Python App Course: session.run() vs session.read_transaction()

General Graph Academy
1

Hello,

I an doing the Graph Academy Course for Python Apps. Setting the environmental variables and building the connection went well.

But now I am struggling with read_transaction: In the following code the variable res1 is None (so nothing is printed), while res2 contains the names of the proper actors.

#Create a new Driver instance
driver = GraphDatabase.driver(neo4j_uri, auth=(neo4j_username, neo4j_password))

#Execute within a Read Transaction vs execute with session.run()
with driver.session() as session:
    def get_movies(tx, title):
        return tx.run("""
            MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
            WHERE m.title = $title 
            RETURN p.name AS name
            LIMIT 10
        """, title=title)    
    res1 = session.read_transaction(get_movies,title="Apollo 13")    
    for r in res1:   
        print(r["name"])

      
    res2 = session.run("""
            MATCH (p:Person)-[:ACTED_IN]->(m:Movie)
            WHERE m.title = $title 
            RETURN p.name AS name
            LIMIT 10
        """, title="Apollo 13")    
    for r in res2:
        print(r["name"])
        
    session.close()

Does anybody know where I am going wrong here?

Thanks in advance

1 Like
2

What's going wrong is that in the transaction function example (get_movies) you are passing the result object outside of the transaction function where it's no longer bound. In the session.run() case you're not using a transaction function.

Check this article: Neo4j Driver Best Practices - Neo4j Graph Data Platform and the heading in it titled " Process Database Results Within Your Transaction Function" and it will explain in detail what's happening here and why.