Upgrade of spring data neo4j 3.x to 4.x Relationship Operations - spring

Question

In Spring data neo4j 3.x To create relation ship between two nodes and relationship contains set of properties earlier used to achieve this by apis
create :
n4jOperations.createRelationshipBetween(Object start, Object end, Class<R> relationshipEntityClass, String relationshipType, boolean allowDuplicates);
delete:
n4jOperations.deleteRelationshipBetween(Object start, Object end, String type);
get:
n4jOperations.getRelationshipBetween( from, to, relationshipClass, relationshipType );
But after migration i didnt't find above apis
as per docs says
#NodeEntity
public class Student {
private String name;
#Relationship(type = "ENROLLED")
private Set<Enrollment> enrollments;
}
By repo.save(Student);
//Relation creation was possible but new api's how can i achieve below use cases
1.How can avoid duplicate relation creation?
2.get Relation ship between two nodes ?
2.delete relation ship between two nodes ?

Answer 1

SDN 4 does not provide low-level graph-operations like setting nodes and relationships directly.
Relationships in the graph are modelled and manipulated using object references in your domain classes. They come in two flavours: implicit and explicit. Implicit relationships are described by simple references between two node entities, e.g. Customer and Address:
class Customer {
#Relationship(type="LIVES_AT")
Address address; // implied (:Customer)-[:LIVES_AT]->(:Address)
...
}
Explicit relationships are modelled using RelationshipEntity objects, and are allowed to have properties (but don't have to). They are still accessed as references in your domain model.
class Person {
#Relationship(type="RATED")
List<Rating> ratings
}
class Movie {
}
#RelationshipEntity(type="RATED")
class Rating {
#StartNode Person person;
#EndNode Movie movie;
int stars;
}
Note: If you don't need properties on a particular relationship, you don't need to use a RelationshipEntity.
To answer your specific questions:
1) SDN 4.0 doesn't create duplicate relationships. No matter how many times you persist a specific object reference, it will represented by only one relationship in the graph.
2) Hopefully that is clear now!
3) Setting an object reference to null and saving the parent object will remove the relationship. Or, if the reference is part of Collection, remove it from the collection. You must ensure that the object references are removed from both sides. For example if A holds a reference to B and B holds a reference to A, you must remove A's reference to B as well as B's reference to A.