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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).

Why is JPA retrieving one column using a seperate select

Problem description
Hello, I've been using OpenJPA 2.1.2 (JPA 2.0) to retrieve data from a table called LOGISCHRAPPORTwhich has about 28 columns. In some cases OpenJPA decides to issue seperate select statements for one of the columns for no particular reason, leading to a dramatic decrease in query performance.
Everything is fine until...
Initially everything goes fine and all my columns are retrieved in a performant, single SELECT statement by JPA.
As soon as I add a relationship to another entity called RAPTAALMETADATA
#OneToMany(fetch=FetchType.EAGER, cascade = CascadeType.ALL)
#JoinColumns({
#JoinColumn(name = "RAPPORTNR", referencedColumnName = "RAPPORTNR"),
#JoinColumn(name = "RAPPORTTYPE", referencedColumnName = "RAPPORTTYPE") })
private List<Raptaalmetadata> raptaalmetadata;
---
Queried using Criteria API as follows:
---
Join<LogischRapport, Raptaalmetadata> metadata = reportRoot.join(
"raptaalmetadata");
JPA no longer includes one of my original columns called REPORT_COMMENTS instead it is issuing separate select statements to retrieve the REPORT_COMMENTS column for each instance of LOGISCHRAPPORT. All other columns (including the ones coming from RAPTAALMETADATA are retrieved properly as part of the intial SELECT.
REPORT_COMMENTS is of the HUGEBLOB type in Oracle and I've mapped in in my Entity as follows:
#Lob
#Basic
#Column(name = "REPORT_COMMENTS")
private byte[] reportComments;
I now get tons of these:
SELECT t0.REPORT_COMMENTS
FROM dwhsd001.LogischRapport t0
WHERE t0.rapportnr = ? AND t0.rapporttype = ?
[params=(long) 1473, (String) RAP]
Can anyone point out why I might be seeing this behavior and how I can avoid it?
Its not a LAZY loading problem as I've specifically tested that case. I don't see any other reason why OpenJPA decides to retrieve this one column using separate statements.
Update 1
Interesting addition: as soon as I remove the fetch=FetchType.EAGER attribute from the #OneToMany annotation described above I start seeing the exact same behavior for the relationship as I've been getting for the REPORT_COMMENTS column. This means I'm also getting separate SELECT statements for retrieving the entity relationship on top of the seperate selects for the column thereby further degrading performance.
In other words I'm then also getting tons of these:
SELECT t0.isotaalcode, t0.rapportnr, t0.rapporttype,
t0.FUNCDESC_MODIFIED_BY, t0.FUNCDESC_MODIFIED_DATE,
t0.FUNCTIONAL_DESCRIPTION, t0.omschrijving, t0.titel
FROM dwhsd001.Raptaalmetadata t0
WHERE t0.rapportnr = ? AND t0.rapporttype = ?

Multiple fetches with EAGER type in Hibernate with JPA

I have an entity which contains:
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "assessment")
#OrderBy(value = "order ASC")
private List<AssessmentPart> assessmentParts = new LinkedList<>();
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "assessment")
private List<AssessmentText> texts = new LinkedList<>();
as you see there are two collections which needs to be eagerly loaded. This is not working and hibernate throws an exception:
Caused by: org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags
That's because Hibernate can't fetch multiple collections with one go. But if I change the List to Set and the LinkedList to HashSet this part works fine but the other - more annoying issue occurs.
When I am trying to get the entity from the database using:
entityManager.find(entityClass, primaryKey);
It fails with:
org.hibernate.AssertionFailure: null identifier
I am sure that ID I am passing to find method is not null, I've debugged and I am sure of this. It somehow disappears inside Hibernate.
If I change collection types to LAZY everything just works without errors but there are some circumstances where I need to use EAGER.
Does anybody have a solution how to fix it? Either I could have a set but prevent assertion error from occurring or I could have a list but somehow avoid multiple fetch bags error.
I am using:
Hibernate 4.2.2.Final
Tomcat 7
JPA 2.0
JDK 1.7
EDIT
I've just discovered that adding #Fetch(FetchMode.SELECT) fixes the issue and I can use multiple list with EAGER type, but is there anyway to solve this by not using Hibernate specific annotations? And why it fixed the issue in the first place?

The root cause of the problem is that when Hibernate fetches SQL query results there is no simple way to tell which child element belongs to which collection. See this blog entry for more detailed explanation with an example. To summarize you have following workarounds:
Load each collection separately using subselect #Fetch(FetchMode.SELECT)
Force usage of list instead of bag by adding index column #IndexColumn(name="LIST_INDEX")
Use unordered collection like Set.

If you are using Hibernate and you do not care using Hibernate annotations :
Annotate your collection fields with:
#LazyCollection(LazyCollectionOption.FALSE)
Remember to remove the fetchType attribute from the #OneToMany annotation.

