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Multi query for a join using hibernate criteriabuilder

I would like perform a join query using hibernate criteria API and map some of the joined fields explicitly.
This is pretty straightforward, so my code resulted in :
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Country> criteria = builder.createQuery(Country.class);
Root<Country> root = criteria.from(Country.class);
Join<Country, Translation> join = root.join("translatedName");
criteria.multiselect(root, join.get("fr"));
TypedQuery<Country> tq = session.createQuery(criteria);
List<Country> countries = tq.getResultList();
Country Entity
#Entity
#Table(name = "countries")
public class Country {
#Id
#Column
private UUID id;
#OneToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "name_id")
private Translation translatedName;
#Transient
private String name;
public Country(Country c, String name) {
this.id = c.id;
this.name = name;
}
//getters...
}
Translation Entity
package database.models;
import service.model.Country;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;
#Entity
#Table(name = "translations")
public class Translation {
#Id
private String id;
private String fr;
private String en;
// getters/setters
}
This does exactly what I want. Multiselect statement pass to my constructor the joined field, and I store it in the right variable.
However, I encountered the infamous N+1 select problem :
Hibernate: select country0_.id as col_0_0_, translatio1_.id as col_1_0_, translatio1_.fr as col_2_0_ from countries country0_ inner join translations translatio1_ on country0_.name_id=translatio1_.id
Hibernate: select country0_.id as id1_0_0_, country0_.name_id as name_id2_0_0_ from countries country0_ where country0_.id=?
...
After some research, I have found that using the fetch statement instead of join solves this issue. Updated code :
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaQuery<Country> criteria = builder.createQuery(Country.class);
Root<Country> root = criteria.from(Country.class);
Join<Country, Translation> join = (Join)root.fetch("translatedName");
criteria.multiselect(root, join.get("fr"));
TypedQuery<Country> tq = session.createQuery(criteria);
List<Country> countries = tq.getResultList();
The query fails with the following (well-known) QueryException :
Caused by: org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list [FromElement{explicit,not a collection join,fetch join,fetch non-lazy properties,classAlias=generatedAlias1,role=service.model.Country.translatedName,tableName=translations,tableAlias=translatio1_,origin=countries country0_,columns={country0_.name_id ,className=database.models.Translation}}]
I've come to understand that DTO Projection that I use for mapping my custom field, and the join fetch are not compatible.
For the record, I don't even need my translatedName relationship to be fetched. I just want to extract the right language and map it in my entity.
Thanks in advance. Any advice ?
The main purpose here is having a field name from my country filled with the translation, and return it directly to the user instead of having a nested field with all the translation available.
For example, if I receive a query with lang=fr, I want to return :
{
"name": "fr_name"
}
And not
{
"name": {
"fr": "fr_name",
"en": "en_name"
}
}
And I dont want having to iterate through my result set to map it manually for performance reason

