id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,pull_request,body,repo,type,active_lock_reason,performed_via_github_app,reactions,draft,state_reason
1125297737,I_kwDOCGYnMM5DEq5J,402,Advanced class-based `conversions=` mechanism,9599,open,0,,,14,2022-02-06T19:47:41Z,2022-02-16T10:18:55Z,,OWNER,,"The `conversions=` parameter works like this at the moment: https://sqlite-utils.datasette.io/en/3.23/python-api.html#converting-column-values-using-sql-functions

```python
db[""places""].insert(
    {""name"": ""Wales"", ""geometry"": wkt},
    conversions={""geometry"": ""GeomFromText(?, 4326)""},
)
```
This proposal is to support values in that dictionary that are objects, not strings, which can represent more complex conversions - spun out from #399.

New proposed mechanism:
```python
from sqlite_utils.utils import LongitudeLatitude

db[""places""].insert(
    {
        ""name"": ""London"",
        ""point"": (-0.118092, 51.509865)
    },
    conversions={""point"": LongitudeLatitude},
)
```
Here `LongitudeLatitude` is a magical value which does TWO things: it sets up the `GeomFromText(?, 4326)` SQL function, and it handles converting the `(51.509865, -0.118092)` tuple into a `POINT({} {})` string.

This would involve a change to the `conversions=` contract - where it usually expects a SQL string fragment, but it can also take an object which combines that SQL string fragment with a Python conversion function.

Best of all... this resolves the `lat, lon` v.s. `lon, lat` dilemma because you can use `from sqlite_utils.utils import LongitudeLatitude` OR `from sqlite_utils.utils import LatitudeLongitude` depending on which you prefer!

_Originally posted by @simonw in https://github.com/simonw/sqlite-utils/issues/399#issuecomment-1030739566_",140912432,issue,,,"{""url"": ""https://api.github.com/repos/simonw/sqlite-utils/issues/402/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,