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Hibernate JPA Meta Model -- reference nested properties?

Suppose an entity model where an Employee has a Supervisor who has an id. Using hibernate-jpamodelgen to generate the meta model for the entities, how can I query a nested field?
For instance, "get all employees whose supervisor has id 4", using JpaSpecificationExecutor:
Page<Employee> getEmployeesBySupervisorId(int id) {
return findAll((root, query, criteriaBuilder) -> {
return criteriaBuilder.equal(root.get(Employee_.supervisor.id), id);
});
}
Note that Employee_ is the model meta class for Employee (and was generated by Hibernate).
This code will produce an error because the id symbol cannot be found on type SingularAttribute<Employee, Supervisor>. I get that, but it seems like these should somehow be chainable. I can't find great examples of how to do this cleanly.

In order to navigate to related entities, you must use From#join() join method, which works well with MetaModel:
CriteriaQuery<Employee> cq = criteriaBuilder.createQuery(Employee.class);
Root<Employee> from = cq.from(Employee.class);
Predicate p = criteriaBuilder.equal(from.join(Employee_.supervisor).get(Supervisor_.id), id);
See also
Oracle's Java EE Tutorial - Using the Criteria API and Metamodel API to Create Basic Typesafe Queries

Yes, I also stumbled upon this problem that the Metamodel classes are not offering deeper visibility to relationships > 1.
While accessing A.b is possible, A.b.c is not.
But there is another possibility besides Joins:
Just concatenate by using several getter(). For this you will need a root element (= CriteriaQuery & CriteriaBuilder).
return criteriaBuilder.equal(root.get(Employee_.supervisor).get(Supervisor_.id), id);
While this still ensures type safety, the whole path should be correct as it is not validated until runtime.
Also for sorting a resultset using the Metamodel there is a similar solution. Say you want to sort by the Supervisor's id:
Use JpaSort and JpaSort.Path
JpaSort.of(JpaSort.Direction.ASC, JpaSort.path(Employee_.supervisor).dot(Supervisor_.id));

Hibernate is making extra SQL statement with #ManyToOne and #Lazy fetching object

I would like someone to explain me why Hibernate is making one extra SQL statement in my straight forward case. Basically i have this object:
#Entity
class ConfigurationTechLog (
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
val id: Long?,
val configurationId: Long,
val type: String,
val value: String?
) {
#JsonIgnore
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "configurationId", insertable = false, updatable = false)
val configuration: Configuration? = null
}
So as you can see, nothing special there. And when i execute this query :
#Query(value = "SELECT c FROM ConfigurationTechLog c where c.id = 10")
fun findById10() : Set<ConfigurationTechLog>
In my console i see this:
Hibernate:
/* SELECT
c
FROM
ConfigurationTechLog c
where
c.id = 10 */ select
configurat0_.id as id1_2_,
configurat0_.configuration_id as configur2_2_,
configurat0_.type as type3_2_,
configurat0_.value as value4_2_
from
configuration_tech_log configurat0_
where
configurat0_.id=10
Hibernate:
select
configurat0_.id as id1_0_0_,
configurat0_.branch_code as branch_c2_0_0_,
configurat0_.country as country3_0_0_,
configurat0_.merchant_name as merchant4_0_0_,
configurat0_.merchant_number as merchant5_0_0_,
configurat0_.org as org6_0_0_,
configurat0_.outlet_id as outlet_i7_0_0_,
configurat0_.platform_merchant_account_name as platform8_0_0_,
configurat0_.store_type as store_ty9_0_0_,
configurat0_.terminal_count as termina10_0_0_
from
configuration configurat0_
where
configurat0_.id=?
Can someone please explain me, what is happening here ? From where this second query is coming from ?

I assume you are using Kotlin data class. The kotlin data class would generate toString, hashCode and equals methods utilizing all the member fields. So if you are using the returned values in your code in a way that results in calling of any of these method may cause this issue.
BTW, using Kotlin data claases is against the basic requirements for JPA Entity as data classes are final classes having final members.

In order to make an association lazy, Hibernate has to create a proxy instance instead of using the real object, i.e. it needs to create an instance of dynamically generated subclass of the association class.
Since in Kotlin all classes are final by default, Hibernate cannot subclass it so it has to create the real object and initialize the association right away. In order to verify this, try declaring the Configuration class as open.
To solve this without the need to explicitly declare all entities open, it is easier to do it via the kotlin-allopen compiler plugin.