Hibernate: Many To Many Relation with attributes: correct configuration with Annotations

I have a problem with Hibernate (Thanks to Thomas now the problem is more legible).
In Short:
How to configure a ManyToMany association with Hibernate when the relationship has an attribute and we need save, delete and update in cascade?
In Large:
Imagine the following DataBase:
User Profile
M______N
|
attribute
There are 3 tables here:
"User", "Profile" and "User_Profile".
Now imagine User_Profile has 1 attribute for the relation (and obviously the keys).
Ok, now this is translating to Hibernate by the following:
User:
// The relation is Many to Many, but considering that it has an attribute, this is OneToMany with the ManyMany RelationShip
#OneToMany(mappedBy="user", targetEntity=UserProfile.class)
#Cascade({CascadeType.SAVE_UPDATE, CascadeType.DELETE})
#LazyCollection(LazyCollectionOption.TRUE)
private Set<UserProfile> userProfile = new HashSet<UserProfile>();
UserProfile:
#Id
#ManyToOne(targetEntity=User.class,fetch=FetchType.LAZY)
#Cascade({CascadeType.LOCK})
#JoinColumns({ #JoinColumn(name="...", referencedColumnName="...") })
private User user;
#Id
#ManyToOne(targetEntity=Profile.class,fetch=FetchType.LAZY)
#Cascade({CascadeType.LOCK})
#JoinColumns({ #JoinColumn(name="...", referencedColumnName="...") })
private Profile profile;
So, I think the configuration is correct, and the save, independently if the User has Profile childrens save all of them. The problem is when I try to update the user:
getHibernateTemplate().getSessionFactory().getCurrentSession().clear();
getHibernateTemplate().saveOrUpdate( user );
getHibernateTemplate().getSessionFactory().getCurrentSession().flush();
Hibernate don´t delete the Profile relation if there is an empty set of Profile childrens. Only add the profiles (override the old)... That´s rare... What´s the problem?
Thank you in advance

All you actually do is remove the relation and thus theres no DELETE to cascade, that's why nothing gets deleted.
Try adding the Hibernate cascade type DELETE_ORPHAN (using the #Cascade annotation) to make Hibernate delete entities that are not referenced anymore.
Additionally, I'd not remove the Mini entities alone. If there's no relation, i.e. the set of Minis is empty, it normally makes no sense to keep the SuperMini entities that now represent an empty collection (in rare cases it might make sense, just want you to think about whether you need them or not).
Edit:
Note that with DELETE_ORPHAN you should reuse the set, otherwise all the relations might be deleted and reinserted.
Basically Hibernate would then see the set being changed and would issue a delete for the "old" set and a reinsert for the "new" set. This could be wanted but in case you only want an update, i.e. only delete the entities that are not in the set anymore, you should do the following:
clear the set
add the "new" set to the reused and now cleared set using addAll(...)
This should trigger the update (and deletion of orphans) only.

How to batch delete using bulkUpdate

I have a common User / Role setup, with a user_role join table. I'm trying to use Spring's HibernateTemplate to mass delete all locked users like this:
getHibernateTemplate().bulkUpdate("delete from User where locked=?", true);
If the user being deleted does not have any roles (no record in the user_role table), then everything goes fine; however if the user does have a role record, I'm getting the following error:
integrity constraint violated - child
record found
Roles are defined in User.java like this:
#ManyToMany(fetch = FetchType.EAGER)
#JoinTable(name = "user_role", joinColumns = { #JoinColumn(name = "user_id") }, inverseJoinColumns = #JoinColumn(name = "role_id"))
private Set<Role> roles = new HashSet<Role>();
So how can I batch delete users even if a user has child records? Thanks!

Bulk delete operations are not cascaded to related entities as per the JPA specification:
4.10 Bulk Update and Delete Operations
Bulk update and delete operations
apply to entities of a single entity
class (together with its subclasses,
if any). Only one entity abstract
schema type may be specified in the
FROM or UPDATE clause.
...
A delete operation only applies to
entities of the specified class and
its subclasses. It does not cascade
to related entities.
However, I'd expect the JPA provider to deal with join tables. Sadly, Hibernate doesn't and this is logged in HHH-1917. I'm afraid you'll have to fall back on native SQL to clean up the join table yourself or to use cascading foreign keys in the schema.

Application-level cascading (cascading through hibernate annotations or JPA annotations) only work if the actual entity is actually loaded from the db. When you use the hibernate template with HQL, you'll notice that the entities are not loaded, and the HQL is directly converted to SQL to be executed.
If you want to batch delete you have to use an HQL query to delete all relevant tables (ie roles) before deleting the parent table data.

I'm not entirely sure because it's hard for me to recreate this problem, but I think you might need to add a cascade to your #ManyToMany
#ManyToMany(cascade = CascadeType.ALL)

Since you want to bulk delete something that have a ManyToMany related items, you first have to delete the relation (in the join table), or do a loop and for each item, delete manually (insane and too much heavy).
So, since JPQL does not allow to do it, a possible way is to make a native SQL query for deleting the id you want in the related table, and then, do the bulk delete.