Multi-edges between two nodes

[spranger]

Hello, I use the new version 0.5.1 of grand-graph:

from grand import Graph
from grandcypher import GrandCypher
from grand.backends._sqlbackend import SQLBackend

backend=SQLBackend(db_url="sqlite:///demo2.db")
G = Graph(backend=backend)

G.nx.add_node("spranger", type="Person")
G.nx.add_node("meier", type="Person")
G.nx.add_node("krause", type="Person")
G.nx.add_node("Berlin", type="City")
G.nx.add_node("Paris", type="City")
G.nx.add_node("London", type="City")

G.nx.add_edge("spranger", "Paris", type="LIVES_IN")
G.nx.add_edge("krause", "Berlin", type="LIVES_IN")
G.nx.add_edge("meier", "London", type="LIVES_IN")
G.nx.add_edge("spranger", "Berlin", type="BORN_IN")
G.nx.add_edge("krause", "Berlin", type="BORN_IN")
G.nx.add_edge("meier", "Berlin", type="BORN_IN")


result1 = GrandCypher(G.nx).run("""
MATCH (n)-[r]->(c)
WHERE
    n.type == "Person"
    and
    c.type == "City"
    
RETURN n, r, c    
""")

from lark.lexer import Token
n = result1[Token('CNAME', 'n')]
r = result1[Token('CNAME', 'r')]
c = result1[Token('CNAME', 'c')]

for i in range(len(n)):
    print(f"{n[i]} - {r[i].get('type')} -> {c[i]}")

backend.commit()
backend.close()

results in

• spranger - BORN_IN -> Berlin
• spranger - LIVES_IN -> Paris
• meier - BORN_IN -> Berlin
• meier - LIVES_IN -> London
• krause - BORN_IN -> Berlin-

1. The "krause - LIVES_IN -> Berlin" relation is not stored (as any second relation between two same nodes) .
   This might be due to the cause that our "G.nx" doesn't cope with multigraphs.
2. In plain grandcypher I can query "Match (p:Person)" . How do I do this in my cypher query above?
3. Would it be a good idea to have the backend and the graph layer (e.g. netwrokx) completely transparent and just run Cypher queries, also for creating nodes and relations?

Kind Regards.
Steffen, the graphologist

[j6k4m8]

Hi @spranger! @jackboyla just added support for multigraphs in Grand-Cypher here: aplbrain/grand-cypher#42

So that's certainly going to help here. I also think (need to do a deeper dive before I can confirm) that this is indeed a limitation of Grand right now; I don't think we support MultiGraphs very well. (Maybe @acthecoder23 this would be a fun project to chew on?)

Just thinking out loud, probably the correct answer is to split Graph/DiGraph/MultiGraph/MultiDiGraph implementations like we briefly discuss in this issue: #44 ...

A short-term solution might be to create a MultiDiGraph in networkx itself (rather than in Grand) and try out @jackboyla's new implementation (which I'll have on PyPI / pip-installable shortly in grand-cypher==0.8.0). If that works for you, then we'll know the next step is support for multigraphs in the Grand backends!

[j6k4m8]

PS: Just got back from a week in Berlin, and totally thinking about adding a LIVES_IN edge there someday... :)

[acthecoder23]

@j6k4m8 I can give this a shot. I'll have to do a little digging but it'd be worthwhile

[jackboyla]

@spranger also to answer 2. -- to MATCH (a:friend) you need to assign the node label to the __labels__ attribute, in a set. We should probably include this in the README as it's not immediately obvious :) hopefully the multigraph support helps too:

from grandcypher import GrandCypher
import networkx as nx

host = nx.MultiDiGraph()
host.add_node("a", name="Alice", age=30)
host.add_node("b", name="Bob", age=40)
host.add_node("c", name="Charlie", age=50)
host.add_edge("a", "b", __labels__={"friend"}, years=3)  # <---
host.add_edge("a", "c", __labels__={"colleague"}, years=10)
host.add_edge("a", "c", __labels__={"parent"}, duration='forever')
host.add_edge("b", "c", __labels__={"colleague"}, duration=10)
host.add_edge("b", "c", __labels__={"mentor"}, years=2)

qry = """
MATCH (a)-[r]->(b)
RETURN a.name, b.name, r.__labels__, r.duration
"""
res = GrandCypher(host).run(qry)
print(res)

'''
{'a.name': ['Alice', 'Alice', 'Bob'], 
'b.name': ['Bob', 'Charlie', 'Charlie'], 
'r.__labels__': [{0: {'friend'}}, {0: {'colleague'}, 1: {'parent'}}, {0: {'colleague'}, 1: {'mentor'}}], 
'r.duration': [{0: None}, {0: None, 1: 'forever'}, {0: 10, 1: None}]}
'''