Illuminate\Database\Eloquent\Builder::withCount PHP Method

    public function withCount($relations)
    {
        if (is_null($this->query->columns)) {
            $this->query->select(['*']);
        }
        $relations = is_array($relations) ? $relations : func_get_args();
        foreach ($this->parseWithRelations($relations) as $name => $constraints) {
            // First we will determine if the name has been aliased using an "as" clause on the name
            // and if it has we will extract the actual relationship name and the desired name of
            // the resulting column. This allows multiple counts on the same relationship name.
            $segments = explode(' ', $name);
            if (count($segments) == 3 && Str::lower($segments[1]) == 'as') {
                list($name, $alias) = [$segments[0], $segments[2]];
            }
            $relation = $this->getHasRelationQuery($name);
            // Here we will get the relationship count query and prepare to add it to the main query
            // as a sub-select. First, we'll get the "has" query and use that to get the relation
            // count query. We will normalize the relation name then append _count as the name.
            $query = $relation->getRelationCountQuery($relation->getRelated()->newQuery(), $this);
            $query->callScope($constraints);
            $query->mergeModelDefinedRelationConstraints($relation->getQuery());
            // Finally we will add the proper result column alias to the query and run the subselect
            // statement against the query builder. Then we will return the builder instance back
            // to the developer for further constraint chaining that needs to take place on it.
            $column = snake_case(isset($alias) ? $alias : $name) . '_count';
            $this->selectSub($query->toBase(), $column);
        }
        return $this;
    }

 /**
  * Add subselect queries to count the relations.
  *
  * @param mixed $relations
  * @return $this 
  * @static 
  */
 public static function withCount($relations)
 {
     return \Illuminate\Database\Eloquent\Builder::withCount($relations);
 }