sphinx index with many-to-many relation

Question

I am trying to set up a Sphinx index with a basic many-to-many relation between artworks and genres:

artworks
---------------
id
title
description

genres
---------------
id
name

artwork_genres
---------------
artworks_id
genres_id

In my sphinx config file I have something like

source src_artwork {
    ...
    sql_query    = SELECT id, title, description FROM artworks
    sql_attr_multi = uint tag from query; SELECT id,name FROM genres
}

This is from the docs, as far as I can understand, on multi-valued attributes and sql_attr_multi

But obviously there is no mention of the tie table in there and I can't understand how that is brought into the config. I'd simply like for a search on "Impressionism" to result in artworks belonging to that genre (weighted as appropriate if the term is seen in the other fields)

Answer 1

I would consider ignoring the attributes feature in this case. The simplest way to create a genre field by which to search artworks is to "de-normalise" the genres table into the sql_query.

In the FROM clause of your SQL query, you would JOIN the genres table to the artworks via the linking table. In the SELECT clause, you can then GROUP_CONCAT genres.name into a column, which becomes a Sphinx field to search on.

Your sql_query might look like this:

source src_artwork {
        ...
    sql_query    = SELECT a.id, a.title, a.description, GROUP_CONCAT( DISTINCT g.name SEPARATOR ' ') AS genre \
        FROM artworks AS a \
        LEFT JOIN artwork_genres AS ag ON ag.artworks_id = a.id \ 
        LEFT JOIN genres AS g ON g.id = ag.genres_id
        GROUP BY a.id;
}

Then a sphinx search for artworks looking for "impressionism" in the @genre field will return the "row".