yii\db\ActiveQuery::joinWithRelation PHP Method

    private function joinWithRelation($parent, $child, $joinType)
    {
        $via = $child->via;
        $child->via = null;
        if ($via instanceof ActiveQuery) {
            // via table
            $this->joinWithRelation($parent, $via, $joinType);
            $this->joinWithRelation($via, $child, $joinType);
            return;
        } elseif (is_array($via)) {
            // via relation
            $this->joinWithRelation($parent, $via[1], $joinType);
            $this->joinWithRelation($via[1], $child, $joinType);
            return;
        }
        list($parentTable, $parentAlias) = $this->getQueryTableName($parent);
        list($childTable, $childAlias) = $this->getQueryTableName($child);
        if (!empty($child->link)) {
            if (strpos($parentAlias, '{{') === false) {
                $parentAlias = '{{' . $parentAlias . '}}';
            }
            if (strpos($childAlias, '{{') === false) {
                $childAlias = '{{' . $childAlias . '}}';
            }
            $on = [];
            foreach ($child->link as $childColumn => $parentColumn) {
                $on[] = "{$parentAlias}.[[{$parentColumn}]] = {$childAlias}.[[{$childColumn}]]";
            }
            $on = implode(' AND ', $on);
            if (!empty($child->on)) {
                $on = ['and', $on, $child->on];
            }
        } else {
            $on = $child->on;
        }
        $this->join($joinType, empty($child->from) ? $childTable : $child->from, $on);
        if (!empty($child->where)) {
            $this->andWhere($child->where);
        }
        if (!empty($child->having)) {
            $this->andHaving($child->having);
        }
        if (!empty($child->orderBy)) {
            $this->addOrderBy($child->orderBy);
        }
        if (!empty($child->groupBy)) {
            $this->addGroupBy($child->groupBy);
        }
        if (!empty($child->params)) {
            $this->addParams($child->params);
        }
        if (!empty($child->join)) {
            foreach ($child->join as $join) {
                $this->join[] = $join;
            }
        }
        if (!empty($child->union)) {
            foreach ($child->union as $union) {
                $this->union[] = $union;
            }
        }
    }