Hibernate 6 subquery number of relations.
org.springframework.dao.InvalidDataAccessResourceUsageException: Error interpreting query [SqmRoot not yet resolved to TableGroup]
What is the correct way of querying the number of related items with Criteria API?
I want to get back the below DTO, I have a OneToMany relation, I am interested about the number of related items.
I could not figure it out with AI, it might be a bug.
Example code: DTO:
package com.example.demo.dto;
import lombok.AllArgsConstructor;
import lombok.Data;
@Data
@AllArgsConstructor
public class Dto {
private Long id;
private Long count;
}
Entities:
package com.example.demo.entity;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.OneToMany;
import lombok.Data;
import java.util.Set;
import static jakarta.persistence.GenerationType.IDENTITY;
@Data
@Entity
public class One {
@Id
@GeneratedValue(strategy = IDENTITY)
private Long id;
@OneToMany(mappedBy = "one")
private Set<Many> many;
}
package com.example.demo.entity;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.Id;
import jakarta.persistence.ManyToOne;
import lombok.Data;
import static jakarta.persistence.FetchType.LAZY;
import static jakarta.persistence.GenerationType.IDENTITY;
@Data
@Entity
public class Many {
@Id
@GeneratedValue(strategy = IDENTITY)
private Long id;
@ManyToOne(fetch = LAZY, optional = false)
private One one;
}
Repository:
package com.example.demo.repository;
import com.example.demo.dto.Dto;
import com.example.demo.entity.Many;
import com.example.demo.entity.One;
import jakarta.persistence.EntityManager;
import jakarta.persistence.criteria.CriteriaBuilder;
import jakarta.persistence.criteria.CriteriaQuery;
import jakarta.persistence.criteria.Root;
import jakarta.persistence.criteria.Subquery;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Repository;
import java.util.List;
@Repository
@RequiredArgsConstructor
public class OneRepositoryCustom {
private final EntityManager entityManager;
public List<Dto> query() {
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Dto> cq = cb.createQuery(Dto.class);
Root<One> root = cq.from(One.class);
Subquery<Long> countMany = cq.subquery(Long.class);
Root<One> correlatedRoot = countMany.correlate(root);
Root<Many> manyRoot = countMany.from(Many.class);
countMany.select(cb.count(manyRoot));
countMany.where(cb.equal(manyRoot.get("one"), correlatedRoot));
cq.select(cb.construct(Dto.class, root.get("id"), countMany.getSelection()));
return entityManager.createQuery(cq).getResultList();
}
}
POM.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>4.0.1</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>25</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<annotationProcessorPaths>
<path>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</path>
</annotationProcessorPaths>
</configuration>
</plugin>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
</project>