This Link can be useful for understand what kind (common) problem is that N + 1 Problem
Let me give you an example:
I have three Courses and each of them have Students related.
I would like to perform a "SELECT * FROM Courses". This is the first query that i want (+ 1) but Hibernate in background, in order to get details about Students for each Course that select * given to us, will execute three more queries, one for each course (N, there are three Course coming from select *). In the end i will see 4 queries into Hibernate Logs
Considering the example before, probably this is what happen in your case: You execute the first query that you want, getting Configuration Id = 10 but after, Hibernate, will take the entity related to this Configuration, then a new query is executed to get this related entity.
This problem should be related in specific to Relationships (of course) and LAZY Fetch. This is not a problem that you have caused but is an Hibernate Performance Issue with LAZY Fetch, consider it a sort of bug or a default behaviour
To solve this kind of problem, i don't know if will be in your case but ... i know three ways:
EAGER Fetch Type (but not the most good option)
Query with JOIN FETCH between Courses and Students
Creating EntityGraph Object that rappresent the Course and SubGraph that rappresent Students and is added to EntityGraph

Looking at your question, it seems like an expected behavior.
Since you've set up configuration to fetch lazily with #ManyToOne(fetch = FetchType.LAZY), the first sql just queries the other variables. When you try to access the configuration object, hibernate queries the db again. That's what lazy fetching is. If you'd like Hibernate to use joins and fetch all values at once, try setting #ManyToOne(fetch = FetchType.EAGER).

distinct inner join hql

I've the following hibernate entities
public class Container {
...
#OneToMany
private List<ACLEntry> aclEntries;
}
For securing my container instances i use the following entity:
public class ACLEntry {
...
private Long sid;
private boolean principal;
private Integer mask;
}
The hql-queries will be created automatically so for searching container instances,
the following query will be created:
select container from Container container
inner join container.aclEntries as aclEntry
with bitwise_and (aclEntry.mask, 1) = 1 and
(aclEntry.sid = :userId or aclEntry.sid = :roleId)
The problem with this is, that the aclentry join could return 2 results which will result in duplicate container results.
Has anyone an idea how to solve this ?

As far as I understood the problem you need a container that can hold multiple entries of your Container object just replace your hql query with the following one:
With adding select distinct as native query.

As a brute force solution, you could write a native query.

It might make more sense to write this as a Criteria query, which easily supports selecting an object based on conditions of it's associations.
The same thing can be done in HQL or a native query, it might be instructive to execute a Criteria query specifying the same logic and just see what HQL/SQL it generates.

How to bulk delete from element collection in jpa

I'm using jpa 2.0 and I have the following entity:
#Entity
public class Folder{
#ElementCollection
#CollectionTable(name="folder_files")
private Set<String> files;
// .....
}
Given a file name, I would like to delete all entries where files == theGivenFileName. In sql it would be something like this:
Delete from folder_files where files = XXX
Is there a way to perform this query using criteria-api?
If not, is there a way to perform this query using jpql?
UPDATE:
I think my question was not clear enough:
Since jpql uses entities (and not tables) I cannot just perform the sql written above plus since I'm using #ElementCollection I don't know how to address this variablr or even deal with it. I would like to delete all entries in that collection (in my case, the files set) which holds a given value, from all entities. Is that possible using jpql or (even better) criteria-api?

The Delete FROM clause requires an Entity, so there is no way to delete from an element collection from what I understand.
You can use a native SQL query, or you can map the element collection as a OneToMany to an Entity instead.

You can use the like query just the syntax is slightly changed.
query = em.createQuery("SELECT i FROM Item i WHERE UPPER(i.name) LIKE :keyword ");
query.setParameter("keyword", "%" + keyword.toUpperCase() + "%");
You can read more on following link,
https://forums.oracle.com/forums/thread.jspa?threadID=423742
Updated:
#Noam you can do it: Like in Criteria API
List cats = sess.createCriteria(Cat.class)
.add( Restrictions.like("name", "Fritz%") )
.add( Restrictions.between("weight", minWeight, maxWeight) )
.list();
Kindly read more on it at following link:
http://ctpconsulting.github.com/query/1.0.0.Alpha3/criteria.html
http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/querycriteria.html

This cannot be done. Via JPQL it does not work because DELETE statement can only be applied to entities. Excerpt from JPA 2.0 specification:
Bulk update and delete operations apply to entities of a single entity
class (together with its subclasses,if any).
...
delete_statement ::= delete_clause [where_clause]
delete_clause ::= DELETE FROM entity_name [[AS] identification_variable]
Also it doesn't work via Criteria API. CriteriaQuery supports only selecting - not updates or removals.
You have to go for native SQL.

JPA Criteria API - How to add JOIN clause (as general sentence as possible)

I am trying to construct queries dynamically, and my next target is add JOIN clauses (I don't know how can I use the API).
By now, for example, this code work for me :
...
Class baseClass;
...
CriteriaBuilder cb = JpaHandle.get().getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery(this.baseClass);
Root entity_ = cq.from(this.baseClass);
Predicate restrictions = null;
...
restrictions = cb.conjunction();
restrictions = cb.and(restrictions, entity_.get("id").in(this.listId));
...
cq.where(restrictions);
...
Query qry = JpaHandle.get().createQuery(cq);
(Note : JpaHandle is from wicket-JPA implementation)
My desire is add JOIN clause (as generical as possible)!
I have the particular annotations in the classes (this.baseClass)
For example :
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "assay_id", nullable = false)
So,Is there a way to something like this in standard JPA ? (Note : this don't compile)
Here a practical fail aproaches :
...
Join<Experiment,Assay> experimentAssays = entity_.join( entity_.get("assay_id") );
Or like that :
...
CriteriaQuery<Customer> q = cb.createQuery(Customer.class);
Root<Customer> c = q.from(Customer.class);
SetJoin<Customer, PurchaseOrder> o = c.join(Customer_.orders);
For me, if it could be more generical as possible it will be great... :
...
Join joinClause = entity_join(entity_.get("assay_id"), entity2_.get("id"));
Of course, I have the particular annotations in the classes (this.baseClass)
Thank you for your time. I'll appreciate all kind of comments!

