I have a Company
entity that I fetch with a JPQL query with Hibernate. The entity has a many-to-many association with a Keyword
entity. Since the join table has an additional column is_active
, this table has been mapped to a CompanyKeyword
entity. So the association is like this:
Company <-- CompanyKeyword --> Keyword
Now, the association from the Company
entity is lazy, and it is not initialized by my JPQL query, as I want to avoid creating a cartesian product performance problem. That is why I want to initialize the association after running the JPQL query, eg like this:
@Service
class CompanyServiceImpl implements CompanyService {
@Autowired
private CompanyRepository companyRepository;
@Transactional
public Company findOne(int companyId) {
Company company = this.companyRepository.findOneWithSomeCustomQuery(companyId);
Hibernate.initialize(company.companyKeywords());
return company;
}
}
For a "normal" many-to-many association, this would work great, as all of the associated entities would be fetched in a single query. However, since I have an entity between Company
and Keyword
, Hibernate will only initialize the first part of the association , ie from Company
to CompanyKeyword
, and not from CompanyKeyword
to Keyword
. I hope that makes sense. I am looking for a way to initialize this association all the way without having to do something like this:
Company company = this.companyRepository.findOneWithSomeCustomQuery(companyId);
Hibernate.initialize(company.getCompanyKeywords());
for (CompanyKeyword ck : company.getCompanyKeywords()) {
Hibernate.initialize(ck.getKeyword());
}
The above code is neither clean, nor good in terms of performance. If possible, I would like to stick to my current approach of using a JPQL query to fetch my Company
entity and then initializing certain associations afterwards; it would take quite a bit of refactoring to change this in my project. Should I just "manually" fetch the association with a second JPQL query, or is there a better way of doing it that I haven't thought of?
Below are my mappings. Thanks in advance!
Company
@Entity
@Table(name = "company")
public class Company implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column
private int id;
@Size(max = 20)
@OneToMany(fetch = FetchType.LAZY, mappedBy = "company")
private Set<CompanyKeyword> companyKeywords = new HashSet<>();
// Getters and setters
}
CompanyKeyword
@Entity
@Table(name = "company_service")
@IdClass(CompanyServicePK.class)
public class CompanyKeyword implements Serializable {
@Id
@ManyToOne(fetch = FetchType.LAZY, targetEntity = Company.class)
@JoinColumn(name = "company_id")
private Company company;
@Id
@ManyToOne(fetch = FetchType.LAZY, targetEntity = Keyword.class)
@JoinColumn(name = "keyword_id")
private Keyword keyword;
@Column(nullable = true)
private boolean isActive;
// Getters and setters
}
CompanyKeywordPK
public class CompanyServicePK implements Serializable {
private Company company;
private Service service;
public CompanyServicePK() { }
public CompanyServicePK(Company company, Service service) {
this.company = company;
this.service = service;
}
// Getters and setters
// hashCode()
// equals()
}
Keyword
@Entity
@Table(name = "keyword")
public class Keyword {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column
private int id;
// Fields and getters/setters
}
You'll indeed need to execute an additional JPQL query, fetching the company with its companyKeyWords and with the keyword of each CompanyKeyWord.
You could also doing it by simply looping and initializing every entity, and still avoid executing too many queries, by enabling batch fetching .
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