What is the correctly way to delete edges with orientdb OGM in django rest framework?

Question

I don't know how to create a method to delete edges in django rest framework, using orientdb OGM.

I'm using pyorient==1.5.5 and OrientDB 3.0.18 version.

I have two vertex Classes: ousers, ocompany. Also I have two relationships (edges) Classes: ofriends, oworksat. So for example:

To make a ofriends relationship, I need two ousers. And to make a oworksat relationship, I need one ouser and one ocompany. Every relationship has it own cluster id.

I know that I can access to these functions:

(Pdb) dir(graph)

['PROPERTY_TYPES', '_GROOVY_GET_DB', '_GROOVY_NULL_LISTENER', '_GROOVY_TRY', 'class', 'delattr', 'dict', 'dir', 'doc', 'eq', 'format', 'ge', 'getattribute', 'gt', 'hash', 'init', 'le', 'lt', 'module', 'ne', 'new', 'reduce', 'reduce_ex', 'repr', 'setattr', 'sizeof', 'str', 'subclasshook', 'weakref', '_last_cred', '_last_db', '_last_user', 'batch', 'both', 'bothE', 'build_mapping', 'clear_registry', 'client', 'coerce_class_names', 'coerce_class_names_to_quoted', 'compute_all_properties', 'config', 'create_all', 'create_class', 'create_edge', 'create_edge_command', 'create_function', 'create_props_mapping', 'create_vertex', 'create_vertex_command', 'delete_vertex', 'delete_vertex_command', 'drop', 'drop_all', 'drop_class', 'edge_from_record', 'edges_from_records', 'element_from_link', 'element_from_record', 'elements_from_links', 'elements_from_records', 'export', 'get_edge', 'get_element', 'get_vertex', 'gremlin', 'guard_reserved_words', 'inE', 'in_', 'include', 'init_broker_for_class', 'list_superclasses', 'ocompany', 'ofriends', 'open', 'ousers', 'out', 'outE', 'oworksat', 'populate', 'property_from_schema', 'props_from_db', 'props_to_db', 'query', 'registry', 'save_element', 'scripts', 'server_version', 'strict', 'toposort_classes', 'valid_element_base', 'vertex_from_record', 'vertexes_from_records']

If I do:

graph.delete_vertex("#21:0")

It works good and deletes #21:0 ouser vertex row, which is part of ofriends and oworskat relationships, so also, that command deletes the relationship where that vertex is included. Obviously, I don't want to delete the entire vertex, just only the specific edge (not the class, just the relationship row).

I was wondering if exists some command like delete_edge(), but dir(graph) don't tell me nothing related.

settings.py

from pyorient.ogm import Graph, Config
from pyorient.serializations import OrientSerialization
from pyorient.ogm import declarative

BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))

config = RawConfigParser()
config.read(BASE_DIR + '/settings.ini')

ORIENTDB = {
    'NAME': config.get('orientdbConf', 'DB_NAME'),
    'USER': config.get('orientdbConf', 'DB_USER'),
    'PASSWORD': config.get('orientdbConf', 'DB_PASS'),
    'HOST': config.get('orientdbConf', 'DB_HOST'),
    'PORT': config.get('orientdbConf', 'DB_PORT'),
}

Config.from_url('plocal://'+ORIENTDB['HOST']+':'+str(ORIENTDB['PORT'])+'/'+ORIENTDB['NAME']+'',''+ORIENTDB['USER']+'', ''+ORIENTDB['PASSWORD']+'',initial_drop=False,serialization_type=OrientSerialization.Binary)
graph = Graph(Config.from_url(''+ORIENTDB['HOST']+'/'+ORIENTDB['NAME']+'',''+ORIENTDB['USER']+'', ''+ORIENTDB['PASSWORD']+'',initial_drop=False))
Node = declarative.declarative_node()
Relationship = declarative.declarative_relationship()

models.py

from core.settings import Node,Relationship,graph
from pyorient.ogm.property import (String, Date, DateTime, Decimal, Double,
    Integer, Boolean, EmbeddedMap, EmbeddedSet,Link, UUID)

