Laravel eloquent get relation count

Define a articles() relation in your Category model as:

public function articles() 
{
    return $this->hasMany(Article::class, 'cat_id');
}

Then you can try it as:

Category::where('parent_id', 0)->withCount('articles')->get();

You can use the hasManyThrough() Eloquent method to fetch all of the childrens' Articles, then add the article counts together in a nice little getter. I added the getter to the $appends array on the model to help illustrate it in the Tinker output.

class Category extends Model
{

    protected $appends = [
        'articleCount'
    ];

    public function articles()
    {
        return $this->hasMany(Article::class);
    }

    public function children()
    {
        return $this->hasMany(Category::class, 'parent_id');
    }

    public function childrenArticles()
    {
        return $this->hasManyThrough(Article::class, Category::class, 'parent_id');
    }

    public function getArticleCountAttribute()
    {
        return $this->articles()->count() + $this->childrenArticles()->count();
    }
}

Here's the Tinker output:

Psy Shell v0.8.0 (PHP 7.0.6 — cli) by Justin Hileman
>>> $cat = App\Category::first();
=> App\Category {#677
     id: "1",
     name: "Cooking",
     parent_id: null,
     created_at: "2016-12-15 18:31:57",
     updated_at: "2016-12-15 18:31:57",
   }
>>> $cat->toArray();
=> [
     "id" => 1,
     "name" => "Cooking",
     "parent_id" => null,
     "created_at" => "2016-12-15 18:31:57",
     "updated_at" => "2016-12-15 18:31:57",
     "articleCount" => 79,
   ]
>>> 

If you want to restrict your Category query to ones that have children that have articles, you could do that using the has() method:

Category::has('children.articles')->get();

Here's more on the has() method:

https://laravel.com/docs/5.3/eloquent-relationships#querying-relationship-existence

And the hasManyThrough() method:

https://laravel.com/docs/5.3/eloquent-relationships#has-many-through

  public function NoOfStudent()
    {
        return $this->hasMany(UserAssignment::class,'assignment_id','id');
    }



$assignment = Assignment::select('id','batch_id','title','description','attachment','last_submission_date',DB::raw('(CASE WHEN type = 9 THEN "Quiz Type"  ELSE "Descriptive" END) AS assignment_type'),DB::raw('(CASE WHEN status = 1 THEN "Assigned"  ELSE "Not Assigned" END) AS status'))
                      ->with('assignmentBatch:id,batch_number')
                      ->where('assignments.instructor_id',auth('api')->user()->id)
                      ->orderBy('created_at','DESC');
        if(!$request->user_id){
            $assignment =$assignment->withCount('NoOfStudent');
        }

In regards to Carlos_E.'s answer:

You can improve the query by using whereHas instead of whereIn:

$agents = Agents::whereHas('schedule')
  ->with('schedules')
  ->get();

This should work:

$category
->where('categories.parent_id', 0)
->leftJoin('article', 'article.cat_id', '=', 'categories.id')
->select('categories.id', \DB::raw('COUNT(article.id)'))
->groupBy('categories.id')
->get();

The above query will get you category IDs and count of all articles that belong to the category.

After reading your question and comments again, if I understand correctly you want to get the count of all articles that belong to those categories (with parent_id = 0) + the count of articles that belong to sub categories (those with parent_id = (id of some category)).

Now I have no way of testing this easily, but I think something along these lines should work for that.

$category
->where('categories.parent_id', 0)
->leftJoin('article', 'article.cat_id', '=', 'categories.id')
->leftJoin('categories as c2', 'c2.parent_id', '=', 'categories.id')
->leftJoin('article as a2', 'a2.cat_id', '=', 'c2.id')
->select('categories.id', \DB::raw('(COUNT(article.id)) + (COUNT(a2.id)) as count'))
->groupBy('categories.id')
->get();

That beign said, I think you're better of having a column named count in categories and update it each time a new article gets added. For performance.

I am sure somebody is still going through this, I was able to solve it the following way, suppose I have an Agent model and a Schedule model, i.e. one agent may have many schedules:

class Schedule extends Model {
  public function agent() {
    return $this->belongsTo(Agent::class, 'agent_id');
  }
}

class Agent extends Model {
  public function user(){
    return $this->belongsTo(User::class);
  }

  public function schedules(){
    return $this->hasMany(Schedule::class);
  }
}

Well some agents may not necessarily have schedules assigned, thus, I filtered those before calling the with() method, like this:

$agents = Agents::whereIn(
    'id', 
    Schedule::distinct()->pluck('agent_id')
)->with('schedules')->get();

Hope this helps!.