Berkano

Add equals(), hashCode() and toString() methods in classes that are persisted

Details

  • Type: Improvement Improvement
  • Status: Open Open
  • Priority: Major Major
  • Resolution: Unresolved
  • Affects Version/s: None
  • Fix Version/s: None
  • Component/s: user
  • Labels:
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  • Number of attachments :
    0

Description

This is just an improvement of classes to be persisted because Hibernate relies on these methods to work correctly.
Didn't say that this is mandatory but could probably help in some situations.

Activity

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Grégory Joseph added a comment -

Well, the thing with these methods and hibernate, is that in some cases you would have to implement them in a "non standard" way. (ie in java, you would usually compare all fields in the equals method, while with hibernate in mind, you would maybe only compare the pk field)

So please describe where/how this would help, with what kind of implementation. I'm not against this at all, but I've never had the time to understand, sit and think about the whole issue, which is why it's as it is at the moment.

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Grégory Joseph added a comment - Well, the thing with these methods and hibernate, is that in some cases you would have to implement them in a "non standard" way. (ie in java, you would usually compare all fields in the equals method, while with hibernate in mind, you would maybe only compare the pk field) So please describe where/how this would help, with what kind of implementation. I'm not against this at all, but I've never had the time to understand, sit and think about the whole issue, which is why it's as it is at the moment.
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Frederic Burlet added a comment -

My test case is the following (code does not compile but give an idea of the scenario).

Collection<User> allUsersFromSomeGroups = new HashSet<User>;
User u = UserDAO.getUserById(id);
Collection<Group> groups = user.getGroups();
for(Group g: groups) {
allUsersFromSomeGoup.addAll(g.getUsers());
}
allUsersFromSomeGroup.contains(oneSpecificUser); // returns false and if you go deep through the collection you can see that the "oneSpecificUser" is there.
I'm probably missing something... anyway... already the toString() method will be help full...

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Frederic Burlet added a comment - My test case is the following (code does not compile but give an idea of the scenario). Collection<User> allUsersFromSomeGroups = new HashSet<User>; User u = UserDAO.getUserById(id); Collection<Group> groups = user.getGroups(); for(Group g: groups) { allUsersFromSomeGoup.addAll(g.getUsers()); } allUsersFromSomeGroup.contains(oneSpecificUser); // returns false and if you go deep through the collection you can see that the "oneSpecificUser" is there. I'm probably missing something... anyway... already the toString() method will be help full...
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Grégory Joseph added a comment -

oh, yes, this makes perfect sense of course
Now the "fun" part will be to decide how to implement the equals and hashcode methods, as I've never found a clear guide.. In the book I had, they basically explained both solutions but didn't give (or i didn't understand) a clear guideline as to decide which one to use...

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Grégory Joseph added a comment - oh, yes, this makes perfect sense of course Now the "fun" part will be to decide how to implement the equals and hashcode methods, as I've never found a clear guide.. In the book I had, they basically explained both solutions but didn't give (or i didn't understand) a clear guideline as to decide which one to use...

People

  • Assignee:
    Grégory Joseph
    Reporter:
    Frederic Burlet
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  • Created:
    Updated: