How can accent can be more accurate with bf and query with solr

i work with solr, i can't fix my problem of result's accuracy (q vs bf taking into account accents)

i have a solr index with 2 fields indexed (this is simplified):

town, population
Félines, 100
Ferrand, 10000

when i query: q=Fé&qf=town town_ascii&bf=population^2&defType=dismax I'd like this order on my results : Félines > Ferrand.

When i query: q=Fe&qf=town town_ascii&bf=population^2&defType=dismax I'd like this order on my results : Ferrand > Félines

The trouble is that Ferrand beats every time Félines because its population is bigger, how can i solve that? I didn't find how to use the score of the query and use it in bf to balance population

Solution

You didn't post your schema.xml but I suppose you're using the ASCIIFoldingFilterFactory for the town_ascii field. It means that if you're indexing the word Félines the following are the indexed terms:

town: Félines
town_ascii: Felines

Therefore, you're saying that a match for the town field is more important than a match for town_ascii. You should change the qf parameter to something like qf=town^3 town_ascii to give more weight to the town field. Then you can adjust the weight depending on what is the desired weight for town compared to population.