Added a test

https://gistpreview.github.io/?4418a16a35c71ac1efdb3bd2bd74b580

datasette/renderer.py

@@ -108,7 +108,11 @@ 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"):
+    # Parse comma-separated _extra values
+    extras = set()
+    for bit in request.args.getlist("_extra"):
+        extras.update(bit.split(","))
+    if isinstance(data, dict) and "columns" not in extras:
         data.pop("columns", None)
 
     # Handle _nl option for _shape=array

datasette/views/extras.py

@@ -0,0 +1,185 @@
+"""
+Shared extras functionality for table and row views.
+"""
+
+from datasette.plugins import pm
+from datasette.resources import TableResource
+from datasette.utils import await_me_maybe
+
+
+def _get_extras(request):
+    """Parse ?_extra= parameters from request into a set of extra names."""
+    extra_bits = request.args.getlist("_extra")
+    extras = set()
+    for bit in extra_bits:
+        extras.update(bit.split(","))
+    return extras
+
+
+async def render_cells_for_rows(
+    datasette, database_name, table_name, rows, columns, request
+):
+    """
+    Call render_cell plugin hook for each cell.
+    Returns a list of dicts, one per row, containing only cells modified by plugins.
+    """
+    rendered_rows = []
+    for row in rows:
+        rendered_row = {}
+        for value, column in zip(row, columns):
+            plugin_display_value = None
+            for candidate in pm.hook.render_cell(
+                row=row,
+                value=value,
+                column=column,
+                table=table_name,
+                database=database_name,
+                datasette=datasette,
+                request=request,
+            ):
+                candidate = await await_me_maybe(candidate)
+                if candidate is not None:
+                    plugin_display_value = candidate
+                    break
+            if plugin_display_value:
+                rendered_row[column] = str(plugin_display_value)
+        rendered_rows.append(rendered_row)
+    return rendered_rows
+
+
+class SharedExtras:
+    """
+    Extras that are shared between table and row views.
+
+    Initialize with context, then call get_extras() to process requested extras.
+    Subclass to add view-specific extras.
+    """
+
+    # Extras that this class can provide
+    available_extras = {
+        "columns",
+        "primary_keys",
+        "database",
+        "table",
+        "database_color",
+        "query",
+        "render_cell",
+        "table_definition",
+        "view_definition",
+        "is_view",
+        "private",
+        "metadata",
+    }
+
+    def __init__(
+        self,
+        datasette,
+        db,
+        database_name,
+        table_name,
+        request,
+        rows,
+        columns,
+        pks,
+        sql=None,
+        params=None,
+    ):
+        self.datasette = datasette
+        self.db = db
+        self.database_name = database_name
+        self.table_name = table_name
+        self.request = request
+        self.rows = rows
+        self.columns = columns
+        self.pks = pks
+        self.sql = sql
+        self.params = params
+
+    async def get_extras(self, extras):
+        """
+        Process a set of extra names and return a dict of results.
+        Only processes extras that this class knows how to handle.
+        """
+        results = {}
+        for extra in extras:
+            method = getattr(self, f"extra_{extra}", None)
+            if method:
+                results[extra] = await method()
+        return results
+
+    async def extra_columns(self):
+        """Column names returned by this query"""
+        return self.columns
+
+    async def extra_primary_keys(self):
+        """Primary keys for this table"""
+        return self.pks
+
+    async def extra_database(self):
+        """Database name"""
+        return self.database_name
+
+    async def extra_table(self):
+        """Table name"""
+        return self.table_name
+
+    async def extra_database_color(self):
+        """Database color"""
+        return self.db.color
+
+    async def extra_query(self):
+        """Details of the underlying SQL query"""
+        return {
+            "sql": self.sql,
+            "params": self.params,
+        }
+
+    async def extra_render_cell(self):
+        """Rendered HTML for each cell using the render_cell plugin hook"""
+        return await render_cells_for_rows(
+            self.datasette,
+            self.database_name,
+            self.table_name,
+            self.rows,
+            self.columns,
+            self.request,
+        )
+
+    async def extra_table_definition(self):
+        """SQL schema for this table"""
+        return await self.db.get_table_definition(self.table_name)
+
+    async def extra_view_definition(self):
+        """SQL schema for this view (if it is a view)"""
+        return await self.db.get_view_definition(self.table_name)
+
+    async def extra_is_view(self):
+        """Is this a view rather than a table?"""
+        return await self.db.view_exists(self.table_name)
+
+    async def extra_private(self):
+        """Is this table private?"""
+        visible, _ = await self.datasette.check_visibility(
+            self.request.actor,
+            action="view-table",
+            resource=TableResource(database=self.database_name, table=self.table_name),
+        )
+        return not visible
+
+    async def extra_metadata(self):
+        """Metadata about the table and database"""
+        tablemetadata = await self.datasette.get_resource_metadata(
+            self.database_name, self.table_name
+        )
+        rows = await self.datasette.get_internal_database().execute(
+            """
+            SELECT column_name, value
+            FROM metadata_columns
+            WHERE database_name = ?
+              AND resource_name = ?
+              AND key = 'description'
+            """,
+            [self.database_name, self.table_name],
+        )
+        tablemetadata["columns"] = dict(rows)
+        return tablemetadata

datasette/views/row.py

@@ -12,7 +12,8 @@ from datasette.utils import (
 from datasette.plugins import pm
 import json
 import sqlite_utils
-from .table import display_columns_and_rows, _get_extras
+from .table import display_columns_and_rows
+from .extras import _get_extras, SharedExtras
 
 
 class RowView(DataView):
@@ -111,38 +112,28 @@ class RowView(DataView):
         if "foreign_key_tables" in (request.args.get("_extras") or "").split(","):
             extras.add("foreign_key_tables")
 
