[11.x] Add pending attributes to child models

[tontonsb]

Problem

Currently a relationship like this:

public function children(): HasMany
{
    return $this->hasMany(ChildModel::class);
}

Allows you to query $parent->children()->get() as well as create related models $parent->children()->create() that can be queried by the former $parent->children()->get().

Meanwhile a scoped relationship like this:

public function children(): HasMany
{
    return $this->hasMany(ChildModel::class)->where('active', true);
}

Allows you to query for active records $parent->children()->get(), but doing $parent->children()->create() will insert an inactive (with the default value of active to be precise) child and $parent->children()->get() will not return what you just inserted.

Solution

I propose adding "pending attributes" on relationships to allow specifying additional attributes that should be applied when creating new models. In theory this would allow setting any attributes on the newly created related models, but in particular this would allow solving the above issue like this:

public function children(): HasMany
{
    return $this->hasMany(ChildModel::class)
        ->where('active', true)
        ->withAttributes([
            'active' => true,
        ]);
}

And with such setup $parent->children()->create() will create an active ChildModel.

The pending attributes serve as defaults that can be overriden:

public function children(): HasMany
{
    
    return $this->hasMany(ChildModel::class)
        ->withAttributes(['a' => 'A'])
        ->withAttributes(['b' => 'B'])
        ->withAttributes(['a' => 'AA']); // overriding the attribute by another withAttributes()
}

$parent->children()->create(); // ['a' => 'AA', 'b' => 'B']

// overriding during creation
$parent->children()->create(['b' => 'BB']); // ['a' => 'AA', 'b' => 'BB']

[taylorotwell]

@tontonsb thanks for the PR. One potential inconsistency to surface... We have this method:

public function withPivotValue($column, $value = null);

It works very similar to this method you have proposed; however, it also sets a "where" clause on the pivot table in addition to putting the specified value on any newly created pivot models.

I'm wondering if this method you're proposing should also set where clauses for the given attributes as well to keep things consistent?

[tontonsb]

@taylorotwell that would make this even more convenient for my usecases. I was going to use it with a corresponding ->where() call.

Should I also change the method to support an equivalent API? I.e.

    /**
     * @param  string|\Illuminate\Contracts\Database\Query\Expression|array<string, string>  $column
     * @param  mixed  $value
     */
    public function withAttribute($column, $value = null);

I'm now wondering whether I should investigate if this can be done on the Builder itself. I don't need it at the moment, but being able to not only Post::hidden()->count(), but also Post::hidden()->create() seems kinda elegant.

[taylorotwell]

@tontonsb yeah a similar API might be nice, in addition to withAttributes (plural)?

[tontonsb]

@taylorotwell I added there where setting and changed the API. And added test cases for all of that.

By trying it out in an actual project, I noticed that relations created using ->one() do not inherit the pending attributes which felt like a bug. To solve this I made the pendingAttributes public and set its value on the new relationship in the one() method. I didn't use ->withAttributes() as it would double the wheres which are already inherited. Let me know if this solution is too naive.

[tontonsb]

See #53720 for a simpler implementation (without manual handling in one()), but it changes the Builder itself instead of only the has/morphs relationships.