WIP table_filter plugin hook

datasette/hookspecs.py

@@ -33,3 +33,8 @@ def publish_subcommand(publish):
 @hookspec(firstresult=True)
 def render_cell(value):
     "Customize rendering of HTML table cell values"
+
+
+@hookspec
+def table_filter():
+    "Custom filtering of the current table based on the request"

datasette/utils.py

@@ -1,5 +1,5 @@
 from contextlib import contextmanager
-from collections import OrderedDict
+from collections import OrderedDict, namedtuple
 import base64
 import click
 import hashlib
@@ -39,6 +39,10 @@
 ENV SQLITE_EXTENSIONS /usr/lib/x86_64-linux-gnu/mod_spatialite.so
 '''
 
+TableFilter = namedtuple("TableFilter", (
+    "human_description_extras", "where_clauses", "params")
+)
+
 
 class InterruptedError(Exception):
     pass

datasette/views/table.py

@@ -313,7 +313,7 @@ async def data(self, request, name, hash, table, default_labels=False,  _next=No
         search_args = dict(
             pair for pair in special_args.items() if pair[0].startswith("_search")
         )
-        search_descriptions = []
+        human_description_extras = []
         search = ""
         if fts_table and search_args:
             if "_search" in search_args:
@@ -324,7 +324,7 @@ async def data(self, request, name, hash, table, default_labels=False,  _next=No
                         fts_table=escape_sqlite(fts_table),
                     )
                 )
-                search_descriptions.append('search matches "{}"'.format(search))
+                human_description_extras.append('search matches "{}"'.format(search))
                 params["search"] = search
             else:
                 # More complex: search against specific columns
@@ -341,13 +341,22 @@ async def data(self, request, name, hash, table, default_labels=False,  _next=No
                             i=i
                         )
                     )
-                    search_descriptions.append(
+                    human_description_extras.append(
                         'search column "{}" matches "{}"'.format(
                             search_col, search_text
                         )
                     )
                     params["search_{}".format(i)] = search_text
 
+        # filter_arguments plugin hook support
+        for awaitable_fn in pm.hook.table_filter():
+            extras = await awaitable_fn(
+                view=self, name=name, table=table, request=request
+            )
+            human_description_extras.extend(extras.human_description_extras)
+            where_clauses.extend(extras.where_clauses)
+            params.update(extras.params)
+
         table_rows_count = None
         sortable_columns = set()
         if not is_view:
@@ -713,7 +722,7 @@ async def data(self, request, name, hash, table, default_labels=False,  _next=No
                         pass
 
         # human_description_en combines filters AND search, if provided
-        human_description_en = filters.human_description_en(extra=search_descriptions)
+        human_description_en = filters.human_description_en(extra=human_description_extras)
 
         if sort or sort_desc:
             sorted_by = "sorted by {}{}".format(

docs/plugins.rst

@@ -320,3 +320,28 @@ If the value matches that pattern, the plugin returns an HTML link element:
             href=jinja2.escape(data["href"]),
             label=jinja2.escape(data["label"] or "") or " "
         ))
+
+table_filter
+~~~~~~~~~~~~
+
+Apply additional SQL filters to the current table based on the request.
+
+This should return an awaitable function with the following signature:
+
+.. code-block:: python
+
+    from datasette.utils import TableFilter
+
+    @hookimpl
+    def table_filter():
+        async def inner(view, name, table, request):
+            extra_human_descriptions = []
+            where_clauses = []
+            params = {}
+            # ... build those things here
+            return TableFilter(
+                human_description_extras=extra_human_descriptions,
+                where_clauses=where_clauses,
+                params=params,
+            )
+        return inner