html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,issue,performed_via_github_app
https://github.com/simonw/sqlite-utils/issues/402#issuecomment-1032732242,https://api.github.com/repos/simonw/sqlite-utils/issues/402,1032732242,IC_kwDOCGYnMM49jj5S,25778,2022-02-08T15:26:59Z,2022-02-08T15:26:59Z,CONTRIBUTOR,"What if you did something like this:

```python

class Conversion:
    def __init__(self, *args, **kwargs):
        ""Put whatever settings you need here""

    def python(self, row, column, value): # not sure on args here
        ""Python step to transform value""
        return value

    def sql(self, row, column, value):
        ""Return the actual sql that goes in the insert/update step, and maybe params""
        # value is the return of self.python()
        return value, []
```

This way, you're always passing an instance, which has methods that do the conversion. (Or you're passing a SQL string, as you would now.) The `__init__` could take column names, or SRID, or whatever other setup state you need per row, but the row is getting processed with the `python` and `sql` methods (or whatever you want to call them). This is pretty rough, so do what you will with names and args and such.

You'd then use it like this:

```python
# subclass might be unneeded here, if methods are present
class LngLatConversion(Conversion):
    def __init__(self, x=""longitude"", y=""latitude""):
        self.x = x
        self.y = y

    def python(self, row, column, value):
        x = row[self.x]
        y = row[self.y]
        return x, y

    def sql(self, row, column, value):
        # value is now a tuple, returned above
        s = ""GeomFromText(POINT(? ?))""
        return s, value

table.insert_all(rows, conversions={""point"": LngLatConversion(""lng"", ""lat""))}
```

I haven't thought through all the implementation details here, and it'll probably break in ways I haven't foreseen, but wanted to get this idea out of my head. Hope it helps.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1125297737,
https://github.com/simonw/sqlite-utils/issues/402#issuecomment-1030904948,https://api.github.com/repos/simonw/sqlite-utils/issues/402,1030904948,IC_kwDOCGYnMM49clx0,9599,2022-02-06T20:09:42Z,2022-02-08T07:40:44Z,OWNER,"I think this is the code that needs to become aware of this system: https://github.com/simonw/sqlite-utils/blob/fea8c9bcc509bcae75e99ae8870f520103b9aa58/sqlite_utils/db.py#L2453-L2469

There's an earlier branch that runs for upserts which needs to be modified too: https://github.com/simonw/sqlite-utils/blob/fea8c9bcc509bcae75e99ae8870f520103b9aa58/sqlite_utils/db.py#L2417-L2440","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1125297737,
https://github.com/simonw/sqlite-utils/issues/402#issuecomment-1030902102,https://api.github.com/repos/simonw/sqlite-utils/issues/402,1030902102,IC_kwDOCGYnMM49clFW,9599,2022-02-06T19:53:34Z,2022-02-08T07:40:34Z,OWNER,"I like the idea that the contract for `Conversion` (or rather for its subclasses) is that it can wrap a Python value and then return both the SQL fragment - e.g. `GeomFromText(?, 4326)` - and the values that should be used as the SQL parameters.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1125297737,
https://github.com/simonw/sqlite-utils/issues/402#issuecomment-1032296717,https://api.github.com/repos/simonw/sqlite-utils/issues/402,1032296717,IC_kwDOCGYnMM49h5kN,9599,2022-02-08T07:35:46Z,2022-02-08T07:35:46Z,OWNER,"I'm going to write the documentation for this first, before the implementation, so I can see if it explains cleanly enough that the design appears to be sound.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1125297737,
https://github.com/simonw/sqlite-utils/issues/402#issuecomment-1032294365,https://api.github.com/repos/simonw/sqlite-utils/issues/402,1032294365,IC_kwDOCGYnMM49h4_d,9599,2022-02-08T07:32:09Z,2022-02-08T07:34:41Z,OWNER,"I have an idea for how that third option could work - the one that creates a new column using values from the existing ones:
```python
db[""places""].insert(
    {
        ""name"": ""London"",
        ""lng"": -0.118092,
        ""lat"": 51.509865,
    },
    conversions={""point"": LongitudeLatitude(""lng"", ""lat"")},
)
```
How about specifying that the values in that `conversion=` dictionary can be:

- A SQL string fragment (as currently implemented)
- A subclass of `Conversion` as described above
- Or... a callable function that takes the row as an argument and returns either a `Conversion` subclass instance or a literal value to be jnserted into the database (a string, int or float)

Then you could do this:

```python
db[""places""].insert(
    {
        ""name"": ""London"",
        ""lng"": -0.118092,
        ""lat"": 51.509865,
    },
    conversions={
        ""point"": lambda row: LongitudeLatitude(
            row[""lng""], row[""lat""]
        )
    }
)
```
Something I really like about this is that it expands the abilities of `conversions=` beyond the slightly obscure need to customize the SQL fragment into something that can solve other data insertion cleanup problems too.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",1125297737,