problem to access of the properties of an edge when using plpython3u in PostgreSQL to create functions

Question

I implement python function for for the following query and i get correct answer, but when i try to create functions in postgreSQL by using plpython3u extension, it doesn't have any error but still doesn't return the results to the table.

Also, I should mention that the following function works when i want return all the paths, i mean without considering the following part:

for i in range(len(flight) - 1):
     arrival_time = datetime.strptime(flight[i]["arrival_time"], '%Y-%m-%d %H:%M')
     next_departure_time=datetime.strptime(flight[i+1]"departure_time"], '%Y-%m-%d %H:%M')
     if arrival_time < next_departure_time:
            is_continuous = False
            break

That's why i think the problem is the how i want to access to the edge properties. anyone knows how can i fix it?

CREATE OR REPLACE FUNCTION graph.paircpath(
    origin text,
    edge text,
    destination text)
    RETURNS TABLE(city1 ag_catalog.agtype, airport1 ag_catalog.agtype, flight ag_catalog.agtype, airport2 ag_catalog.agtype, city2 ag_catalog.agtype) 
    LANGUAGE 'plpython3u'
    COST 100
    VOLATILE PARALLEL UNSAFE
    ROWS 1000

AS $BODY$
    from datetime import datetime
    import age
    import psycopg2

    def paircpath(origin, edge, destination):
        conn = psycopg2.connect(host="localhost", port="5432", dbname="postgres", user="postgres", password="13711992")
        with conn.cursor() as cursor:
            try:
                cursor.execute("SET search_path = ag_catalog, public, graph;")
                cursor.execute("LOAD 'age';")
                cursor.execute("GRANT USAGE ON SCHEMA ag_catalog TO postgres;")

                query = f"""SELECT * FROM cypher('graph', $$ 
                    MATCH (a)-[:LocatedAt*]->(c:City {{name: '{origin}'}})
                    MATCH (a:Airport)-[e:{edge}]->(b:Airport) 
                    MATCH (b)-[:LocatedAt*]->(c1:City {{name: '{destination}'}}) 
                    RETURN c, a, e, b, c1 
                $$) AS (city1 agtype, airport1 agtype, flight agtype, airport2 agtype, city2 agtype); """

                cursor.execute(query)
                paths = cursor.fetchall()

                for row in paths:
                    city1 = row[0]
                    airport1 = row[1]
                    flight = row[2]
                    airport2 = row[3]
                    city2 = row[4]
                    is_continuous = True
                    for i in range(len(flight) - 1):
                        arrival_time = datetime.strptime(flight[i]["arrival_time"], '%Y-%m-%d %H:%M')
                        next_departure_time = datetime.strptime(flight[i+1]["departure_time"], '%Y-%m-%d %H:%M')
                        if arrival_time < next_departure_time:
                            is_continuous = False
                            break
                    if is_continuous:
                        yield (city1, airport1, flight, airport2, city2)

            except Exception as ex:
                print(type(ex), ex)

    for result in paircpath(origin, edge, destination):
        yield result

$BODY$;

ALTER FUNCTION graph.paircpath(text, text, text)
    OWNER TO postgres;

The function doesn't return and just run like below: results

but by removing the condition:

for i in range(len(flight) - 1):
     arrival_time = datetime.strptime(flight[i]["arrival_time"], '%Y-%m-%d %H:%M')
     next_departure_time=datetime.strptime(flight[i+1]"departure_time"], '%Y-%m-%d %H:%M')
     if arrival_time < next_departure_time:
            is_continuous = False
            break

the function shows all the paths like below: results without condition

Answer 1

It seems like there is a problem in the way you are checking if the flight is continuous. Change the following code:

if arrival_time < next_departure_time:
    is_continuous = False
    break

to the code:

if arrival_time > next_departure_time:
    is_continuous = False
    break