Centralize JSON extra parsing

datasette/extras.py

@@ -0,0 +1,6 @@
+def extra_names_from_request(request):
+    extra_bits = request.args.getlist("_extra")
+    extras = set()
+    for bit in extra_bits:
+        extras.update(part for part in bit.split(",") if part)
+    return extras

datasette/renderer.py

@@ -1,4 +1,5 @@
 import json
+from datasette.extras import extra_names_from_request
 from datasette.utils import (
     value_as_boolean,
     remove_infinites,
@@ -108,7 +109,7 @@ def json_renderer(request, args, data, error, truncated=None):
 
     # Don't include "columns" in output
     # https://github.com/simonw/datasette/issues/2136
-    if isinstance(data, dict) and "columns" not in request.args.getlist("_extra"):
+    if isinstance(data, dict) and "columns" not in extra_names_from_request(request):
         data.pop("columns", None)
 
     # Handle _nl option for _shape=array

datasette/views/table.py

@@ -6,6 +6,7 @@ import urllib
 from asyncinject import Registry
 import markupsafe
 
+from datasette.extras import extra_names_from_request
 from datasette.plugins import pm
 from datasette.database import QueryInterrupted
 from datasette.events import (
@@ -850,11 +851,7 @@ class TableDropView(BaseView):
 
 
 def _get_extras(request):
-    extra_bits = request.args.getlist("_extra")
-    extras = set()
-    for bit in extra_bits:
-        extras.update(bit.split(","))
-    return extras
+    return extra_names_from_request(request)
 
 
 async def _columns_to_select(table_columns, pks, request):

tests/test_table_api.py

@@ -1376,6 +1376,17 @@ async def test_table_extras(ds_client, extra, expected_json):
     assert response.json() == expected_json
 
 
+@pytest.mark.asyncio
+async def test_table_extra_columns_can_be_comma_separated(ds_client):
+    response = await ds_client.get(
+        "/fixtures/primary_key_multiple_columns.json?_extra=columns,count"
+    )
+    assert response.status_code == 200
+    data = response.json()
+    assert data["columns"] == ["id", "content", "content2"]
+    assert data["count"] == 1
+
+
 @pytest.mark.asyncio
 async def test_extra_render_cell():
     """Test that _extra=render_cell returns rendered HTML from render_cell plugin hook"""