> How does your original example of ManyToMany annotation on a Collection
> of Enums actually work? My understanding is that for ManyToMany both
> sides must be persistent Entities. So therefore the ManyToMany is
> mapping the join table, not the Enum.
yes oddly enough it actually does work. As per my subsequent email, I
switched it to @PersistentCollection and it performed the same way. I
considered trying to annotate my Enum like an Entity but I figured that
would be pushing expected behaviour... even if it worked, so I decided not
to.
> Isn't the same thing true that OneToMany should annotate a Collection of
> Entities? So the Enums would be a field on the ManyToOne side of that
> kind of mapping. Then you can specify the @Column and @Enumerated
> annotations on the actual field or property.
no you can't, I tried it. I can't remember the specific error but it was
along the lines of - you're not allowed to specify a column attribute
here.
> Could you explain why using the @PersistentCollection annotation is
> useful or necessary for OneToMany or ManyToMany collections generally or
> specifically in the case you are looking at? I don't understand the use
> case that @PersistentCollection satisfies.
My understanding is @ManyToMany is a JPA standard and is only used to map
entity to entities.
My understanding of @PersistentCollection is that is is an OpenJpa
extention which allows people to map Entity to java Primities.
i.e.
@Entity
class Bar
{
}
@Entity
class Foo
{
@ManyToMany
HashSet<Bar> myBars=new HashSet<Bar>();
@PersistentCollection
HashSet<String> myStrings=new HashSet<String>();
}
I guess there's a reason why the original JPA standard left out
primitives... it gets complicated fast.
> - Paul
>
>
> On 3/29/2009 8:43 PM, Tedman Leung wrote:
>> Just to document more thoughts and findings.
>>
>> 1) I was using the wrong annotation, I should have been using
>> @PersistentCollection
>>
>> 2) this seems to be a more wide spread problem with defining
>> attributes to collections, i.e. - collection of enums needs to have
>> @Enumerated configurations
>> - collection of Dates needs to have @Temporal configurations
>> - even collection of Strings seems to be missing a
>> @Column(nullable=false, length=32) style annotation.
>>
>> I think the problem is much bigger and wide spread than I originaly though,
>> I don't think I'll be able to sort out a patch.
>>
>>
>> On Sun, Mar 29, 2009 at 07:55:06AM -0700, Tedman Leung wrote:
>>
>>> yes I know I can do manual hacks to get them stored the way I want
>>> to, but I was asking if there was a jpa / openjpa annotation to allow
>>> that.
>>>
>>> As an example, I can just use @Enumerated on a single enum, so it
>>> seems logical that some one would have thought about storing a
>>> collection of enums.
>>>
>>> As for why I want them as strings instead of ordinals - the usual
>>> reasons, i.e. it's safer for changes as the ordering won't
>>> accidentally corrupt my data (and without telling me), and it's
>>> easier to look into the database via sql or something and just know
>>> what's going on / get simple reports etc.
>>>
>>> I'm guessing right now that it's not possible at all and that no one
>>> has done anything towards this. I might have to rummage through the
>>> source and try to see if I can figure out how it works and hack a
>>> patch to submit. It seemed like a very straight forward use case
>>> though so I'm surprised no one has asked or done anything about this
>>> before.
>>>
>>>
>>>
>>> On Sat, Mar 28, 2009 at 10:13:16PM -0700, Paul Copeland wrote:
>>>
>>>> What is your objective? Do you want some non-JPA application to
>>>> see them in the database as Strings?
>>>>
>>>> At some point you have add these Enums to the collection one at a
>>>> time. You can use an addEnum() method or an Entity listener to
>>>> convert them to Strings at that point one at a time. And a
>>>> subclass of the Collection type to getEnum() from the Collection
>>>> when you fetch them back.
>>>>
>>>> new MyStringEnumHashSet<MyStringEnumType>()
>>>>
>>>> On 3/28/2009 9:27 PM, Tedman Leung wrote:
>>>>
>>>>> No, I'm talking about when the enum is in a collection.
>>>>>
>>>>> i.e.
>>>>>
>>>>> Private HashSet<Gender> genders=new HashSet<Gender>();
>>>>>
>>>>> So no, either the @Enumerated helps, nor does calling name() or
>>>>> toString as neither are possible.
>>>>>
>>>>> I'm storing a Collection of enums , not a single Enum.
>>>>>
>>>>> There seems to be no examples of this nor any documentation about
>>>>> the ability to do this that I can find. The default seems to use
>>>>> the ordinal value both for table generation and storage value.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Sat, Mar 28, 2009 at 01:56:13PM -0700, Paul Copeland wrote:
>>>>>
>>>>>> Hi - This is from the OpenJPA relations example -
>>>>>>
>>>>>> @Basic @Enumerated(EnumType.STRING)
>>>>>> private Gender gender;
>>>>>>
>>>>>> public static enum Gender { MALE, FEMALE }
>>>>>>
>>>>>> public void setGender(Gender gender) {
>>>>>> this.gender = gender;
>>>>>> }
>>>>>>
>>>>>> See section 12.8.1.2 in the OpenJPA Overview
>>>>>>
>>>>>> - Paul
>>>>>>
>>>>>> On 3/28/2009 1:33 PM, catalina wei wrote:
>>>>>>
>>>>>>> Ted,
>>>>>>> If you are using Java 5, then you could use name() or toString() API on
>>>>>>> the
>>>>>>> Enum to get the name of the enum constant in String value.
>>>>>>>
>>>>>>> Catalina
>>>>>>>
>>>>>>> On Wed, Mar 25, 2009 at 9:48 AM, Tedman Leung <[email protected]> wrote:
>>>>>>>
>>>>>>>
>>>>>>>> Anyone know how to store a collection of enums as Strings instead of
>>>>>>>> their
>>>>>>>> ordinal values? (preferably with annotations...)
>>>>>>>>
>>>>>>>> i.e.
>>>>>>>> @ManyToMany
>>>>>>>> private Set<MyEnum> myEnums=new HashSet<MyEnum>();
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> Ted Leung
>>>>>>>> [email protected]
>>>>>>>>
>>>>>>>> It's time for a new bike when the bulb in your shift light burns out.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>
>>> --
>>> Ted Leung
>>> [email protected]
>>>
>>> The most important words I've learned to say - "I don't know".
>>>
>>
>>
>
--
Ted Leung
[email protected]
It's time for a new bike when the bulb in your shift light burns out.
