Proposal to filter on generic cypher expression

[stevenvdr]

For a project I wanted to order my nodes based on the distance from a certain point. For realising this in neomodel I have created my own NodeSet and QueryBuilder to support this. Is this functionality that would be wanted in the neomodel package. If so I could create a Pull request for this.

Below is the snippet to support a new function order_by_cypher that allows to use any cypher expression to use in order_by. The NodeSet adds the cypher expression to self._order_by after which it is picked up by the QueryBuilder when doing build_order_by (if the property exists on the model it will use the previous behaviour, if not it will use the cypher literal).

class OrderByCypherNode(StructuredNode):
    """
    Class that overrules the used NodeSet, so the order_by_cypher can
    be used
    """

    @classproperty
    def nodes(cls):
        """
        Returns a NodeSet object representing all nodes of the classes label
        :return: NodeSet
        :rtype: NodeSet
        """
        return OrderByCypherNodeSet(cls)


class OrderByCypherQueryBuilder(QueryBuilder):
    """ Querybuilder with support for generic cypher order_by statements """

    def build_order_by(self, ident, source):
        if '?' in source._order_by:
            self._ast['with'] = '{}, rand() as r'.format(ident)
            self._ast['order_by'] = 'r'
        else:
            self._ast['order_by'] = ['{}.{}'.format(ident, p)
                                     if hasattr(source.source_class, p)
                                     else p.format(ident=ident)
                                     for p in source._order_by]


class OrderByCypherNodeSet(NodeSet):
    """ NodeSet with support for generic cypher order_by statements """

    query_cls = OrderByCypherQueryBuilder

    def order_by_cypher(self, cypher):
        if not hasattr(self, '_order_by'):
            self._order_by = []
        self._order_by.append(cypher)

        return self

[oikonomou]

@stevenvdr I have a similar situation where I want to fetch ordered objects by a given list of custom uuids.
There is a way when using plain cypher but, through neomodel, I see that custom QueryBuilder needs to be implemented.
Have you found any other way of doing such work in neomodel or is this the only way?

[stevenvdr]

I've found the snippet that I posted to be the easiest solution. There might be other ways, but I haven't checked as the snippet did what I needed (which was sort by distance to a certain point)

[oikonomou]

@stevenvdr thanks for the advice! I think I will start implementing an extended QueryBuilder, too.

[aanastasiou]

@stevenvdr , @oikonomou Any updates on this?

[mariusconjeaud]

@owinogradow Could this be interesting to extend what you did on the ordering in the extension ?