Nsryjdtyk

The problem which i am trying to solve is avoid duplicate items inside a list attribute in hibernate.
Consider the below domain.

public class Account

    {

        @OneToMany(fetch = FetchType.LAZY)

        @JoinTable(name = "FI_COMPANY_ACCOUNT", joinColumns = @JoinColumn(name = "ACCOUNT_ID", referencedColumnName = "ID"), inverseJoinColumns = @JoinColumn(name = "COMPANY_ID", referencedColumnName = "ID"))

        private List<Company> companies;



        @OneToMany(fetch = FetchType.LAZY, mappedBy = "account", cascade = CascadeType.ALL, orphanRemoval = true)

        private List<AccountDesc> accountDescList;

    }



public class Company {}



public class AccountDesc

{

    @ManyToOne(fetch = FetchType.LAZY)

    @JoinColumn(name = "PARENT_ID", referencedColumnName = "ID")

    private Account account;

}

I use a Criteria API to fetch Account. In the query i perform fetch using left join for companies and inner join for accountDescList attribute. This help me to get both attributes in first select, and which avoid further selects.

Root<Account> root = criteriaQuery.from(Account.class);

root.fetch("companies", JoinType.LEFT);

root.fetch("accountDescList");

I know the root entity (here Account) can be repeated in the results. I can solve the issue using multiple ways like,
http://in.relation.to/2016/08/04/introducing-distinct-pass-through-query-hint/
https://howtoprogramwithjava.com/how-to-fix-duplicate-data-from-hibernate-queries/

But issue i face is the attribute companies inside the Account has also duplicate entities. This happen if we have more than one entry for accountDescList.

To solve the issue of duplicates in the attribute companies, I feel only solution is to use Set. Could you please clarify on the below questions.

1. Is there a way other than using Set (for the attribute companies), to solve this issue.


2. Even if i use can i instruct hibernate to use OrderedSetType (which uses LinkedHashSet). So that i can retain the order of the items as it returned from database. Unfortunately I do not have a attribute to use in OrderBy. I need the whatever default order returned by database.

Thanks in advance.

I think that it is much better use Set because a set doesn't allow elements duplicated, also you can overwrite equals method of Company and put it on what fields will be validated when two elements are equals.
The other way would be in setCompanies(List companies) method you can make something logic before this.companies = companies.stream().distinct().collect(Collectors.toList()); or
this.companies = new ArrayList<>(new HashSet(companies)) ;

But the issue I face is the attribute companies inside the Account has also duplicate entities.

That shouldn't happen unless you have duplicate Company entities assigned to the same account.

As explained in this article, using DISTINCT in the Criteria API query will remove root duplicates. However, in your case, it's not worth using JOIN FETCH on both @OneToMany relations since this will cause a Cartesian Product.

You should fetch at most one collection at a time, and maybe use @Subselect fetching for the second collection.