Hibernate: projection JPQL query to DTO issue

To start with, I'll list three models that I work with in a query
ProductEntity:
#Entity
#Table(name = "product")
public class ProductEntity extends BaseEntity {
//some fields
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "owner_id")
private PartnerEntity owner;
#OneToMany(
mappedBy = "product",
fetch = FetchType.LAZY
)
private List<StockProductInfoEntity> stocks;
}
PartnerEntity:
#Entity
#Table(name = "partner")
public class PartnerEntity extends AbstractDetails {
//some fields
#OneToMany(
mappedBy = "owner",
fetch = FetchType.LAZY
)
private List<ProductEntity> products;
}
and StockProductInfoEntity:
#Entity
#Table(name = "stock_product")
public class StockProductInfoEntity extends BaseEntity {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "product_id")
private ProductEntity product;
//other fields
#Column(name = "rest")
private int rest;
}
And i want to fetch from database product with partner + calculate count in all stocks.
For convenience, I created a simple DTO:
#Getter
#AllArgsConstructor
public class ProductCountDTO {
private ProductEntity productEntity;
private int count;
//hack for hibernate
public ProductCountDTO(ProductEntity productEntity, long count) {
this.productEntity = productEntity;
this.count = (int) count;
}
}
and write JPQL query in JPA repository:
#Query("select new ru.oral.market.persistence.entity.product.util.ProductCountDTO(p, sum(stocks.rest))"+
" from ProductEntity p" +
" join fetch p.owner owner" +
" join p.stocks stocks" +
" where p.id = :id" +
" group by p, owner")
Optional<ProductCountDTO> findProductWithCount(#Param("id") long id);
But my application did not even start because of a problem with the query validation. I get this message:
Caused by: org.hibernate.QueryException: query specified join
fetching, but the owner of the fetched association was not present in
the select list
Very strange, but I tried to replace join fetch -> join.
And I understood why I got this error, hibernate made such a query to the database:
select
productent0_.id as col_0_0_,
sum(stocks2_.rest) as col_1_0_
from
product productent0_
inner join
partner partnerent1_
on productent0_.owner_id=partnerent1_.user_id
inner join
stock_product stocks2_
on productent0_.id=stocks2_.product_id
where
productent0_.id=?
group by
productent0_.id ,
partnerent1_.user_id
But why does he only take the product id and nothing else?
This query with Tuple work and get all fields from product and partner
#Query("select p, sum(stocks.rest) from ProductEntity p" +
" join fetch p.owner owner" +
" join p.stocks stocks" +
" where p.id = :id" +
" group by p, owner")
Optional<Tuple> findProductWithCount(#Param("id") long id);
And this produced native query what i want:
select
productent0_.id as col_0_0_,
sum(stocks2_.rest) as col_1_0_,
partnerent1_.user_id as user_id31_12_1_,
productent0_.id as id1_14_0_,
productent0_.brand_id as brand_i17_14_0_,
productent0_.commission_volume as commissi2_14_0_,
productent0_.created as created3_14_0_,
productent0_.description as descript4_14_0_,
productent0_.height as height5_14_0_,
productent0_.length as length6_14_0_,
productent0_.long_description as long_des7_14_0_,
productent0_.name as name8_14_0_,
productent0_.old_price as old_pric9_14_0_,
productent0_.owner_id as owner_i18_14_0_,
productent0_.pitctures as pitctur10_14_0_,
productent0_.price as price11_14_0_,
productent0_.status as status12_14_0_,
productent0_.updated as updated13_14_0_,
productent0_.vendor_code as vendor_14_14_0_,
productent0_.weight as weight15_14_0_,
productent0_.width as width16_14_0_,
partnerent1_.about_company as about_co1_12_1_,
partnerent1_.bik as bik2_12_1_,
partnerent1_.bank_inn as bank_inn3_12_1_,
partnerent1_.bank_kpp as bank_kpp4_12_1_,
partnerent1_.bank as bank5_12_1_,
partnerent1_.bank_address as bank_add6_12_1_,
partnerent1_.checking_account as checking7_12_1_,
partnerent1_.correspondent_account as correspo8_12_1_,
partnerent1_.company_name as company_9_12_1_,
partnerent1_.company_inn as company10_12_1_,
partnerent1_.company_kpp as company11_12_1_,
partnerent1_.ogrn as ogrn12_12_1_,
partnerent1_.okato as okato13_12_1_,
partnerent1_.actual_address as actual_14_12_1_,
partnerent1_.director as directo15_12_1_,
partnerent1_.full_name as full_na16_12_1_,
partnerent1_.legal_address as legal_a17_12_1_,
partnerent1_.short_name as short_n18_12_1_,
partnerent1_.country as country19_12_1_,
partnerent1_.discount_conditions as discoun20_12_1_,
partnerent1_.discounts as discoun21_12_1_,
partnerent1_.logo as logo22_12_1_,
partnerent1_.min_amount_order as min_amo23_12_1_,
partnerent1_.min_shipment as min_shi24_12_1_,
partnerent1_.min_sum_order as min_sum25_12_1_,
partnerent1_.own_delivery as own_del26_12_1_,
partnerent1_.own_production as own_pro27_12_1_,
partnerent1_.phones as phones28_12_1_,
partnerent1_.return_information as return_29_12_1_,
partnerent1_.site as site30_12_1_
from
product productent0_
inner join
partner partnerent1_
on productent0_.owner_id=partnerent1_.user_id
inner join
stock_product stocks2_
on productent0_.id=stocks2_.product_id
where
productent0_.id=?
group by
productent0_.id ,
partnerent1_.user_id
But it's not very convenient.
Why DTO projection doesn't work correctrly, but tuple works fine?

