CODEWITHSUNDEEP
pythonneo4j
RMcG
RMcG

Reputation: 1095

Embedded Neo4j Python create or check for unique relationships

I'm using the neo4j python module neo4j-embedded to populate a neo4j graph. However I can't figure out how to make unique relationships between two nodes.

Currently I create a new relationship each time which is definitely not desired. The code below shows a simple example were I just create 9 nodes, and then look to connected them with the relationship "friendsWith", however currently these relationships are not unique and I end up with 153 relationships all but around 45 of which are redundant:

from neo4j import GraphDatabase
neo_db = GraphDatabase('../testdatabase/') 

with neo_db.transaction:                                                         
  person_idx = neo_db.node.indexes.create('people')   
  user_ids = [1,2,3,4,5,6,7,8,9]                                                 

  for user in user_ids:
    ##########################################################################
    ## Check if user exists in neo4j,                      
    ## If not create it and save id, otherwise find the id.                    
    ########################################################################## 
    person_node = person_idx['name'][user].single                              
    if person_node == None:                                                    
      person_node = neo_db.node(name=user)                                     
      person_idx['name'][user] = person_node                                   

    for friend in user_ids:                                                    
      ##########################################################################
      ## Check if friend exists in neo4j,                              
      ## If not create it and save id, otherwise find the id.                    
      ########################################################################## 
      friend_node = person_idx['name'][friend].single                          
      if friend_node == None:                                                  
        friend_node = neo_db.node(name=friend)                                 
        person_idx['name'][friend] = friend_node                               
      relationship = person_node.friendsWith(friend_node)

Is there any way of checking if a relationship of type "friendsWith" exists between two nodes using the python module mentioned above? Or a way of only creating the relationship if one of that type doesn't already exist.

I'm looking for a solution that preferable doesn't require querying the database using cypher and the query command.

Thanks for any help.

Edit:

I realise you can get the solution using cypher as follows, however I'm looking for a way that can be done using just python, ideally without any prior knowledge of cypher. Part of this being, I don't particularly want to have to write an ad-hoc query for functionality that I will be using extensively, just with different nodes and relationships. 

    result = neo_db.query("START n = node:people(name='%i'),m=node:people(name='%i') MATCH (n)-[r:friendsWith]-(m) RETURN r;"%(user,friend))
    if result.single == None:                                                   
      relationship = person_node.friendsWith(friend_node)

Upvotes: 1

Views: 429

Answers (1)

Michael Hunger
Michael Hunger

Reputation: 41706

Why don't you want to use cypher?

If you want to avoid duplicates, you have to:

  1. take a write lock (e.g. by removing some non-existant property from a "lock" node)
  2. find all current pairs / end-nodes and put them/their ids into a set structure
  3. when creating new relationships check against that set

Otherwise you have to iterate over all rels on each create to check if the current to be added target node is already connected to the current source node.

Upvotes: 1

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