New ds.metadata() method

datasette/app.py

@@ -131,7 +131,7 @@ class Datasette:
         self.cache_headers = cache_headers
         self.cors = cors
         self._inspect = inspect_data
-        self.metadata = metadata or {}
+        self._metadata = metadata or {}
         self.sqlite_functions = []
         self.sqlite_extensions = sqlite_extensions or []
         self.template_dir = template_dir
@@ -167,6 +167,38 @@ class Datasette:
             for option in CONFIG_OPTIONS
         }
 
+    def metadata(self, key=None, database=None, table=None, fallback=True):
+        """
+        Looks up metadata, cascading backwards from specified level.
+        Returns None if metadata value is not foundself.
+        """
+        assert not (database is None and table is not None), \
+            "Cannot call metadata() with table= specified but not database="
+        databases = self._metadata.get("databases") or {}
+        search_list = []
+        if database is not None:
+            search_list.append(databases.get(database) or {})
+        if table is not None:
+            table_metadata = (
+                (databases.get(database) or {}).get("tables") or {}
+            ).get(table) or {}
+            search_list.insert(0, table_metadata)
+        search_list.append(self._metadata)
+        if not fallback:
+            # No fallback allowed, so just use the first one in the list
+            search_list = search_list[:1]
+        if key is not None:
+            for item in search_list:
+                if key in item:
+                    return item[key]
+            return None
+        else:
+            # Return the merged list
+            m = {}
+            for item in search_list:
+                m.update(item)
+            return m
+
     def app_css_hash(self):
         if not hasattr(self, "_app_css_hash"):
             self._app_css_hash = hashlib.sha1(
@@ -181,19 +213,19 @@ class Datasette:
         return self._app_css_hash
 
     def get_canned_queries(self, database_name):
-        names = self.metadata.get("databases", {}).get(database_name, {}).get(
+        queries = self.metadata(
-            "queries", {}
+            "queries", database=database_name, fallback=False
-        ).keys()
+        ) or {}
+        names = queries.keys()
         return [
             self.get_canned_query(database_name, name) for name in names
         ]
 
     def get_canned_query(self, database_name, query_name):
-        query = self.metadata.get("databases", {}).get(database_name, {}).get(
+        queries = self.metadata(
-            "queries", {}
+            "queries", database=database_name, fallback=False
-        ).get(
+        ) or {}
-            query_name
+        query = queries.get(query_name)
-        )
         if query:
             if not isinstance(query, dict):
                 query = {"sql": query}
@@ -220,7 +252,7 @@ class Datasette:
         seen_urls = set()
         for url_or_dict in itertools.chain(
             itertools.chain.from_iterable(getattr(pm.hook, key)()),
-            (self.metadata.get(key) or [])
+            (self.metadata(key) or [])
         ):
             if isinstance(url_or_dict, dict):
                 url = url_or_dict["url"]
@@ -246,12 +278,12 @@ class Datasette:
         # Fills in source/license with defaults, if available
         metadata.update(
             {
-                "source": metadata.get("source") or self.metadata.get("source"),
+                "source": metadata.get("source") or self.metadata("source"),
                 "source_url": metadata.get("source_url")
-                or self.metadata.get("source_url"),
+                or self.metadata("source_url"),
-                "license": metadata.get("license") or self.metadata.get("license"),
+                "license": metadata.get("license") or self.metadata("license"),
                 "license_url": metadata.get("license_url")
-                or self.metadata.get("license_url"),
+                or self.metadata("license_url"),
             }
         )
 
@@ -291,7 +323,7 @@ class Datasette:
                         "hash": inspect_hash(path),
                         "file": str(path),
                         "views": inspect_views(conn),
-                        "tables": inspect_tables(conn, self.metadata.get("databases", {}).get(name, {}))
+                        "tables": inspect_tables(conn, (self.metadata("databases") or {}).get(name, {}))
                     }
             except sqlite3.OperationalError as e:
                 if (e.args[0] == 'no such module: VirtualSpatialIndex'):
@@ -306,7 +338,7 @@ class Datasette:
 
     def register_custom_units(self):
         "Register any custom units defined in the metadata.json with Pint"
-        for unit in self.metadata.get("custom_units", []):
+        for unit in self.metadata("custom_units") or []:
             ureg.define(unit)
 
     def versions(self):
@@ -469,7 +501,7 @@ class Datasette:
             "/-/inspect<as_format:(\.json)?$>",
         )
         app.add_route(
-            JsonDataView.as_view(self, "metadata.json", lambda: self.metadata),
+            JsonDataView.as_view(self, "metadata.json", lambda: self._metadata),
             "/-/metadata<as_format:(\.json)?$>",
         )
         app.add_route(

datasette/views/base.py

@@ -74,7 +74,7 @@ class BaseView(RenderMixin):
 
     def table_metadata(self, database, table):
         "Fetch table-specific metadata."
-        return self.ds.metadata.get("databases", {}).get(database, {}).get(
+        return (self.ds.metadata("databases") or {}).get(database, {}).get(
             "tables", {}
         ).get(
             table, {}
@@ -314,7 +314,7 @@ class BaseView(RenderMixin):
         end = time.time()
         data["query_ms"] = (end - start) * 1000
         for key in ("source", "source_url", "license", "license_url"):
-            value = self.ds.metadata.get(key)
+            value = self.ds.metadata(key)
             if value:
                 data[key] = value
         if _format in ("json", "jsono"):

datasette/views/database.py

@@ -18,7 +18,7 @@ class DatabaseView(BaseView):
             return await self.custom_sql(request, name, hash, sql, _size=_size)
 
         info = self.ds.inspect()[name]
-        metadata = self.ds.metadata.get("databases", {}).get(name, {})
+        metadata = (self.ds.metadata("databases") or {}).get(name, {})
         self.ds.update_with_inherited_metadata(metadata)
         tables = list(info["tables"].values())
         tables.sort(key=lambda t: (t["hidden"], t["name"]))

datasette/views/index.py

@@ -49,7 +49,7 @@ class IndexView(RenderMixin):
             return self.render(
                 ["index.html"],
                 databases=databases,
-                metadata=self.ds.metadata,
+                metadata=self.ds.metadata(),
                 datasette_version=__version__,
                 extra_css_urls=self.ds.extra_css_urls(),
                 extra_js_urls=self.ds.extra_js_urls(),

datasette/views/table.py

@@ -737,7 +737,7 @@ class TableView(RowTableShared):
                 link_column=not is_view,
                 truncate_cells=self.ds.config("truncate_cells_html"),
             )
-            metadata = self.ds.metadata.get("databases", {}).get(name, {}).get(
+            metadata = (self.ds.metadata("databases") or {}).get(name, {}).get(
                 "tables", {}
             ).get(
                 table, {}
@@ -860,7 +860,9 @@ class RowView(RowTableShared):
                     ),
                     "_rows_and_columns.html",
                 ],
-                "metadata": self.ds.metadata.get("databases", {}).get(name, {}).get(
+                "metadata": (
+                    self.ds.metadata("databases") or {}
+                ).get(name, {}).get(
                     "tables", {}
                 ).get(
                     table, {}