Case insensitive keys for relation models #22

 $dataProvider = new ActiveDataProvider([
            'query' => $query->joinWith(['someCaseInsensitiveRelation']),
        ]);

//vendor/yiisoft/yii2/db/ActiveRelationTrait.php

    private function normalizeModelKey($value)
    {
        if (is_object($value) && method_exists($value, '__toString')) {
            // ensure matching to special objects, which are convertable to string, for cross-DBMS relations, for example: `|MongoId`
            $value = $value->__toString();
        }

        return $this->useCaseInsensitiveKeys ? strtolower($value) : $value;
    }