Because that's how Hibernate is currently implemented.
Because you used an entity in the DTO Projection, which as the name implies, it should be used for DTOs, not entities, Hibernate is going to assume that you want to GROUP BY by the identifier because it should not GROUP BY all entity properties.
The Tuple is broken and it will only work in MySQL, but not in Oracle or PostgreSQL since your aggregate query selects columns that are not present in the GROUP BY clause.
However, this is not demanded to work according to the JPA specs. Nevertheless, you should still provide a replicating test case and open an issue so that the behavior is the same for both situations.
Anyway, once fixed, it will still GROUP BY identifier. If you want to select entities and group by as well, you will have to use a native SQL query along with the Hibernate ResultTransformer to transform the ResultSet into a graph of objects.
More, fetching entities and aggregations is a code smell. Most likely, you need a DTO projection or a read-only view.
Entities should only be fetched when you want to modify them. Otherwise, a DTO projection is more efficient and more straightforward as well.

Since Vlad already explained the why, I will focus on an alternative solution. Having to specify all attributes that you are really interested in in the SELECT clause and the GROUP BY clause is a lot of work.
If you used Blaze-Persistence Entity Views on top of Hibernate, this could look like the following
#EntityView(ProductEntity.class)
public interface ProductCountDTO {
// Or map the ProductEntity itself if you like..
#Mapping("this")
ProductView getProduct();
#Mapping("sum(stocks.rest)")
int getCount();
}
#EntityView(ProductEntity.class)
public interface ProductView {
// Whatever mappings you like
}
With the Spring Data or DeltaSpike Data integration you can even use it like that
Optional<ProductCountDTO> findById(long id);
It will produce a JPQL query like the following
SELECT
p /* All the attributes you map in ProductView */,
sum(stocks_1.rest)
FROM
ProductEntity p
LEFT JOIN
p.stocks stocks_1
GROUP BY
p /* All the attributes you map in ProductView */
Maybe give it a shot? https://github.com/Blazebit/blaze-persistence#entity-view-usage
The magic is that Blaze-Persistence handles the GROUP BY automatically when encountering an aggregate function by putting every non-aggregate expression you use into the GROUP BY clause if there is at least one aggregate function used.
When using Entity Views instead of entities directly, you won't be facing the join fetch problems as Entity Views will only put the fields you actually map into the resulting SELECT clause of the JPQL and SQL.
Even if you used entities directly or via the ProductCountDTO, the query builder used behind the scenes handles selects of entity types in case of a group by gracefully, just as you'd expect it from Hibernate.

Hibernate: separate sql query for every collection

I have a Person class that has a collection of Contacts. Everything works ok, I get the list of persons with their contacts. However, in log I see that a separate query is made to read collection of every person. That is too bad.
How to make hibernate make a join to read all the data in one query? I use JPA.
This is the person class:
#Entity
#Table(name = "tbl1")
public class PersonItem implements Serializable{
#Id
#Column(name="col1")
private String guid;
.....
#ElementCollection(targetClass = ContactItem.class,fetch=FetchType.EAGER)
#CollectionTable(name="tbl2",joinColumns=#JoinColumn(name="col2"))
private List<ContactItem> contacts;
....
}
This is the contact class
#Embeddable
#Table(name = "tbl2")
public class ContactItem implements Serializable {
#Column(name="col1")
private String guid;
#Column(name="col3")
private String info;
}
This is the way I get the list of persons:
Query query = em.createQuery("Select p from PersonItem p WHERE p.guid IN (:guids)");
query.setParameter("guids", guids);
List<PersonItem> list=query.getResultList();
And this what I see in log (I have three persons in DB):
Hibernate: select personitem0_.col1 as col1_0_, personitem0_.col4 as col2_0_, personitem0_.col2 as col3_0_, personitem0_.col3 as col4_0_ from tbl1 personitem0_ where personitem0_.col1 in (? , ? , ?)
Hibernate: select contacts0_.col2 as col1_1_0_, contacts0_.col1 as col2_1_0_, contacts0_.col3 as col3_1_0_ from tbl2 contacts0_ where contacts0_.col2=?
Hibernate: select contacts0_.col2 as col1_1_0_, contacts0_.col1 as col2_1_0_, contacts0_.col3 as col3_1_0_ from tbl2 contacts0_ where contacts0_.col2=?
Hibernate: select contacts0_.col2 as col1_1_0_, contacts0_.col1 as col2_1_0_, contacts0_.col3 as col3_1_0_ from tbl2 contacts0_ where contacts0_.col2=?