Maybe the following extract from the Chapter 23 - Using the Criteria API to Create Queries of the Java EE 6 tutorial will throw some light (actually, I suggest reading the whole Chapter 23):
Querying Relationships Using Joins
For queries that navigate to related
entity classes, the query must define
a join to the related entity by
calling one of the From.join methods
on the query root object, or another
join object. The join methods are
similar to the JOIN keyword in JPQL.
The target of the join uses the
Metamodel class of type
EntityType<T> to specify the
persistent field or property of the
joined entity.
The join methods return an object of
type Join<X, Y>, where X is the
source entity and Y is the target of
the join.
Example 23-10 Joining a Query
CriteriaQuery<Pet> cq = cb.createQuery(Pet.class);
Metamodel m = em.getMetamodel();
EntityType<Pet> Pet_ = m.entity(Pet.class);
Root<Pet> pet = cq.from(Pet.class);
Join<Pet, Owner> owner = pet.join(Pet_.owners);
Joins can be chained together to
navigate to related entities of the
target entity without having to create
a Join<X, Y> instance for each join.
Example 23-11 Chaining Joins Together
in a Query
CriteriaQuery<Pet> cq = cb.createQuery(Pet.class);
Metamodel m = em.getMetamodel();
EntityType<Pet> Pet_ = m.entity(Pet.class);
EntityType<Owner> Owner_ = m.entity(Owner.class);
Root<Pet> pet = cq.from(Pet.class);
Join<Owner, Address> address = cq.join(Pet_.owners).join(Owner_.addresses);
That being said, I have some additional remarks:
First, the following line in your code:
Root entity_ = cq.from(this.baseClass);
Makes me think that you somehow missed the Static Metamodel Classes part. Metamodel classes such as Pet_ in the quoted example are used to describe the meta information of a persistent class. They are typically generated using an annotation processor (canonical metamodel classes) or can be written by the developer (non-canonical metamodel). But your syntax looks weird, I think you are trying to mimic something that you missed.
Second, I really think you should forget this assay_id foreign key, you're on the wrong path here. You really need to start to think object and association, not tables and columns.
Third, I'm not really sure to understand what you mean exactly by adding a JOIN clause as generical as possible and what your object model looks like, since you didn't provide it (see previous point). It's thus just impossible to answer your question more precisely.
To sum up, I think you need to read a bit more about JPA 2.0 Criteria and Metamodel API and I warmly recommend the resources below as a starting point.
See also
the section 6.2.1 Static Metamodel Classes in the JPA 2.0 specification
Dynamic, typesafe queries in JPA 2.0
Using the Criteria API and Metamodel API to Create Basic Type-Safe Queries
Related question
How to generate JPA 2.0 metamodel?

Actually you don't have to deal with the static metamodel if you had your annotations right.
With the following entities :
#Entity
public class Pet {
#Id
protected Long id;
protected String name;
protected String color;
#ManyToOne
protected Set<Owner> owners;
}
#Entity
public class Owner {
#Id
protected Long id;
protected String name;
}
You can use this :
CriteriaQuery<Pet> cq = cb.createQuery(Pet.class);
Metamodel m = em.getMetamodel();
EntityType<Pet> petMetaModel = m.entity(Pet.class);
Root<Pet> pet = cq.from(Pet.class);
Join<Pet, Owner> owner = pet.join(petMetaModel.getSet("owners", Owner.class));

Warning! There's a numbers of errors on the Sun JPA 2 example and the resulting pasted content in Pascal's answer. Please consult this post.
This post and the Sun Java EE 6 JPA 2 example really held back my comprehension of JPA 2. After plowing through the Hibernate and OpenJPA manuals and thinking that I had a good understanding of JPA 2, I still got confused afterwards when returning to this post.

You don't need to learn JPA. You can use my easy-criteria for JPA2 (https://sourceforge.net/projects/easy-criteria/files/). Here is the example
CriteriaComposer<Pet> petCriteria CriteriaComposer.from(Pet.class).
where(Pet_.type, EQUAL, "Cat").join(Pet_.owner).where(Ower_.name,EQUAL, "foo");
List<Pet> result = CriteriaProcessor.findAllEntiry(petCriteria);
OR
List<Tuple> result = CriteriaProcessor.findAllTuple(petCriteria);