6:35 a.m.
Hi,
For the sake of completeness, here is the mapping obtained with Morphia:
{ "_id" : ObjectId("5784ca2612d0226cb309666d"), "className"
:
"TestEntity", "embeddeds" : [ { "singleProperty" :
"value1" }, {
"singleProperty" : "value2" } ], "embedded" : {
"singleProperty" :
"value" }, "collectionOfStrings" : [ "string1",
"string2" ] }
They are basically following the POLA and follow the Java mapping for
the MongoDB one.
Btw, to be complete, here are the reasons why I would like to change
it (I agree we have to maintain compatibility with older databases
but, as Sanne, I think it should be the new default):
1/ POLA: I would expect my datastore mapping to follow my Java mapping
2/ related to 1/: I wouldn't expect to have to migrate my data when I
simply add a property to an existing embeddable
3/ remove special cases in our code, especially special cases present
in the dialects
4/ I don't think we are completely consistent with this behavior.
Typically, if I take StoryGame from our tests and remove all the
properties but one from OptionalStoryBranch, I end up with the
following:
- in the datastore: "chaoticBranches" : [ "[VENDETTA] assassinate the
leader of the party", "[ARTIFACT] Search for the evil artifact" ] -
this is what we expect, only one property, we remove the property
level
- in the native query generated by our JPA query "FROM StoryGame story
JOIN story.chaoticBranches c WHERE c.evilText = '[ARTIFACT] Search for
the evil artifact'": where={ "chaoticBranches.evilText" :
"[ARTIFACT]
Search for the evil artifact"}
-> so our JPQL queries don't work if we only have one property in the
embedded. We might also want to special case this but I really don't
think it's a good idea.
While this discussion might seem to come out of the blue, it's in fact
related to OGM-893 and another special casing we do. See my comment
here:
https://hibernate.atlassian.net/browse/OGM-893?focusedCommentId=79245&...
. The mapping is changing when we add a @Column with a name for a
property of an embedded in a collection element.
--
Guillaume
On Tue, Jul 12, 2016 at 12:18 PM, Sanne Grinovero <sanne(a)hibernate.org> wrote:
On 12 July 2016 at 11:13, Gunnar Morling <gunnar(a)hibernate.org>
wrote:
>> I'd be concerned about schema evolution:
>
> Yes, that's the main argument; as said, I can see that.
>
>> I'd see more value in making this the default, and have an "higher
>> level" configuration property which is like "read like OGM 5.0 used to
>> store it".
>
> I wouldn't like changing such default in a 5.x release. For 6, ok, why not,
> if you all think that's better.
ok
>
>> Even better, we'd provide tooling which migrates an existing database.
>
> Sure, migration support is on the roadmap ;)
>
>
>
>
>
> 2016-07-12 11:06 GMT+01:00 Sanne Grinovero <sanne(a)hibernate.org>:
>>
>> On 12 July 2016 at 10:55, Gunnar Morling <gunnar(a)hibernate.org> wrote:
>> > Hi,
>> >
>> > We had an interesting discussion on how to map element collections of
>> > component types with a single column to document stores such as MongoDB.
>> >
>> > E.g. assume we have
>> >
>> > @Entity
>> > public class Person {
>> >
>> > public String name;
>> >
>> > @ElementCollection
>> > public List<Status> statusHistory;
>> > }
>> >
>> > @Embeddable
>> > public class Status {
>> > public String name;
>> > }
>> >
>> >
>> > Currently, that's mapped to documents like this:
>> >
>> > {
>> > "name" : "Bob";
>> > "statusHistory" : [
>> > "great",
>> > "mediocre",
>> > "splendid"
>> > ]
>> > }
>>
>> "great", "mediocre", etc.. are values of the `name`
property?
>>
>> >
>> > I.e. if the component type has a single column, we omit the field name
>> > in
>> > the persistent structure. Whereas if there are multiple columns, it's
>> > added
>> > so we can properly read back such documents:
>> >
>> >
>> > {
>> > "name" : "Bob";
>> > "statusHistory" : [
>> > { "name" : "great", "date" :
"22.06.2016" },
>> > { "name" : "mediocre", "date" :
"15.05.2016" },
>> > { "name" : "splendid", "date" :
"12.04.2016" }
>> > ]
>> > }
>> >
>> > The question now is, should we also create such array of sub-documents,
>> > each containing the field name, in the case where there only is a single
>> > column. As far as I remember, the current structure has been chosen for
>> > the
>> > sake of efficiency but also simplicity (why deal with sub-documents if
>> > there only is a single field?).
>> >
>> > Guillaume is questioning the sanity of that, arguing that mapping this
>> > as
>> > an element collection of a component type rather than string should
>> > mandate
>> > the persistent structure to always contain the field name.
>>
>> I agree, but maybe for other reasons.
>> I'd be concerned about schema evolution: if I add a new attribute to
>> the `Status` class, say a "long timestampOfChance" for the sake of the
>> example,
>> as a developer I might want to consider this a nullable value as I'm
>> aware that my existing database didn't define this property so far.
>>
>> I wouldn't be happy to see failures on loading existing stored values
>> for Status#name : such mapping choices have to be very consistent.
>>
>> >
>> > We cannot change the default as we are committed to the MongoDB format,
>> > but
>> > if there is agreement that it's useful, we could add an option to
enable
>> > this mapping.
>>
>> So many mapping options :-/
>>
>> I'd see more value in making this the default, and have an "higher
>> level" configuration property which is like "read like OGM 5.0 used to
>> store it".
>> Even better, we'd provide tooling which migrates an existing database.
>>
>> >
>> > I kind of see how this format simplifies migration (in case another
>> > field
>> > is added after a while), but personally I still like the more compact
>> > looks
>> > of the current approach. Having an option for it works for me.
>> >
>> > Any thoughts?
>> >
>> > --Gunnar
>> > _______________________________________________
>> > hibernate-dev mailing list
>> > hibernate-dev(a)lists.jboss.org
>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
>
>
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