Update neo4j node with new relations, using py2neo

Question

My code adds nods and creates relations. It updates when the connection is a->b, a->c, a->d, it works(to node a new relations are added), but when I add connection f->a then a second node with name a is created. How can I make it to update the existing node a?

graph = Graph()
with open('test2') as fp:
    for line in fp:
        result = line.split('\t')
        category1 = graph.merge_one("Category", "name",result[0][result[0].rfind(':')+1:])
        category2 = graph.merge_one("Category", "name",result[1][result[1].rfind(':')+1:])
        print result[0][result[0].rfind(':')+1:] +"|"+result[1][result[1].rfind(':')+1:]
        graph.create_unique(Path(category1, "SubCategoryOf", category2))

My test files is:

Category:Wars_involving_Burma Category:Wars_by_country Category:Wars_involving_Burma Category:Military_history_of_Burma Category:Wars_involving_Burma Category:Foreign_relations_of_Burma Category:World_War_II Category:Wars_involving_Bulgaria Category:World_War_II Category:Wars_involving_Burma

In this example

Category:Wars_involving_Burma

is created twice.

Answer 1

When I run your example, I don't get a node twice. From your question I can't tell how many 'Category:...' you have in each line. From how you split the line I assumed it's always two. One possible issue is that you don't remove line endings, so one of your 'Category:Wars_involving_Burma' nodes might have a newline character at the end. Also what you pasted is space separated, not \t.

Here is a suggestion how to improve your code, assuming your file looks like http://paste.ubuntu.com/10874106/

graph = Graph()

with open('test2') as fp:
    for line in fp:
        # strip the line ending first, then split by whitespace
        # I assume every line has to category entries?
        result = line.rstrip().split()

        # getting the category name is easier and more readable like this
        category1 = graph.merge_one("Category", "name", result[0].split(':')[1])
        category2 = graph.merge_one("Category", "name", result[1].split(':')[1])

        print result[0].split(':')[1] + '\t' + result[1].split(':')[1]

        # you don't need a Path here        
        graph.create_unique((category1, "SubCategoryOf", category2))

In addition, if you want your "Category" nodes to be unique, you should have a uniqueness constraint on the "name" property of "Category" nodes.

Cypher:

CREATE CONSTRAINT ON (n:Category) ASSERT n.name IS UNIQUE

py2neo:

graph.schema.create_uniqueness_constraint('Category', 'name')