Nextras\Orm\Model\MetadataStorage::get PHP Method

    public static function get($className)
    {
        if (!isset(static::$metadata[$className])) {
            if (static::$metadata === null) {
                throw new InvalidStateException("MetadataStorage::get() called too early. You have to instantiate your model first.");
            }
            throw new InvalidArgumentException("Entity metadata for '{$className}' does not exist.");
        }
        return static::$metadata[$className];
    }

 private function parseCondition(array $levels, IMapper $mapper)
 {
     /** @var IDbStorageReflection $reflection */
     $reflection = $mapper->getStorageReflection();
     $expression = '';
     $column = array_pop($levels);
     $entityMD = $this->metadataStorage->get($mapper->getRepository()->getEntityClassNames()[0]);
     foreach ($levels as $level) {
         if (!$entityMD->hasProperty($level)) {
             throw new InvalidArgumentException("Undefined property {$entityMD->className}::\${$level}.");
         }
         $propertyMD = $entityMD->getProperty($level);
         if (!$propertyMD->relationshipRepository) {
             throw new InvalidArgumentException("Entity {$entityMD->className}::\${$level} does not contain a relationship.");
         }
         $targetMapper = $this->model->getRepository($propertyMD->relationshipRepository)->getMapper();
         $targetReflection = $targetMapper->getStorageReflection();
         if ($propertyMD->relationshipType === PropertyMetadata::RELATIONSHIP_ONE_HAS_MANY) {
             $table = $targetReflection->getStorageName();
             $joinColumn = $targetReflection->convertEntityToStorageKey($propertyMD->relationshipProperty);
             $expression .= ":{$table}({$joinColumn})";
         } elseif ($propertyMD->relationshipType === PropertyMetadata::RELATIONSHIP_MANY_HAS_MANY) {
             if ($propertyMD->relationshipIsMain) {
                 $expression .= ':' . $reflection->getManyHasManyStorageName($targetMapper);
                 $expression .= '.' . $reflection->getManyHasManyStoragePrimaryKeys($targetMapper)[1];
             } else {
                 $expression .= ':' . $targetReflection->getManyHasManyStorageName($mapper);
                 $expression .= '.' . $targetReflection->getManyHasManyStoragePrimaryKeys($mapper)[0];
             }
         } else {
             $expression .= '.' . $reflection->convertEntityToStorageKey($level);
         }
         $mapper = $targetMapper;
         $reflection = $targetReflection;
         $entityMD = $this->metadataStorage->get($mapper->getRepository()->getEntityClassNames()[0]);
     }
     // check if property exists
     $entityMD->getProperty($column);
     $column = $reflection->convertEntityToStorageKey($column);
     return "{$expression}.{$column}";
 }