Hibernate OGM with MongoDB could not resolve property - mongodb

Question

This HQL query give me error:
String q4 = "SELECT i, COUNT(ie) FROM CorsoStudi cs \n"
+ "\t JOIN cs.inserogati ie JOIN ie.insegn i \n"
+ "\t WHERE cs.nome = 'Laurea in Informatica' \n"
+ "\t GROUP BY i";
The error is:
Exception in thread "main" java.lang.IllegalArgumentException: org.hibernate.QueryException: could not resolve property: insegn. of: component[_id,annierogazione,annoaccademico,crediti,discriminante,discriminantemodulo,hamoduli,id_facolta,insegn,inserogato_padre,modulo,nomemodulo,nomeunita,programma]
This is InsErogato:
#Embeddable
public class InsErogato {
private Integer _id;
private String annoaccademico;
#Embedded
private Insegn insegn;
#Embedded
private Discriminante discriminante;
private Integer modulo;
private String discriminantemodulo;
private String nomemodulo;
private Double crediti;
private String programma;
private Integer id_facolta;
private String hamoduli;
#Embedded
private InsErogatoPadre inserogato_padre;
private String nomeunita;
private Integer annierogazione;
// constructors, getters and setters and toString
}
and this is Insegn:
#Embeddable
public class Insegn {
private Integer _id;
private String nomeins;
private String codiceins;
// constructors, getters and setters and toString
}
Main:
// begin transaction
entityManager.getTransaction().begin();
List<Object[]> insegn = entityManager
.createQuery(q4, Object[].class)
.getResultList();
for(Object[] i : insegn) {
Insegn ins = (Insegn)i[0];
Long count = (Long)i[1];
System.out.println("nomeins: " + ins.getNomeins() + ", numero inserogati: " + count);
}
// commit transaction
entityManager.getTransaction().commit();
The MongoDB structure:
https://i.stack.imgur.com/qFusC.jpg
https://i.stack.imgur.com/k04HK.png
https://i.stack.imgur.com/H8nhS.png
https://i.stack.imgur.com/eYl2M.png
I tried to change the query but Hibernate doesn't find "insegn" (and also "discriminante") property in "inserogato", but he can find other simple attributes from it (like "annoaccademico" etc.).
The same query works on Hibernate ORM with PostgreSQL.
Maybe I have to add something in the annotations, or change the mongoDB structure (?).
I'm using Hibernate OGM 5.3.1.Final and MongoDB 3.6.3 JDBC Driver.

Answer 1

The same query works on Hibernate ORM with PostgreSQL
But PostgreSQL is a SQL database, MongoDB is a NoSQL database. Hibernate OGM is a means to add Hibernate ORM to NoSQL databases. The '(H)SQL' for OGM is limited (see below).
You don't say what your application is deployed on. I use WildFly 12.0.0.Final. I've had OGM with MongoDB working on version 11 & 12.
entityManager.getTransaction().begin();
I use the (WildFly) container to handle transactions. Annotate my EJB.
#TransactionManagement(TransactionManagementType.CONTAINER)
I don't believe you can use (H)SQL per se with Hiberate OGM but:
Use JPQL - only for simple queries for now
Use the NoSQL native query mapping the result as managed entities
Use Hibernate Search queries - primarily full-text queries
It says in the documentation:
In particular and of notice, what is not supported is:
cross entity joins
JPQL functions in particular aggregation functions like count
JPQL update and delete queries
One of my queries:
Query query = mongoDBEntityManager.createQuery("FROM FoodsCosmeticsMedicines f WHERE f.ean = :ean")
.setParameter("ean", ean);
The entity (the #Expose are for the JSON)
#Entity(name = "FoodsCosmeticsMedicines")
#Indexed
#Table(name = "foodsCosmeticsMedicines")
public class FoodsCosmeticsMedicines implements Serializable {
// Arrays of Objects
#Expose(deserialize = true, serialize = true)
#Embedded
ProductCharacteristics productCharacteristics;
#Expose(deserialize = true, serialize = true)
#Embedded
CalcNutrition calcNutrition;
#Expose(deserialize = true, serialize = true)
#Embedded
Nutrients nutrients;
#Expose(deserialize = true, serialize = true)
#Embedded
Enumbers enumbers;
#Expose(deserialize = true, serialize = true)
#Embedded
ChemicalsMineralsVitamins chemicalsMineralsVitamins;
#Expose(deserialize = true, serialize = true)
#Embedded
Lifestyle lifestyle;
.....
}
Why are you using JOIN?
With MySQL I use Hibernate as my ORM I would use annotations to map relationships with entities such as:
#OneToOne(cascade = CascadeType.ALL, mappedBy = "product", fetch = FetchType.LAZY)
private UriEntity uri;
entityManager.getTransaction().commit();
This is irrelevant as all you've done is read. Maybe you excluded the persist?
I'm sure you've read the documentation. I found all the answers to the problems I encountered here:
Hibernate OGM 5.3.1.Final: Reference Guide

Answer 2

Currently, queries with group by are not supported. You will need to run a native MongoDB query for this particular use case. See the reference documentation for more details about it.
I think the join on an embedded entity instead of a collection is confusing the parser even if it's a valid query. You should see a clearer exception with the following one (equivalent to the one you are trying):
SELECT ie.i, COUNT(ie)
FROM CorsoStudi cs
JOIN cs.inserogati ie
WHERE cs.nome = 'Laurea in Informatica'
GROUP BY ie.i;
It should throw:
java.lang.UnsupportedOperationException: The GROUP BY clause is not supported
Aggregate functions are not supported as well.