I want to create a new Role extending two existing roles. So is it possible in composer modelling language for a participant to extend multiple participants?
It is not likely to be supported as multiple inheritance is tricky and you would be forced into design issues in Object Oriented systems - Diamond Problem in multiple inheritance .
A Participant Type can only Extend one Participant type.
Using Concepts may allow you "re-use" elements of the model and ensure consistency.
concept Manager {
o String MTitle
o String QualificationType
}
concept Engineer {
o String ETitle
o String CharterCertType
}
participant Mgr identified by mID {
o String mID
o String name
o Manager manager
}
participant Engr identified by eID {
o String eID
o String name
o Engineer engineer
}
participant EMgr identified by emID {
o String emID
o String name
o Manager manager
o Engineer engineer
}
The modelling language is covered in Modelling Language and Model Compatibility
Related
I have the following model: a "classical" many-to-many book/author association but with 2 peculiarities.
Author does not have an association to Books.
The Author personal data is stored on other associated entity, called Person.
The model:
public class Book {
#ManyToMany
List<Author> authors;
}
public class Author {
#OneToOne
Person person;
}
public class Person {
String name;
}
I would like to write a service which, given a book, will return all the authors associated with it. I would also like to retrieve the personal data avoiding the N+1 problem.
Inside my Book repo I wrote a custom query like that:
#Query("select b.authors from Book b join b.authors a join fetch a.person where b = :book")
List<Author> listAuthors(#Param("book") Book book);
But I have the folloiwing error:
query specified join fetching, but the owner of the fetched
association was not present in the select list (...)
I could manage to solve it by adding the association to Books on the Author side and fetching Person from it. Unfortunately , in my case, it is really desirable that Authors do not know about Books.
Is there any way to fetch Person data from a Book?
This is actually a Hibernate Bug HHH-14116 - I recently stumbled across a related bug and in the discussion in the Hibernate Chat this bug was filed too. There is already a fix, but AFAIK it has not been released yet.
One way to circumvent this would be to have the relationship be bi-directional and query from the Author side.
Otherwise you could do it with a subquery, but I'm not sure whether that works with Spring Data JPA:
select a from Author a join fetch a.person where a.id in
(select a.id from Book b join b.authors a where b = :book)
Have you tried selecting Person with your #Query as well?
#Query("select b.authors, a.person from Book b join b.authors a join fetch a.person where b = :book")
List<Author> listAuthors(#Param("book") Book book);
I solved it using an EXISTS clause:
#Query("select a from Author a join fetch a.person " +
"where exists (select 1 from Book b where b = :book and a member of b.authors)")
List<Author> listAuthors(#Param("book") Book book);
This will not create a reference loop in modeling language, right?
participant Owner identified by name {
o String name
o Car[] cars
}
asset Car identified by plateNumber {
o String plateNumber
--> Owner owner
}
Correct - it won't. Your model simply creates an array of cars in participant class Owner and a relationship (identifier) to owner from the asset class Car. This is perfectly fine and reasonable as for as modeling goes and the circular nature of what you're asking.
I have defined Asset as :
asset PurchaseOrderAsset identified by orderId {
o String orderId
--> SupplierChainParticipant createdBy
--> SupplierChainParticipant assignedTo
o String description
o String status
o Integer quantity
o String assetId
o PurchaseOrderAsset[] subPurchaseOrders
}
Now, When I am trying to create Asset, I am getting error as "InternalError: too much recursion". i am facing this error in composer playground.
Can we have self-join relationship or not?
This is a bug, please create an issue for it, attaching your example BNA.
To workaround it I recommend that you create a concept for the line items of a purchase order. Conceptually those "sub" purchase orders are not assets, because they are not addressable through a registry.
Please also see: Different between 'o' and arrow symbol used in .cto file?
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 ?
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.
I want to do the following...
FROM o IN orders
SELECT new OrderContainer { Contact = (PostalContact) o.Contact }
So hopefully you can see that the order's 'Contact' will be of a derived type. Unfortunately however it doesn't seem to do a polymorphic fetch! Is there anyway of achieving this?
Cheers, Ian.
Try using the extention method .OfType()
from o in orders
select new OrderContainer { Contact = o.Contact.OfType<PostalContact>().FirstOrDefault() }
Edit:
a way to get the full object data, but i doubt that this is good enough for your needs.
from c in contacts.OfType<PostalContact>()
where c.Orders.Any(o=>o.Contact.Id == c.id)
select new OrderContainer { Contact = c }
on the other hand, if you set the base class (entity) to abstract, you may find that entity will load the full objects. but this is not recomended due to the queries that are generated. if you are looking into this you may want to look at (TPH) Table per Hierarchy for your contacts