-        # Process extras
+        # Process shared extras using SharedExtras class
+        shared_extras = SharedExtras(
+            datasette=self.ds,
+            db=db,
+            database_name=database,
+            table_name=table,
+            request=request,
+            rows=rows,
+            columns=columns,
+            pks=resolved.pks,
+            sql=resolved.sql,
+            params=resolved.params,
+        )
+        extra_results = await shared_extras.get_extras(extras)
+        data.update(extra_results)
+
+        # Handle row-specific extras
         if "foreign_key_tables" in extras:
             data["foreign_key_tables"] = await self.foreign_key_tables(
                 database, table, pk_values
             )
 
-        if "render_cell" in extras:
-            # Call render_cell plugin hook for each cell
-            rendered_rows = []
-            for row in rows:
-                rendered_row = {}
-                for value, column in zip(row, columns):
-                    # Call render_cell plugin hook
-                    plugin_display_value = None
-                    for candidate in pm.hook.render_cell(
-                        row=row,
-                        value=value,
-                        column=column,
-                        table=table,
-                        database=database,
-                        datasette=self.ds,
-                        request=request,
-                    ):
-                        candidate = await await_me_maybe(candidate)
-                        if candidate is not None:
-                            plugin_display_value = candidate
-                            break
-                    if plugin_display_value:
-                        rendered_row[column] = str(plugin_display_value)
-                rendered_rows.append(rendered_row)
-            data["render_cell"] = rendered_rows
-
         return (
             data,
             template_data,

datasette/views/table.py

@@ -46,6 +46,7 @@ from datasette.filters import Filters
 import sqlite_utils
 from .base import BaseView, DatasetteError, _error, stream_csv
 from .database import QueryView
+from .extras import _get_extras, render_cells_for_rows
 
 LINK_WITH_LABEL = (
     '<a href="{base_url}{database}/{table}/{link_id}">{label}</a>&nbsp;<em>{id}</em>'
@@ -679,14 +680,6 @@ class TableDropView(BaseView):
         return Response.json({"ok": True}, status=200)
 
 
-def _get_extras(request):
-    extra_bits = request.args.getlist("_extra")
-    extras = set()
-    for bit in extra_bits:
-        extras.update(bit.split(","))
-    return extras
-
-
 async def _columns_to_select(table_columns, pks, request):
     columns = list(table_columns)
     if "_col" in request.args:
@@ -1495,29 +1488,9 @@ async def table_view_data(
     async def extra_render_cell():
         "Rendered HTML for each cell using the render_cell plugin hook"
         columns = [col[0] for col in results.description]
-        rendered_rows = []
-        for row in rows:
-            rendered_row = {}
-            for value, column in zip(row, columns):
-                # Call render_cell plugin hook
-                plugin_display_value = None
-                for candidate in pm.hook.render_cell(
-                    row=row,
-                    value=value,
-                    column=column,
-                    table=table_name,
-                    database=database_name,
-                    datasette=datasette,
-                    request=request,
-                ):
-                    candidate = await await_me_maybe(candidate)
-                    if candidate is not None:
-                        plugin_display_value = candidate
-                        break
-                if plugin_display_value:
-                    rendered_row[column] = str(plugin_display_value)
-            rendered_rows.append(rendered_row)
-        return rendered_rows
+        return await render_cells_for_rows(
+            datasette, database_name, table_name, rows, columns, request
+        )
 
     async def extra_query():
         "Details of the underlying SQL query"

tests/test_api.py

@@ -809,6 +809,48 @@ async def test_row_extra_render_cell():
         ds.pm.unregister(name="TestRenderCellPlugin")
 
 
+@pytest.mark.asyncio
+async def test_row_extras_shared():
+    """Test that shared extras (columns, query, metadata, etc.) work on row pages"""
+    from datasette.app import Datasette
+
+    ds = Datasette(memory=True)
+    await ds.invoke_startup()
+    db = ds.add_memory_database("test_row_extras")
+    await db.execute_write(
+        "create table test_extras (id integer primary key, name text, age integer)"
+    )
+    await db.execute_write("insert into test_extras values (1, 'Alice', 30)")
+
+    # Test multiple shared extras
+    response = await ds.client.get(
+        "/test_row_extras/test_extras/1.json"
+        "?_extra=columns,primary_keys,query,database,table,database_color"
+        ",table_definition,is_view,private,metadata"
+    )
+    assert response.status_code == 200
+    data = response.json()
+
+    # Verify shared extras are present and correct
+    assert data["columns"] == ["id", "name", "age"]
+    assert data["primary_keys"] == ["id"]
+    assert data["database"] == "test_row_extras"
+    assert data["table"] == "test_extras"
+    assert data["database_color"] is not None  # Has some color value
+    assert data["is_view"] is False
+    assert data["private"] is False
+    assert "columns" in data["metadata"]  # metadata has columns dict
+
+    # query extra should have sql and params
+    assert "sql" in data["query"]
+    assert "params" in data["query"]
+    assert "test_extras" in data["query"]["sql"]
+
+    # table_definition should be the CREATE TABLE statement
+    assert "CREATE TABLE" in data["table_definition"]
+    assert "test_extras" in data["table_definition"]
+
+
 def test_databases_json(app_client_two_attached_databases_one_immutable):
     response = app_client_two_attached_databases_one_immutable.get("/-/databases.json")
     databases = response.json