[hibernate-dev] Hibernate Search Projection

[Emmanuel Bernard]

>
>> Projection
>> The ability to project some fields the index only avoiding the
>> database roundtrip.
>> fullTextQuery.setProjection("id", "summary", "author.name").list();
>> will return a List<Object[]> like the regular HQL projection
>> the fieldbridge has to be two way (all built-in are) and the
>> projected fields have to be Store.YES or Store.COMPRESS
>
> Looks good to me. It is a shame so that you have to specify the  
> index field names explicitly as strings.
> I wonder if there could be another way? On the one hand you are  
> able to index a field just via annoation,
> not caring what the lucene field name will be, on the other hand  
> you have to use the field names in the projection.
> Unfortunately, I haven't used projections before so I have to  
> understand the code first.
> My main question right now - what type of objects are returned from  
> the query? Partly populated objects of the
> managed classes or some other sort of objects?
> Nevertheless, I will try it right away. I was basically looking for  
> a solution which would not go all the way to the
> database.

What is retrieved is an Object[], it's a true projection, like a HQL  
one, I will add the resultTransformer feature later on though, so the  
Object[] can be converted.

You assume that someone will want to retrieve all the stored fields  
and that HSearch can guess the list of fields. But it may very well  
be a subset of the stored fields depending on the query, hence the  
actual list of fields. Then if I return an Object[], with all fields,  
the question of the ordering pops up.

My idea was to keep it consistent with what users do today in Hibernate.


>
>> A few questions:
>> Currently fields Store.NO or where the fieldbridge is one way are
>> ignored and return null.
>> The idea behind that is to be able to project across multiple
>> entities / index. Not sure if it's a useful feature.
> I guess I would expect an error if I include a field to be  
> projected, but it is not stored in the index.

OK I will change that

>
>
>> Expose resultSize()
>> ie the total number of result regardless of the pagination
>> fullTextQuery.setMaxResult(20)resultSize() == 3000
>> A better name is more than welcome.
> I would also opt for getResultSize()

OK