LeanMapper\Entity::addToOrRemoveFrom PHP Method

    private function addToOrRemoveFrom($action, $name, $arg)
    {
        if ($this->isDetached()) {
            throw new InvalidMethodCallException('Cannot add or remove related entity to detached entity.');
        }
        if ($arg === null) {
            throw new InvalidArgumentException('Invalid argument given in entity ' . get_called_class() . '.');
        }
        if (is_array($arg) or $arg instanceof Traversable and !$arg instanceof Entity) {
            foreach ($arg as $value) {
                $this->addToOrRemoveFrom($action, $name, $value);
            }
        } else {
            $method = $action === self::ACTION_ADD ? 'addTo' : 'removeFrom';
            $property = $this->getCurrentReflection()->getEntityProperty($name);
            if ($property === null or !$property->hasRelationship() or !$property->getRelationship() instanceof Relationship\HasMany) {
                throw new InvalidMethodCallException("Cannot call {$method} method with '{$name}' property in entity " . get_called_class() . '. Only properties with m:hasMany relationship can be managed this way.');
            }
            if ($property->getFilters()) {
                throw new InvalidMethodCallException("Cannot call {$method} method with '{$name}' property in entity " . get_called_class() . '. Only properties without filters can be managed this way.');
                // deliberate restriction
            }
            $relationship = $property->getRelationship();
            if ($arg instanceof Entity) {
                if ($arg->isDetached()) {
                    throw new InvalidArgumentException('Cannot add or remove detached entity ' . get_class($arg) . " to {$name} in entity " . get_called_class() . '.');
                }
                $type = $property->getType();
                if (!$arg instanceof $type) {
                    $type = gettype($arg) !== 'object' ? gettype($arg) : 'instance of ' . get_class($arg);
                    throw new InvalidValueException("Unexpected value type given in property '{$property->getName()}' in entity " . get_called_class() . ", {$property->getType()} expected, {$type} given.");
                }
                $data = $arg->getRowData();
                $arg = $data[$this->mapper->getPrimaryKey($relationship->getTargetTable())];
            }
            $table = $this->mapper->getTable($this->getCurrentReflection()->getName());
            $values = [$relationship->getColumnReferencingSourceTable() => $this->row->{$this->mapper->getPrimaryKey($table)}, $relationship->getColumnReferencingTargetTable() => $arg];
            $method .= 'Referencing';
            $this->row->{$method}($values, $relationship->getRelationshipTable(), $relationship->getColumnReferencingSourceTable(), null, $relationship->getStrategy());
        }
    }