Please, begin from a more simple mapping. Use plural names, and column prefixes.
#Entity
#Table(name = "persons")
public class Person {
#Id
#Column(name = "f_guid")
private String guid;
#OneToMany(mappedBy = "person", fetch = FetchType.EAGER)
private List<Contact> contacts;
}
#Entity
#Table(name = "contacts")
public class Contact {
#Id
#Column(name = "f_guid")
private String guid;
#Column(name = "f_info")
private String info;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "fk_person")
private Person person;
}
Person is associated to contacts by a foreign key fk_person in the contacts table.
Update
Looks like JPQL overrides a default fetching strategy. You need to specify a fetch explicitly
select p from PersonItem p left join fetch p.contacts WHERE p.guid IN (:guids)
If you have duplicates, cause of joins, you can use distinct
select distinct p from PersonItem p left join fetch p.contacts WHERE p.guid IN (:guids)

Try #Fetch on your relation.
Also i would suggest to use #OneToMany relation int this case
#OneToMany(mappedBy = "person", fetch = FetchType.EAGER)
#Fetch(FetchMode.JOIN) //You can use SUBSELECT as well
private List<ContactItem> contacts;
You can read more about fetching strategies here
fetch-“join” = Disable the lazy loading, always load all the collections and entities.
fetch-“select” (default) = Lazy load all the collections and entities.
batch-size=”N” = Fetching up to ‘N’ collections or entities, Not record.
fetch-“subselect” = Group its collection into a sub select statement.

How to make left join on two parameters in Ebean?

I have two tables: "users" and "mail_list" with corresponding classes.
These tables are connected with the help of foreign key user_id (in mail_list table) that references id (in users table). Users can have records of two kinds in mail_list table - 'general' or/and 'admin'. If user has a record in mail_list table, this means that he doesn't want to recieve mails of corresponding kind.
I'd like to find all users who want to recieve mails of general kind. I'm sure that the right SQL query looks like this:
SELECT U.id, U.email, M.user_id, M.kind
FROM users U
LEFT JOIN mail_list M
ON (U.id = M.user_id AND M.kind = 'general')
WHERE M.user_id IS NULL
But unfortunately I'm not so good with Ebean. Could you, please, help me to write such a Ebean query if it is possible? I'd like to avoid using Raw SQL.
Here, also, some code of my classes is:
#Entity
#Table(name = "users")
public class User {
#Id
public Long id;
public String email;
#OneToMany(mappedBy = "user")
public List<MailList> mailLists;
}
#Entity
#Table(name = "mail_list")
public class MailList {
#Id
public Long id;
/**
* Kind of mail list
*/
public String kind;
public static String GENERAL = "general";
public static String ADMIN = "admin";
#ManyToOne
public User user;
}
I use PlayFramework 2.2.3.

My solution to your problem is:
List<MailList> mailList = MailList.find.where().like("kind", "general").findList();
Set<User> userSet = new HashSet<User>();
for(MailList mail:mailList)
userSet.add(mail.user);
It finds mailing lists that fulfill search criteria. Then it creates set of users.

I think this is what you are looking for:
Finder<Long, User> finder = new Finder<Long, User>(Long.class, User.class);
List<User> users = finder.fetch("mailLists").where().eq("mailLists.kind", "general").findList();
This piace of code will generate the following query:
SELECT U.id, U.email, M.user_id, M.kind
FROM users U
LEFT JOIN mail_list M ON U.id = M.user_id
WHERE M.kind = 'general';
I suggest you to use enum instead of static strings. This will be better to reference on your source code.
The unique part that I didn't understood on your question is the part that you use a field to join a table but on the where you filter for null values of that field.

Define a variable in Entity class which is not a column

In my WAS application, I have a requirement to define a variable(String) in an Entity class that maps to a table.
So the fields that are related to the table have annotation as #Column(name="column_name")
I have a requirement to add a new field/variable to this Entity class that is not a column in table. If I declare it as a normal field, JPA converts this field also in the SQLs. This is causing SQL -206 error(as expected).
How to do I declare this field? Is there an annotation that I can use to say its a custom variable and not related to any of the columns in the table defined by this Entity?
example:
#Entity
#Table(name = "TABLE_1")
#NamedQueries(
{
#NamedQuery(name = "abc:findTableContent", query = "SELECT u FROM TABLE_1 u WHERE u.Id = :iD"),
})
public class TableEntity1 implements Serializable
{
#Id
#Column(name = "TABLE1_ID")
private Long iD;
#Column(name = "DESC")
private String desc;
private String error;
}
So if I run the namedquery, it gets executed as "SELECT t0.iD, t0.desc, t0.error FROM TABLE_1 u WHERE u.iD=?"
How do I solve this? Thanks for your help!

I found the answer. I could mark the field or variable as #javax.persistence.Transient