how to check if a node exists in NEO4J with py2neo

Question

I would like to insert in my python code, a verification as follows:

{`if (data.screen_name == node.screen_name) THEN {just create new relationship with new text} else {create new node with new relationship to text } `}

i need to Implement this algorithm in my source code

Answer 1

Option 1

Look for the node first with .find() (assuming you use neo4j 2.x with labels):

mynode = list(graph_db.find('mylabel', property_key='screen_name',
              property_value='foo'))

Check if somethink is found:

your_target_node = # you didn't specify where your target node comes from

# node found
if len(mynode) > 0:
    # you have at least 1 node with your property, add relationship
    # iterate if it's possible that you have more than 
    # one node with your property

    for the_node in mynode:
        # create relationship
        relationship = graph_db.create(
            (the_node, "LABEL", your_target_node, {"key": "value"})
        )

# no node found     
else:
    # create the node
    the_node, = graph_db.create({"key", "value"})

    # create relationship
    relationship = graph_db.create(
        (the_node, "LABEL", your_target_node, {"key": "value"})
    )

Option 2

Alternatively, have a look at get_or_create_path() to avoid the node lookup. But then you have to know your nodes and you need one as a py2neo Node instance. This might work if you always know/have the target node and want to create the start node:

path = one_node_of_path.get_or_create_path(
    "rel label",   {"start node key": start node value},
)

Answer 2

With the latest version of Py2Neo:

from py2neo import Graph, NodeMatcher
graph = Graph(url) #along with username and password
def nodeExist(lbl, node):
    matcher = NodeMatcher(graph)
    m = matcher.match(lbl, screen_name == node.screen_name).first()
    if m is None:
       return False
    else:
       return True