[hibernate-dev] [OGM] Id generation strategies

[Gunnar Morling]

Yes, today we don't.

But is there any reason for not using the value column name? In fact that's
what my pending PR https://github.com/hibernate/hibernate-ogm/pull/337 does
for MongoDB. Right now it even allows to work with different value column
names for the same table (either in the same or in different
documents/records) but I plan to add a check disallowing this for the sake
of portability to stores with a fixed schema.


2014-06-20 13:00 GMT+02:00 Emmanuel Bernard <emmanuel at hibernate.org>:

>
> On 19 Jun 2014, at 14:54, Gunnar Morling <gunnar at hibernate.org> wrote:
>
> valueColumnName is something that I elected no to use because NoSQL we
>>> bind to so far do not have a strong schema. And at at given
>>> segmentColumnValue only correspond a single value. It would come and bite
>>> me if someone for the same segment value had two different value column
>>> names to differentiate two different sequence.
>>
>>
>> Would it really bite you? I think e.g. MongoDB could perfectly handle
>> this case via two different fields for the two sequences in the same
>> document/segment.
>>
>>
>> @TableGenerator(
>> name=“1”,
>> table=“Seq_table”,
>> pkColumnName=“key”,
>>  pkColumnValue=“1”,
>> valueColumnName=“value1”
>> )
>> @TableGenerator(
>> name=“2”,
>>  table=“Seq_table”,
>> pkColumnName=“key”,
>> pkColumnValue=“1”,
>>  valueColumnName=“value2”
>> )
>>
>> The two definitions share the same options except for valueColumnName.
>> The table is roughly as followed
>>
>> TABLE(Seq_table)
>> key    |    value1   |   value2
>> 1        |   10           |  24
>>
>> What would be the MongoDB representation in your approach?
>>
>
> It would look like this:
>
>     {
>         "_id" : 1,
>         "value1" : 10,
>         "value2" : 24
>     }
>
> So you would get the different sequence values from different fields of
> that same document. But I wouldn't recommend to do so due to the potential
> contention on that single record. Thus I'd raise at least a warning during
> bootstrap. As it's not portable to stores with a fixed schema, I'd rather
> not support it at all, though, and raise an error.
>
>
> Exactly. But that’s the thing, AFAIK we do *not* store it that way today
> as we don’t use valueColumnName. So today we store it like this
>
> {
>    “_id”: 1,
>    “sequence_value”: 10
> }
>
> so 10 and 24 has to both live at the same time in sequence _value.
>
>