These don't appear to be Arrow Datetime values, but rather some custom/extension type called google:sqlType:datetime, and we do not have support in Polars for arbitrary Arrow extension types. I'd hope it's possible to return standard Arrow Datetime types from BigQuery, but not sure if I currently have access to an instance to check/verify that 🤔

I can confirm this issue is still present in polars 1.20.0. When trying to handle BigQuery's google:sqlType:datetime type, Polars does not properly convert it to standard Arrow Datetime values.

Steps to reproduce:

1. Query BigQuery table containing datetime fields
2. Attempt to load results into Polars dataframe
3. Observe that datetime fields retain the custom google:sqlType:datetime type instead of converting to Arrow Datetime

The specific error encountered is:

ComputeError: cannot create series from Extension(ExtensionType { name: "google:sqlType:datetime", inner: Timestamp(Microsecond, None), metadata: None })

I can confirm this issue is still present in polars 1.20.0. When trying to handle BigQuery's google:sqlType:datetime type, Polars does not properly convert it to standard Arrow Datetime values.

Indeed - but then, we shouldn't have to; ideally BigQuery should be able to produce standard Arrow Datetime values rather than a custom "google:sqlType:datetime" ExtensionType (I'm unsure why they do this 🤔).

Removing the metadata from the fields seems to work as a workaround:

table = job.to_arrow()
table = pa.Table.from_batches(table.to_batches(), schema=pa.schema([field.remove_metadata() for field in table.schema]))
df = pl.from_arrow(table)

Any idea why it worked in polars<1.18.0? Here's some sample data in case someone wants to investigate: https://storage.googleapis.com/cosmic-mariner-294413-ew6/table.parquet

>>> table = pq.read_table('table.parquet')
>>> table.schema
record_id: int64
date_of_occurence: timestamp[us]
  -- field metadata --
  ARROW:extension:name: 'google:sqlType:datetime'
>>> table.field(1).type
TimestampType(timestamp[us])
>>> table.field(1).metadata
{b'ARROW:extension:name': b'google:sqlType:datetime'}