> APIs > API Platform 3 Part 1: Mythically Good RESTful APIs
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10.

Serialization Groups: Choosing Fields

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Right now, whether or not a field in our class is readable or writable in the API is entirely determined by whether or not that property is readable or writable in our class (basically, whether or not it has a getter or setter method). But what if you need a getter or setter... but don't want that field exposed in the API? For that, we have two options.

A DTO Class?

Option número uno: create a DTO class for the API resource. This is something we'll save for another day... in a future tutorial. But in a nutshell, it's where you create a dedicated class for your DragonTreasure API... and then move the ApiResource attribute onto that. The key thing is that you'll design the new class to look exactly like your API... because modeling your API will be its only job. It takes a little more work to set things up, but the advantage is that you then have a dedicated class for your API. Done!

Hello Serialization Groups

The second solution, and the one we're going to use, is serialization groups. Check it out. Over on the ApiResource attribute, add a new option called normalizationContext. If you recall, "normalization" is the process of going from an object to an array, like when you're making a GET request to read a treasure. The normalizationContext is basically options that are passed to the serializer during that process. And the one option that's most important is groups. Set that to one group called treasure:read:

142 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 16
#[ApiResource(
// ... lines 18 - 26
normalizationContext: [
'groups' => ['treasure:read'],
]
)]
class DragonTreasure
{
// ... lines 33 - 140
}

We'll talk about what this does in a minute. But you can see the pattern I'm using for the group: the name of the class (it could be dragon_treasure if we wanted) then :read... because normalization means that we're reading this class. You can name these groups however you want: this is my standard.

So... what does that do? Let's find out! Refresh the documentation... and, to make life easier, go to the URL: /api/dragon_treasures.jsonld. Whoops! It's just treasures.jsonld now. There we go. And... absolutely nothing is returned! Ok, we have the hydra fields, but this hydra:member contains the array of treasures. It is returning one treasure... but other than @id and @type... there are no actual fields!

How Serialization Groups Work

Here's the deal. As soon as we add a normalizationContext with a group, when our object is normalized, the serializer will only include properties that have this group on it. And since we haven't added any groups to our properties, it returns nothing.

How do we add groups? With another attribute! Above the $name property, say #[Groups], hit "tab" to add its use statement and then treasure:read. Repeat this above the $description field... because we want that to be readable... and then the $value field... and finally $coolFactor:

147 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 14
use Symfony\Component\Serializer\Annotation\Groups;
// ... lines 16 - 31
class DragonTreasure
{
// ... lines 34 - 39
#[Groups(['treasure:read'])]
private ?string $name = null;
// ... lines 42 - 43
#[Groups(['treasure:read'])]
private ?string $description = null;
// ... lines 46 - 50
#[Groups(['treasure:read'])]
private ?int $value = null;
// ... lines 53 - 54
#[Groups(['treasure:read'])]
private ?int $coolFactor = null;
// ... lines 57 - 145
}

Good start. Move over and refresh the endpoint. Now... got it! We see name, description, value, and coolFactor.

DenormalizationContext: Controlling Writable Groups

We now have control over which fields are readable... and we can do the same thing to choose which fields should be writeable in the API. That's called "de-normalization", and I bet you can guess what we're going to do. Copy normalizationContext, paste, change it to denormalizationContext... and use treasure:write:

150 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 17
#[ApiResource(
// ... lines 19 - 30
denormalizationContext: [
'groups' => ['treasure:write'],
]
)]
class DragonTreasure
{
// ... lines 37 - 148
}

Now head down to the $name property and add treasure:write. I'm going to skip $description (remember that we actually deleted our setDescription() method earlier on purpose)... but add this to $value... and $coolFactor:

150 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 34
class DragonTreasure
{
// ... lines 37 - 42
#[Groups(['treasure:read', 'treasure:write'])]
private ?string $name = null;
// ... lines 45 - 53
#[Groups(['treasure:read', 'treasure:write'])]
private ?int $value = null;
// ... lines 56 - 57
#[Groups(['treasure:read', 'treasure:write'])]
private ?int $coolFactor = null;
// ... lines 60 - 148
}

Oh, it's mad at me! As soon as we pass multiple groups, we need to make this an array. Add some [] around those three properties. Much happier.

To check if this is A-OK, refresh the documentation... open up the PUT endpoint, and... sweet! We see name, value, and coolFactor, which are currently the only fields that are writable in our API.

Adding Groups To Methods

We are missing a few things, though. Earlier, we made a getPlunderedAtAgo() method...

150 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 34
class DragonTreasure
{
// ... lines 37 - 132
public function getPlunderedAtAgo(): string
{
return Carbon::instance($this->plunderedAt)->diffForHumans();
}
// ... lines 137 - 148
}

and we want this to be included when we read our resource. Right now, if we we check the endpoint, it's not there.

To fix this, we can also add groups above methods. Say #[Groups(['treasure:read'])]:

151 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 34
class DragonTreasure
{
// ... lines 37 - 132
#[Groups(['treasure:read'])]
public function getPlunderedAtAgo(): string
{
return Carbon::instance($this->plunderedAt)->diffForHumans();
}
// ... lines 138 - 149
}

And when we go check... voilà, it pops up.

Let's also find the setTextDescription() method... and do the same thing: #[Groups([treasure:write])]:

152 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 34
class DragonTreasure
{
// ... lines 37 - 93
#[Groups(['treasure:write'])]
public function setTextDescription(string $description): self
{
// ... lines 97 - 99
}
// ... lines 101 - 150
}

Awesome! If we head back to the documentation, the field is not currently there... but when we refresh... and check out the PUT endpoint again... textDescription is back!

Re-Adding Methods

Hey, now we can re-add any of the getter or setter methods we removed earlier! Like, maybe I do need a setDescription() method in my code for something. Copy setName() to be lazy, paste and change "name" to "description" in a few places.

Got it! And even though we have that setter back, when we look at the PUT endpoint, description doesn't show up. We have complete control over our fields thanks to the denormalization groups. Do the same thing for setPlunderedAt()... because sometimes it's handy - in data fixtures especially - to be able to set this manually.

And... done!

Adding Field Defaults

So we know that fetching a resource works. Now let's see if we can create a new resource. Click on the POST endpoint, hit "Try it out", and... let's fill in some info about our new treasure, which is, of course, a Giant jar of pickles. This is very valuable and has a coolFactor of 10. I'll also add a description... though this jar of pickles speaks for itself.

When we try this... oh, dear... we get a 500 error:

An exception occurred while executing a query: Not null violation, null value in column isPublished.

We slimmed our API down to only the fields that we want writeable... but there's still one property that must be set in the database. Scroll up and find isPublished. Yup, it currently defaults to null. Change that to = false... and now the property will never be null.

If we try it... the Giant jar of pickles is pickled into the database! It works!

Next: let's explore a few more cool serialization tricks to give us even more control.