JPA unidirectional ManyToMany - duplicated positions in when retrieving list

Question

I had following entities in my project:

AccountGroup
AccountItem
AccountSegment

With folowing relations:

AccountGroup has List<AccountItem>
AccountItem had List<AccountSegment>

and everything worked fine.

When I changed last relation to:

AccountItem has Set<AccountSegment>

AccountGroup object read from database looks strange. If given AccountItem had three AccountSegments, then I have three the same AccountItems in AccountGroup.

A shot from debugger can possibly tell it better than I can: SS from debugger

As you can see, accountMapperItems list has four positions instead of two. First pair is a duplicate each having the same variables. (second is similar, not shown on screenshot).

Below I paste entities code fragments:

class AccountGroup {
    ...
    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "group")
    private List<AccountItem> accountMapperItems;
    ....
}

class AccountItem {
    ...
    @ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.REFRESH, CascadeType.MERGE })
    @JoinTable(
        joinColumns={@JoinColumn(name="ACCOUNT_ITEM_ID", referencedColumnName="ID")},
        inverseJoinColumns={@JoinColumn(name="SEGMENT_ID", referencedColumnName="ID")})
    private Set<Segment> segmentSet;

    @ManyToOne
    private AccountGroup group;
    ...
}

AccountSegment does not have any links.

Does anyone know why is it retriving accountMapperItems list one position per AccountSegment?

The problem is not duplicate entries in jointable! I have double checked it.

Update

@Fetch (FetchMode.SELECT)

solved the case, further explanations are available in post mentioned in the answer.

score 3 · Accepted Answer · edited May 23 '17 at 12:22

3

Make sure all your entities implement hashCode() and equals(). These methods are used by some collections (like Sets) to uniquely identify elements.

Edit: If that doesn't solve it, then I think the duplicates are most likely caused by the FetchType.EAGER. This answer explains it well. Try removing the FetchType.EAGER to see if it makes any difference.

edited May 23 '17 at 12:22

Community

1
1

answered Feb 10 '14 at 16:16

David Levesque

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After adding equals and hashcode methods to both objects `AccountSegment` and `AccountItem` behaviour remains the same. Both methods are based only on primary key. – Maciej Dobrowolski Feb 10 '14 at 16:34
Are you retrieving data through JPQL queries, or are you just using the collections getters? – David Levesque Feb 10 '14 at 16:36
I am retrieving only `AccountGroup` using entity manager method `find(AcountGroup.class, id)` – Maciej Dobrowolski Feb 10 '14 at 16:38
Thanks! `@Fetch (FetchMode.SELECT)` from the link you gave solved the case! – Maciej Dobrowolski Feb 10 '14 at 19:51

JPA unidirectional ManyToMany - duplicated positions in when retrieving list

1 Answers1