How to add where condition to eloquent model on relation?

Question

I want to add where condition to my Model when with('category') is called. My relations are like this:

class Post extends Model
{
    public function category()
    {
        return $this->belongsTo(Category::class);
    }
}

Now I use this code to display post categories:

Post::where('slug', $slug)->with('category')->get();

I want to add where condition to Post Model when with('category') is called. I should display only posts.status== published if with('category') is called.

I think return $this->belongsTo(Category::class); is where i should add my where condition, but this doesn't work:

return $this->query()->where('posts.status', 'published')->getModel()->belongsTo(User::class)

How can I add where condition to all post queries if with('category') is called? I know Laravel query scopes, but i think there is a simpler way we can use. (perhaps on $this->belongsTo(Category::class))

Answer 1

Relationships are implemented using additional queries. They are not part of the base query, and do not have access to modify the base query, so you cannot do this inside the relationship method.

The best way to do this is with a query scope:

Class:

class Post extends Model
{
    public function scopeWithCategory($query)
    {
        return $query->with('category')->where('status', 'published');
    }
}

Query:

$posts = Post::where('slug', $slug)->withCategory()->get();

Edit

Based on your comment, I think you've probably asked the wrong question. You may want to post another question explaining what you have setup, and what you need to do, and see if anyone has any suggestions from there.

However, to answer this specific question, I believe you should be able to do this using a global query scope. This is different than a local scope described in my original answer above.

Global query scopes are applied when get() is called on the Eloquent query builder. They have access to the query builder object, and can see the items that have been requested to be eager loaded. Due to this, you should be able to create a global query scope that checks if category is to be eager loaded, and if so, add in the status constraint.

class Post extends Model
{

    /**
     * The "booting" method of the model.
     *
     * @return void
     */
    protected static function boot()
    {
        // make sure to call the parent method
        parent::boot();

        static::addGlobalScope('checkCategory', function(\Illuminate\Database\Eloquent\Builder $builder) {
            // get the relationships that are to be eager loaded
            $eagers = $builder->getEagerLoads();

            // check if the "category" relationship is to be eager loaded.
            // if so, add in the "status" constraint.
            if (array_key_exists('category', $eagers)) {
                $builder->where('status', 'published');
            }
        });
    }
}

The code above shows adding in a global scope using an anonymous function. This was done for ease and clarity. I would suggest creating the actual scope class, as described in the documentation linked above.

Answer 2

This should work:

Post::where(['slug' => $slug, 'status' => 'published'])->with('category')->get();