withAttached

WithAttachedMixin.php

/**
 *
 * Usage
 * 
 * Register in provider
 * Builder::mixin(new WithAttachedMixin);
 *
 * withAttached(
 *  relation name, 
 *  name of property (default = {relation_name}_{column}s),  
 *  subquery callback (default = null), 
 *  column name (default = id)
 * )
 * 
    $u = App\User::withAttached(
        'groups',
        'group_list',
        function($q) {
            $q->where('id', '>', 15);
        },
        'id'
    )->find(7);
        
    $u->group_list; // = [16,22,25,29]
 */

use Illuminate\Database\Query\Expression;

class WithAttachedMixin
{
    public function withAttached() {
        return function(
            $relationName,
            $alias = null,
            $subQuery = null,
            $column = 'id'
        ) {
            if (is_null($this->query->columns)) {
                $this->query->select([$this->query->from.'.*']);
            }

            $relation = $this->getRelationWithoutConstraints($relationName);

            // prepare group concat statement
            $expression = "concat( '[', GROUP_CONCAT($column SEPARATOR ',' ),']')";

            $query = $relation->getRelationExistenceQuery(
                $relation->getRelated()->newQuery(), $this, new Expression($expression)
            )->setBindings([], 'select');

            if ($subQuery !== null) {
                $query->callScope($subQuery);
            }

            $query = $query->mergeConstraintsFrom($relation->getQuery())->toBase();
            if (count($query->columns) > 1) {
                $query->columns = [$query->columns[0]];
            }
            if ($alias === null) {
                $alias = $relationName."_".$column."s";
            }
            $this->model->mergeCasts([$alias => 'array']);
            $this->selectSub($query, $alias);

            return $this;
        };
    }


}