dedicated BookOutput DTO states the shape in one place.
• They complicate the metadata. Per-operation contexts, per-property #[Context], and group inheritance interact in ways that are hard to predict and hard to test.
• They block streaming serialization. API Platform's JsonStreamer path needs one static shape per class; a class whose output varies by group can't be streamed and falls back to the slower object normalizer.

Use groups when: you're working in an existing codebase already built on them (stay consistent), or a DTO split is genuinely overkill (one tiny read/write asymmetry on an internal resource). Otherwise, split the class.

The two contexts

normalizationContext governs reading (entity → JSON). denormalizationContext governs writing (JSON → entity). A property is only serialized/deserialized if one of its #[Groups] is listed in the active context.

use ApiPlatform\Metadata\ApiResource;
use Symfony\Component\Serializer\Attribute\Groups;

#[ApiResource(
    normalizationContext: ['groups' => ['book:read']],
    denormalizationContext: ['groups' => ['book:write']],
)]
class Book
{
    #[Groups(['book:read'])]                 // appears in output, ignored on input
    public ?int $id = null;

    #[Groups(['book:read', 'book:write'])]   // read and write
    public string $title = '';

    #[Groups(['book:write'])]                // write-only, e.g. a password
    public ?string $secret = null;
}

A property with no group in the active context is invisible: a field present on the entity but absent from the response is almost always a missing read group.

Naming convention

Use resource:operation-style group names — book:read, book:write, book:item:read. This keeps groups namespaced per resource so a read group on one class never accidentally pulls properties on another. Pairing a broad book:read with a narrower book:item:read lets item operations expose more than collections (see next section).

Per-operation contexts

Override the resource-level context on a single operation. Common pattern: a lean collection, a richer item view.

use ApiPlatform\Metadata\ApiResource;
use ApiPlatform\Metadata\Get;
use ApiPlatform\Metadata\GetCollection;
use ApiPlatform\Metadata\Patch;

#[ApiResource(normalizationContext: ['groups' => ['book:read']])]
#[GetCollection]                                                  // book:read only
#[Get(normalizationContext: ['groups' => ['book:read', 'book:item:read']])]
#[Patch(denormalizationContext: ['groups' => ['book:write']])]
class Book
{
    #[Groups(['book:read'])]
    public string $title = '';

    #[Groups(['book:item:read'])]            // only on the single-item GET
    public ?string $description = null;
}

Controlling embedded relations

A relation is embedded as a full object when the related class has a property in a group shared with the parent's context; otherwise it serializes as an IRI/string. This is how you choose embed-vs-reference:

#[ApiResource(normalizationContext: ['groups' => ['book:read']])]
class Book
{
    #[Groups(['book:read'])]
    public ?Author $author = null;          // embedded only if Author has a 'book:read' property
}

class Author
{
    #[Groups(['book:read'])]
    public string $name = '';               // this property pulls Author inline
}

Drop the book:read group from Author::$name and author collapses back to an IRI. This implicit coupling is exactly the kind of thing a DTO split makes explicit.

Per-property context override with #[Context]

#[Context] overrides serializer options for one property without a new group — useful for date formats or switching the normalization group on a single relation (embed the same related type at two depths):

use Symfony\Component\Serializer\Attribute\Context;
use Symfony\Component\Serializer\Attribute\Groups;
use Symfony\Component\Serializer\Normalizer\DateTimeNormalizer;

class Book
{
    #[Groups(['book:read'])]
    #[Context([DateTimeNormalizer::FORMAT_KEY => 'Y-m-d'])]
    public ?\DateTimeInterface $publishedAt = null;

    #[Groups(['book:read'])]
    #[Context(['normalization' => ['groups' => ['author:summary']]])]
    public ?Author $author = null;          // serialized with author:summary, not book:read
}

The normalization/denormalization keys scope the override to one direction. See the parallel example in state-provider (Per-Property Serialization Context).

Interaction with other features

• Validation groups are separate from serialization groups — don't reuse the same names expecting them to align. See operations for validationContext.
• security expressions on properties (security: "is_granted(...)") gate fields independently of groups; both must pass.

Laravel (Eloquent)

API Platform uses the Symfony Serializer on Laravel too, so normalizationContext / denormalizationContext, the two-context model, per-operation contexts and embed-vs-IRI behaviour are identical. The one difference: Eloquent models have no typed properties, so #[Groups] can't be attached per property. Declare groups at the class level via #[ApiProperty(serialize: …, property: …)]:

use ApiPlatform\Metadata\ApiProperty;
use ApiPlatform\Metadata\ApiResource;
use Symfony\Component\Serializer\Attribute\Groups;

#[ApiResource(normalizationContext: ['groups' => ['book:read']])]
#[ApiProperty(serialize: new Groups(['book:read']), property: 'title')]
#[ApiProperty(serialize: new Groups(['book:read']), property: 'author')]
class Book extends Model {}

DTO/ApiResource classes (not extending Model) use property-level #[Groups] as shown above. The name_converter (default SnakeCaseToCamelCaseNameConverter) is set in config/api-platform.php.

Checklist

• Considered a DTO-per-shape split before adding groups (see api-resource)
• Group names namespaced per resource (book:read, not bare read)
• Write-only secrets carry only the write group
• Embedded-vs-IRI relations verified against actual JSON, not assumed
• #[Context] used for one-off format/group tweaks instead of a whole new group