[hibernate-dev] [OGM] Id generation strategies

[Emmanuel Bernard]

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.