[hibernate-dev] RE: Exposing legacy Lucene documents on searches.

[Emmanuel Bernard]

This is correct, but Christian had a very interesting idea.
We could reuse the projection API to project the Lucene specific objects

fullTextQuery.setProjection("id", "title", "price",  
FullTextQuery.DOCUMENT, FullTextQuery.SCORE).list();

Would return a list of
Object[] {
   1, //the id
   "Au bonheur des dames", //title
   5.5, //price
   org.apache.lucene.document.Document at 123334, //"the raw Lucene doc"
   .556, //the Lucene Score for the given document
}

The benefits being :
  - a reductions of specific APIs (score, hits)
  - an easy navigation (everything (objects and Lucene objects  
accessible from the same array and API)


On Jun 18, 2007, at 4:15 AM, Hardy Ferentschik wrote:

> Hi John,
>
>> By the way could you please explain your 'projection' to me. I don't
>> understand the concept.
>
> The idea behind projections is to avoid full database round-trips  
> in uses cases where you are only interested in a subset of object  
> properties  (instead of the full Hibernate managed object). Lucene  
> allows you to store the original values of the fields you are  
> indexing in the index itself. This functioanlity is exposed in  
> HSearch via the annotation @Field(store=Store.YES).
>
> My favourite use case is a online shop. Normally such a site has  
> some sort of search functionality. Say that only the title, price  
> and category of an item is searchable and beeing displayed on the  
> search result page. If you store these properties in the lucene  
> index you can retrieve them at search time and just return these  
> 'projected' values without accessing the database. When a user then  
> clicks on a single item you would normally retrieve the fully  
> managed Item object from the database (probably using the hibernate  
> id)
>
> Projections will be returned as object arrays. Have a look at the  
> example in the HSearch documentation:
> http://www.hibernate.org/hib_docs/search/reference/en/html_single/ 
> #d0e1139
>
> Cheers
> Hardy