Improve support for relation table mapping to prevent redundancy

[zdila]

I'd like to generate 3 tables for rendering hiking (bicycle, ...) routes:

1. segments

   • way_id
   • geometry

2. routes

   • relation_id
   • name (from relation)
   • osmc:symbol (from relation)
   • network (from relation)
   • ref (from relation)

3. membership

   • way_id
   • relation_id

I found no way to map it with imposm3. There I can only create 2 tables:

• relation table which corresponds to my routes table
• relation_member table which corresponds to my segments table optionally joined with membership or even routes table

Reason why I need schema I described is that for every segment I want to do select like:

SELECT geometry, string_agg("osmc:symbol", '~') FROM segments NATURAL JOIN membership NATURAL JOIN routes GROUP BY way_id

I can work around this problem by only using these with two tables (of types relation_member and relation) but I don't like the geometry colum is redundantly multiplied in table of the relation_member.