Respect metadata-defined facet ordering in sorted_facet_results (#2648)

* Preserve metadata-defined facet ordering on table pages

When facets are explicitly defined in table metadata/config, they now
appear in the order specified in the configuration rather than being
sorted by result count. Request-added facets still appear after
metadata-defined facets, sorted by count as before.

* Document metadata-defined facet ordering behavior

* Apply black formatting

https://claude.ai/code/session_01PbSHtjsUpNk3Fx7xjvVqDb

datasette/views/table.py

@@ -1580,11 +1580,35 @@ async def table_view_data(
         ]
 
     async def extra_sorted_facet_results(extra_facet_results):
-        return sorted(
-            extra_facet_results["results"].values(),
-            key=lambda f: (len(f["results"]), f["name"]),
-            reverse=True,
-        )
+        facet_configs = table_metadata.get("facets", [])
+        if facet_configs:
+            # Build ordered list of facet names from metadata config
+            metadata_facet_names = []
+            for fc in facet_configs:
+                if isinstance(fc, str):
+                    metadata_facet_names.append(fc)
+                elif isinstance(fc, dict):
+                    metadata_facet_names.append(list(fc.values())[0])
+            metadata_order = {name: i for i, name in enumerate(metadata_facet_names)}
+            metadata_facets = []
+            request_facets = []
+            for f in extra_facet_results["results"].values():
+                if f["name"] in metadata_order:
+                    metadata_facets.append(f)
+                else:
+                    request_facets.append(f)
+            metadata_facets.sort(key=lambda f: metadata_order[f["name"]])
+            request_facets.sort(
+                key=lambda f: (len(f["results"]), f["name"]),
+                reverse=True,
+            )
+            return metadata_facets + request_facets
+        else:
+            return sorted(
+                extra_facet_results["results"].values(),
+                key=lambda f: (len(f["results"]), f["name"]),
+                reverse=True,
+            )
 
     async def extra_table_definition():
         return await db.get_table_definition(table_name)

docs/facets.rst

@@ -153,6 +153,8 @@ Here's an example that turns on faceting by default for the ``qLegalStatus`` col
 
 Facets defined in this way will always be shown in the interface and returned in the API, regardless of the ``_facet`` arguments passed to the view.
 
+Facets defined in metadata will be displayed in the order they are listed in the configuration. Any additional facets added via query string parameters (e.g. ``?_facet=column_name``) will appear after the metadata-defined facets, sorted by the number of unique values.
+
 You can specify :ref:`array <facet_by_json_array>` or :ref:`date <facet_by_date>` facets in metadata using JSON objects with a single key of ``array`` or ``date`` and a value specifying the column, like this:
 
 .. [[[cog

tests/test_facets.py

@@ -623,12 +623,48 @@ def test_other_types_of_facet_in_metadata():
         }
     ) as client:
         response = client.get("/fixtures/facetable")
-        for fragment in (
-            "<strong>created (date)\n",
-            "<strong>tags (array)\n",
+        fragments = (
             "<strong>state\n",
-        ):
+            "<strong>tags (array)\n",
+            "<strong>created (date)\n",
+        )
+        for fragment in fragments:
             assert fragment in response.text
+        # Verify they appear in the metadata-defined order
+        positions = [response.text.index(f) for f in fragments]
+        assert positions == sorted(
+            positions
+        ), "Facets should appear in metadata-defined order"
+
+
+def test_metadata_facet_ordering():
+    with make_app_client(
+        metadata={
+            "databases": {
+                "fixtures": {
+                    "tables": {
+                        "facetable": {
+                            "facets": ["state", {"array": "tags"}, {"date": "created"}]
+                        }
+                    }
+                }
+            }
+        }
+    ) as client:
+        # JSON response should have facets in the metadata-defined order
+        response = client.get("/fixtures/facetable.json?_extra=sorted_facet_results")
+        data = response.json
+        facet_names = [f["name"] for f in data["sorted_facet_results"]]
+        assert facet_names == ["state", "tags", "created"]
+
+        # With an additional request-based facet, metadata facets come first
+        # in their defined order, followed by request-based facets
+        response2 = client.get(
+            "/fixtures/facetable.json?_extra=sorted_facet_results&_facet=_city_id"
+        )
+        data2 = response2.json
+        facet_names2 = [f["name"] for f in data2["sorted_facet_results"]]
+        assert facet_names2 == ["state", "tags", "created", "_city_id"]
 
 
 @pytest.mark.asyncio