[hibernate-dev] [OGM] Id generation strategies

[Emmanuel Bernard]

On 24 Jun 2014, at 11:50, Gunnar Morling <gunnar at hibernate.org> wrote:

> Yes, today we don't.
> 
> But is there any reason for not using the value column name?

Not more that the ones I outlined in this thread.

> 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.

I don’t follow that one. A fixed schema would be fine here, just with two columns instead of one, no?

> 
> 
> 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.
> 
>