table facet_size in metadata, refs #1804

datasette/facets.py

@@ -102,11 +102,19 @@ class Facet:
     def get_facet_size(self):
         facet_size = self.ds.setting("default_facet_size")
         max_returned_rows = self.ds.setting("max_returned_rows")
+        table_facet_size = None
+        if self.table:
+            tables_metadata = self.ds.metadata("tables", database=self.database) or {}
+            table_metadata = tables_metadata.get(self.table) or {}
+            if table_metadata:
+                table_facet_size = table_metadata.get("facet_size")
         custom_facet_size = self.request.args.get("_facet_size")
-        if custom_facet_size == "max":
-            facet_size = max_returned_rows
-        elif custom_facet_size and custom_facet_size.isdigit():
+        if custom_facet_size and custom_facet_size.isdigit():
             facet_size = int(custom_facet_size)
+        elif table_facet_size:
+            facet_size = table_facet_size
+        if facet_size == "max":
+            facet_size = max_returned_rows
         return min(facet_size, max_returned_rows)
 
     async def suggest(self):

tests/test_facets.py

@@ -581,6 +581,23 @@ async def test_facet_size():
     )
     data5 = response5.json()
     assert len(data5["facet_results"]["city"]["results"]) == 20
+    # Now try messing with facet_size in the table metadata
+    ds._metadata_local = {
+        "databases": {
+            "test_facet_size": {"tables": {"neighbourhoods": {"facet_size": 6}}}
+        }
+    }
+    response6 = await ds.client.get("/test_facet_size/neighbourhoods.json?_facet=city")
+    data6 = response6.json()
+    assert len(data6["facet_results"]["city"]["results"]) == 6
+    # Setting it to max bumps it up to 50 again
+    ds._metadata_local["databases"]["test_facet_size"]["tables"]["neighbourhoods"][
+        "facet_size"
+    ] = "max"
+    data7 = (
+        await ds.client.get("/test_facet_size/neighbourhoods.json?_facet=city")
+    ).json()
+    assert len(data7["facet_results"]["city"]["results"]) == 20
 
 
 def test_other_types_of_facet_in_metadata():