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https://issues.apache.org/jira/browse/COLLECTIONS-250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12492649
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Nikhil G. Daddikar commented on COLLECTIONS-250:
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It's not changed, my mistake.
Just as in a regular map that containsKey(key) is not equivalent to
getValue(key) != null, i.e. after doing a put(key, null), containsKey(key),
still returns true, I am expecting something similar. I find it wierd that
after doing a putAll(key, LIST), containsKey(key) returns FALSE, it should
return an empty list.
My problem is this (maybe this is not to be discussed here, but I think it is
appropriate at least to put the problem forward): I use MultiHashMap (MHM) for
caching database results of 1-to-many relationships. Let's say its is a PERSON
borrowed BOOKS relation. So, I do one SQL query to fetch all the books for many
(not all) persons and then populate the MHM cache (SELECT book_id from
BorrowedBooks where person_id in (id1, id2, id3...)). After populating, the MHM
has person1->books borrowed by person1, person2->books borrwed by person2 etc.
Now, a query comes asking for books borrowed by personX. Since there is no way
of asking the MHM whether "this key has no entries", if I don't find the
personX's key in the MHM, it is unclear if the caching query had fetched
personX's id in the original query. If there was a way, of maintaining empty
collections in the MHM, then this problem can be solved.
Also there is no way to put an empty list for a key which I could have used as
workaround.
> containsKey on MultiHashMap seems incorrect
> -------------------------------------------
>
> Key: COLLECTIONS-250
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-250
> Project: Commons Collections
> Issue Type: Bug
> Components: Map
> Affects Versions: 3.1, 3.2
> Reporter: Nikhil G. Daddikar
> Priority: Critical
>
> MultiHashMap m = new MultiHashMap();
> m.putAll("key", Collections.EMPTY_LIST);
> System.out.println(m.containsKey("key"))
> It says false, when it should have printed true.
> The problem is that the code in MultiHashMap and even MultiValueMap has in
> putAll():
> if (values == null || values.size() == 0)
> {
> return false;
> }
> This means that they key is never being entered into the Map. This is causing
> a huge problem because the behaviour has changed.
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