java - Spring Data JPARepository: How to conditionally fetch children entites

Question

How can one configure their JPA Entities to not fetch related entities unless a certain execution parameter is provided.

According to Spring's documentation, 4.3.9. Configuring Fetch- and LoadGraphs, you need to use the @EntityGraph annotation to specify fetch policy for queries, however this doesn't let me decide at runtime whether I want to load those entities.

I'm okay with getting the child entities in a separate query, but in order to do that I would need to configure my repository or entities to not retrieve any children. Unfortunately, I cannot seem to find any strategies on how to do this. FetchPolicy is ignored, and EntityGraph is only helpful when specifying which entities I want to eagerly retrieve.

For example, assume Account is the parent and Contact is the child, and an Account can have many Contacts.

I want to be able to do this:

if(fetchPolicy.contains("contacts")){
  account.setContacts(contactRepository.findByAccountId(account.getAccountId());
}

The problem is spring-data eagerly fetches the contacts anyways.

The Account Entity class looks like this:

@Entity
@Table(name = "accounts")
public class Account
{
    protected String accountId;
    protected Collection<Contact> contacts;

    @OneToMany
    //@OneToMany(fetch=FetchType.LAZY) --> doesn't work, Spring Repositories ignore this
    @JoinColumn(name="account_id", referencedColumnName="account_id")
    public Collection<Contact> getContacts()
    {
        return contacts;
    }

    //getters & setters

}

The AccountRepository class looks like this:

public interface AccountRepository extends JpaRepository<Account, String>
{
    //@EntityGraph ... <-- has type= LOAD or FETCH, but neither can help me prevent retrieval
    Account findOne(String id);
}

Answer 1

The lazy fetch should be working properly if no methods of object resulted from the getContacts() is called.

If you prefer more manual work, and really want to have control over this (maybe more contexts depending on the use case). I would suggest you to remove contacts from the account entity, and maps the account in the contacts instead. One way to tell hibernate to ignore that field is to map it using the @Transient annotation.

@Entity
@Table(name = "accounts")
public class Account
{
    protected String accountId;
    protected Collection<Contact> contacts;

    @Transient
    public Collection<Contact> getContacts()
    {
        return contacts;
    }

    //getters & setters

}

Then in your service class, you could do something like:

public Account getAccountById(int accountId, Set<String> fetchPolicy) {
    Account account = accountRepository.findOne(accountId);
    if(fetchPolicy.contains("contacts")){
        account.setContacts(contactRepository.findByAccountId(account.getAccountId());
    }
    return account;
}

Hope this is what you are looking for. Btw, the code is untested, so you should probably check again.