class OUsers(Node):
    element_plural = 'ousers'
    postgresql_id=Integer(nullable=False,unique=True)

class OCompany(Node):
    element_plural = 'ocompany'
    postgresql_id=Integer(nullable=False,unique=True)

class OFriends(Relationship):
    label = 'ofriends'
    from_postgresql_ouser_id=Integer(nullable=False,unique=True)
    to_postgresql_ouser_id=Integer(nullable=False,unique=True)

class OWorksAt(Relationship):
    label = 'oworksat'
    from_postgresql_ouser_id=Integer(nullable=False,unique=True)
    to_postgresql_ocompany_id=Integer(nullable=False,unique=True)

graph.create_all(Node.registry)
graph.create_all(Relationship.registry)

serializers.py

from .models import (OUsers,OCompany,OFriends,OWorksAt)
from rest_framework import serializers
from django.contrib.auth import get_user_model
User = get_user_model()

class OFriendsSerializer(serializers.Serializer):
    from_postgresql_ouser_id = serializers.IntegerField()
    to_postgresql_ouser_id = serializers.IntegerField()

    def create(self, data):
        return OFriends.objects.create(**data)

    def update(self, instance, data):
        instance.from_postgresql_ouser_id = data.get("from_postgresql_ouser_id")
        instance.to_postgresql_ouser_id = data.get("to_postgresql_ouser_id")
        instance.save()
        return instance

class OFriendsSerializer(serializers.Serializer):
    from_postgresql_ouser_id = serializers.IntegerField()
    to_postgresql_ouser_id = serializers.IntegerField()

    def create(self, data):
        return OFriends.objects.create(**data)

    def update(self, instance, data):
        instance.from_postgresql_ouser_id = data.get("from_postgresql_ouser_id")
        instance.to_postgresql_ouser_id = data.get("to_postgresql_ouser_id")
        instance.save()
        return instance

api.py

class OFriendsViewSet(viewsets.ModelViewSet):

    def destroy(self, request, *args, **kwargs):
        queryset = graph.ofriends.query()
        import pdb;pdb.set_trace()
        # HERE should be the command 

Answer 1

According with the pyorient OGM documentation, that functionality was never added. I already created an issue in the repository.

So at the moment, I solved my problem using pyorient client, with raw query:

pyorient_client.py

from core.settings import ORIENTDB
import pyorient

def orientdbConnection():
    """Orientdb client connection"""
    client = None
    try:
        client = pyorient.OrientDB(ORIENTDB['HOST'], int(ORIENTDB['PORT']))
        session_id = client.connect( ORIENTDB['USER'], ORIENTDB['PASSWORD'] )
        if client.db_exists( ORIENTDB['NAME'], pyorient.STORAGE_TYPE_MEMORY ):
            client.db_open( ORIENTDB['NAME'], ORIENTDB['USER'], ORIENTDB['PASSWORD'])
    except Exception as e:
        print ("[ ERROR ] Fail orientdb connection. Error: " + str(e))
    return client

And in the api.py

from rest_framework import status
from rest_framework.response import Response
from core.pyorient_client import *

class OFriendsViewSet(viewsets.ModelViewSet):

    def destroy(self, request, *args, **kwargs):
        client = orientdbConnection()

        client.command("delete edge ofriends where @rid = '" + kwargs['pk'] + "'")

        return Response(status=status.HTTP_204_NO_CONTENT)

Maybe this could be useful for anyone else. Note that I receive o'friends @rid as a parameter (by passing the id in DELETE method in swagger UI).

Answer 2

An alternative to constructing the command yourself is to use Graph.record_delete() and passing it the record ID of the edge to delete.

The code snippet below assume that db is an instance of OrientDB and rid holds the record ID of the link to delete:

cluster = rid[1:].split(':')[0]
record = rid[1:].split(':')[1]
db.record_delete(cluster, record)

As a sidebar, the more I work with OrientDB, the more I regret my choice of database given the lack of support for the Python driver which is functionally incomplete and now also very out of date.