table extension Column is not JSON serializable

[martinfleis]

When trying to use the table extension, I think I hit a bug (or I don't know how to use it). See the example:

from datetime import datetime

import pystac
from pystac.extensions.table import TableExtension, Column

catalog = pystac.Catalog(
    id="test_catalog",
    description="Test catalog",
    )

# create Item
item = pystac.Item(id='countries',
                 geometry=None,
                 bbox=[0, 1, 1, 2],
                 datetime=datetime.utcnow(),
                 href="./data.json",
                 properties={},
                 )

# add column metadata
tab_ext = TableExtension.ext(item, add_if_missing=True)
tab_ext.columns = [
    Column({"name": 'col_1', "type": 'str'}),
    Column({"name": 'col_2', "type": 'byte_array'}),
]

# add asset
item.add_asset(
    key='data',
    asset=pystac.Asset(
        title="Dataset root",
        href="./data.parquet",
        media_type="application/x-parquet"
    )
)

# add to collection
catalog.add_item(item)

catalog.normalize_hrefs("stac/")
catalog.save(catalog_type=pystac.CatalogType.SELF_CONTAINED)

The last line raises

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Untitled-1.ipynb Cell 4 in <cell line: 1>()
----> 1 catalog.save(catalog_type=pystac.CatalogType.SELF_CONTAINED)

...

TypeError: Object of type Column is not JSON serializable

I believe that this mirrors the issue #605 and change I made on this branch (main...martinfleis:pystac:table_serialize) fixes it. Happy to turn it into a PR if that is an actual bug and not my misunderstanding of the API.

[m-mohr]

I'm running into the same issue... I just don't use the TableExtension for now.