Creating dynamic relation names with Java

I'm trying to create relations between already created nodes. I'm able to create normal relations (fixed names) without any problems but I'm not able to create relation names dynamically.

I explain:

I'm trying to replicate the model explained in this interesting website:

  1. I create Airports Nodes (success):"CREATE (a: Airport {airportCode: {airportCode}, countryName: {countryName}, cityName: {cityName}})", parameters("airportCode", airportCode, "countryName", countryName, "cityName", cityName));

  2. I create AirportDay Nodes (success):"CREATE (ad: AirportDay {Code: {Code}, AirportCode: {AirportCode}, DateCode: {DateCode}})", parameters("Code", code, "AirportCode", airportCode, "DateCode", dateCode));

  3. I create Leg (or Flight) Nodes (success)"CREATE (l: Leg {LegCode: {LegCode}, Origin: {Origin}, Destination: {Destination}, LegFlightNum: {LegFlightNum}, FlightNum: {FlightNum}, DepartureDate: {DepartureDate}, DepartureTime: {DepartureTime}, DepartureDateTime: {DepartureDateTime}, ArrivalDate: {ArrivalDate}, ArrivalTime: {ArrivalTime}, ArrivalDateTime: {ArrivalDateTime} })", parameters("LegCode", legCode, "Origin", origin, "Destination", destination, "LegFlightNum", legFlightNum, "FlightNum", flightNum, "DepartureDate", departureDate, "DepartureTime", departureTime, "DepartureDateTime", departureDateTime, "ArrivalDate", arrivalDate, "ArrivalTime", arrivalTime, "ArrivalDateTime", arrivalDateTime));

  4. I link correctly Airport & AirportDay (success):"MATCH (a:Airport), (ad:AirportDay) WHERE a.airportCode = ad.AirportCode MERGE (a)-[:HAS_DAY]->(ad)");

  5. I'm trying to link AirportDay & Leg but this way, relation names are not dynamic (I would like to have the name of the destination airport +_FLIGHT instead of HAS_FLIGHT):"MATCH (ad:AirportDay), (l:Leg) WHERE ad.DateCode = l.DepartureDate MERGE (ad)-[:HAS_FLIGHT]->(l)");

My problem is that the code from this website gives an example with an embedded Neo4j database, here is the code of this website:
departureAirportDayNode.createRelationshipTo(leg, RelationshipType.withName(arrivalCity + "_FLIGHT"));

But in my case, I'm using the Neo4J Java Driver and I found no example on how to deal with my problem.

I understand that I need to build the name of the relation dynamically but how to do this... ?

Any help will be appreciated,
(I'm a beginner with Neo4J and not an expert in Java...)
Don't hesitate if any information is missing.

Cypher on its own cannot use dynamic relationship types. However the apoc library solves this by call apoc.create.relationship(from, type, props, to)

if you use the java API you can also create relationships with:

Relationship rel = node1.createRelationshipTo(node2, RelationshipType.withName(relTypeName)

@stefan: Many thanks for these useful information. I will see if I can use APOC library.
@michael: Not sure what is the difference between using Java Driver code and Java API. I will read about this before commenting. Big thanks for your help.

Driver is client side in your own application.

Java API is if you write a procedure or server extension.