[Eloquent Model] initialize traits after filling model to dynamically add attributes

[juliomotol]

Is there a way to where we could initialize traits for a model after filling its attributes?

framework/src/Illuminate/Database/Eloquent/Model.php

Lines 166 to 175 in 7395583

	public function __construct(array $attributes = [])
	{
	$this->bootIfNotBooted();
	$this->initializeTraits();
	$this->syncOriginal();
	$this->fill($attributes);
	}

The reasoning for this is I want my trait to initialize an attribute that depends on another column.

trait FooTrait
{
    protected function initializeFooTrait()
    {
        $this->attribute['dynamicly_loaded_mutator'] = 'some derived value from another attribute';
    }
}

During initializeFooTrait(), the model's attributes isn't filled yet, thus throwing errors.

Maybe add something like finalizeTraits() where you define finilizeFooTrait() in your trait.

I'd be very happy to make a PR for this <3

[austrowGC]

This seems like it could be handled using the 'retrieved' Model event, but I could be wrong. I'm looking into using it for a similar use case.

[juliomotol]

I've been skimming the Model class but the $attribute property is protected and it wont be mutable within the closure, unless you use $this->attribute but I'm very skeptical in doing that.

Maybe having a saving events that clears the added attributes from the retrieved. But it feels like running all around the places. 🤔

[austrowGC]

I'm confused about what you want to do, then. As far as I know, the protected $attributes member on a model is only supposed to represent the default values for fields. In the retrieved callback, you can directly set the value that you need to $model->attribute. The value of $model passed to that closure has data from the underlying table at that point and you can invoke whatever logic you need--I was just copying what you had used as a placeholder in your initial post.

[juliomotol]

Disregard what said about the saving event part, looking at the save() method of Model, it seems that this would work. I'll be doing my initial test later today.

[devfrey]

I've been skimming the Model class but the $attribute property is protected and it wont be mutable within the closure, unless you use $this->attribute but I'm very skeptical in doing that.

@juliomotol You can access $attributes within your closure just fine, since the closure is defined within the same class.

[yob-yob]

One Cons for this is that it's using the booted() method.. which would can cause a collision from other traits..

[UncertaintyP]

Because $this->attribute must be a property of your trait or you specific model (because Laravel does NOT have that property) you can set its visibility as you like and it must be available at startup. What is the error you are receiving?

[funder7]

Hi,
I'm probably facing the same issue as @juliomotol.

To give you a little more context:

• you have many Model classes using the trait
• the trait will modify the model, e.g. by adding an attribute
• you want to exclude the trait initialization on a specific condition, which depends on the value of another attribute

Right now you can't, as attributes are filled after trait(s) initialization.

This is very likely a corner case, but having the data available, would allow a more granular use of Traits.

Edit - a solution to this problem

1. Trait class

trait XYZTrait
{
    public bool $hasXYZTrait = true;  // will use this later to easily check if model uses the trait

    // ... trait content

    public function isExcludedType(): bool
    {
      
        if ($this instanceof YourModelToCheck) {
            return $this->propertyToCheck === 'valueThatExcludesTrait';
        }

        return $false;
    }

}

2. Example use

$modelHasXYZTrait = property_exists($model, 'hasXYZTrait');

$modelHasActiveTrait = $modelHasXYZTrait && $visitModel->isExcludedType() === false;

The property_exists() call is used to easily check if the model uses the trait. Correct me if I'm wrong, but php doesn't provide an easy solution to that.

[juliomotol]

Hi @funder7, I've forgotten what I was trying to solve and solution for this. But based on your case, you might be able to use models events as mentioned by @austrowGC

trait FooTrait
{
    public static function bootFooTrait()
    {
        self::retrieved(function (static $model) {
            if ($condition) {
                $model->dynamic_attribute = $value;
            }
        });
    }
}

If this attribute is derived from another and you want this to also be updated every time that has been updated, you may use a mutator.

protected function foo(): Attribute
{
    return Attribute::set(function ($value) {
        return with(
            ['foo' => $value], // You'll need to passthrough the dependency attribute so that It can also be saved.
            function ($items) {
                if ($condition) {
                    $items['dynamic_attribute'] => $someValue;
                }
            }
        );
    });
}

Note: Without the mutator, the attribute will never be filled when creating a new instance since it will only be loaded when retrieved.

Although from what I can remember about the origin of this discussion, I didn't want this attribute to be saved almost acting like an accessor. If that's also the case for you, you can use the saving event in the boot to unset() the added attribute

self::saving(function (static $model) {
    unset($model->dynamic_attribute);
});

Again I can't recall why I would go through the hassle of doing that (as you can see in some of my responses in the other comments), but a simpler approach would be to just use an accessor for this.

protected function dynamicAttribute(): Attribute
{
    return Attribute::get(function (){
        if $condition
            ? $value
            : null
    });
}