[5.4] Macroable relations

[thecrypticace]

Does what it says on the tin. Makes relations Macroable so one could, say, add a toHasOne method to HasMany without subclassing it.

h/t to @adamwathan for getting the gears turning on this idea.

[sileence]

Hello @thecrypticace. I read the post about this feature here: https://laravel-news.com/relationship-macros

But I'm wondering if something like:

public function logins()
{
    return $this->hasMany(Login::class);
}

public function lastLogin()
{
    return $this->hasOne(Login::class)->latest();
}

Does not achieve the same? I'd like to understand this better because I'd like to talk about it, so I'd appreciate if you send me or post other links or examples about this feature.

[thecrypticace]

The code snippet you have does indeed achieve the same thing. However, the example of a toHasOne macro is useful when you have an existing relationship with additional constraints on it (where clauses, orders, etc…) especially if any of them happen to be non-trivial. Really it's an application of DRY as you don't need to repeat them on a different relationship.

In a simple case like the above I would still prefer the use of $this->hasOne. The example was really meant show what one particular thing you can do should you want / need to.

[sileence]

thank you, @thecrypticace. I was just curious about other examples / use cases.

[BartHuis]

@thecrypticace hi, also saw the post in the LN newsletter. Do you have an example of the "However, the example of a toHasOne macro is useful when you have an existing relationship with additional constraints on it (where clauses, orders, etc…) especially if any of them happen to be non-trivial." case so we can understand when this should be usefull?
Bart

[DesmondPang]

I would like to create MorphToMany to toHasOne but it does not work.

MorphToMany::macro('toHasOne', function() {
            return new HasOne(
                $this->query,
                $this->parent,
                $this->foreignKey,
                $this->localKey
            );
        });

[mattkoch614]

I'd like to be able to do this for a BelongsToMany relationship if possible.

Something like:

        BelongsToMany::macro('toHasOne', function() {
            return new HasOne(
                $this->query,
                $this->parent,
                $this->foreignKey,
                $this->relatedKey
            );
        });

[thecrypticace]

Afaik there'd be no way to convert a many-to-many relationship into a one-to-one relationship. One side has to be constrained by a single model.