This happens only when both :include and a sub-query with a reference to the host table exist.

The queries from the console:

SHOW FIELDS FROM places

SHOW FIELDS FROM tags

SELECT places.id AS t0_r0, places.name AS t0_r1, (all tbl fields here) tags.id AS t1_r0, tags.name AS t1_r1, (all tags fields here) FROM places LEFT OUTER JOIN places_tags ON places_tags.place_id = places.id LEFT OUTER JOIN tags ON tags.id = places_tags.tag_id WHERE ((select count() from places_tags r where places.id=r.place_id)>0)
ORDER BY case when latitude>0 and longitude>0 then 0 else 1 end, (ACOS(least(1,COS(0.607053980163728)COS(0.559636997218594)COS(RADIANS(places.latitude))COS(RADIANS(places.longitude))+
COS(0.607053980163728)SIN(0.559636997218594)COS(RADIANS(places.latitude))SIN(RADIANS(places.longitude))+ SIN(0.607053980163728)SIN(RADIANS(places.latitude))))*6376.77271)

This is the sub-query with the reference:
select count(*) from places_tags r where places.id=r.place_id

when I remove either the :include or the sub-query condition, it works (the distance expression is in the select list). I need that condition so now I have 1+N queries which is bad performance.

Because GeoKit::GeoLoc has a hash method that returns a hash instead of the expected Fixnum, it is not always possible to serialize these objects. (See: http://apidock.com/ruby/Object/hash)

It would be preferable if the methods that return hashes are called to_h, or to_hash, or perhaps both, as is convention.

This is easily demonstrated as:

GeoKit::Geocoders::MultiGeocoder.geocode('123 main st.').all.to_yaml
# => TypeError: can't convert Hash into Integer