From 847f3e0c92b5ac17200b2090bedcc5443bb08e4b Mon Sep 17 00:00:00 2001
From: Simon Willison <simonw@eventbrite.com>
Date: Mon, 13 Nov 2017 13:10:55 -0800
Subject: [PATCH] Implemented offset/limit pagination for views

Closes #70
---
 datasette/app.py  | 28 +++++++++++++++++++++-------
 tests/test_app.py | 21 ++++++++++++++++-----
 2 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/datasette/app.py b/datasette/app.py
index e94c7442..31e48137 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -382,8 +382,12 @@ class TableView(BaseView):
             params = {}
 
         next = special_args.get('_next')
+        offset = ''
         if next:
-            if use_rowid:
+            if is_view:
+                # _next is an offset
+                offset = ' offset {}'.format(int(next))
+            elif use_rowid:
                 where_clauses.append(
                     'rowid > :p{}'.format(
                         len(params),
@@ -410,8 +414,13 @@ class TableView(BaseView):
         if order_by:
             order_by = 'order by {} '.format(order_by)
 
-        sql = 'select {} from {} {}{}limit {}'.format(
-            select, escape_sqlite_table_name(table), where_clause, order_by, self.page_size + 1,
+        sql = 'select {select} from {table_name} {where}{order_by}limit {limit}{offset}'.format(
+            select=select,
+            table_name=escape_sqlite_table_name(table),
+            where=where_clause,
+            order_by=order_by,
+            limit=self.page_size + 1,
+            offset=offset,
         )
 
         rows, truncated, description = await self.execute(name, sql, params, truncate=True)
@@ -423,11 +432,16 @@ class TableView(BaseView):
         rows = list(rows)
         info = self.ds.inspect()
         table_rows = info[name]['tables'].get(table)
-        next = None
+        next_value = None
         next_url = None
         if len(rows) > self.page_size:
-            next = path_from_row_pks(rows[-2], pks, use_rowid)
-            next_url = urllib.parse.urljoin(request.url, path_with_added_args(request, {'_next': next}))
+            if is_view:
+                next_value = int(next or 0) + self.page_size
+            else:
+                next_value = path_from_row_pks(rows[-2], pks, use_rowid)
+            next_url = urllib.parse.urljoin(request.url, path_with_added_args(request, {
+                '_next': next_value,
+            }))
         return {
             'database': name,
             'table': table,
@@ -443,7 +457,7 @@ class TableView(BaseView):
                 'sql': sql,
                 'params': params,
             },
-            'next': next,
+            'next': next_value and str(next_value) or None,
             'next_url': next_url,
         }, lambda: {
             'database_hash': hash,
diff --git a/tests/test_app.py b/tests/test_app.py
index ad5b9386..cf803d47 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -122,8 +122,11 @@ def test_table_with_slashes_in_name(app_client):
     }]
 
 
-def test_paginate(app_client):
-    path = '/test_tables/no_primary_key.jsono'
+@pytest.mark.parametrize('path,expected_rows,expected_pages', [
+    ('/test_tables/no_primary_key.jsono', 201, 5),
+    ('/test_tables/paginated_view.jsono', 201, 5),
+])
+def test_paginate_tables_and_views(app_client, path, expected_rows, expected_pages):
     fetched = []
     count = 0
     while path:
@@ -132,9 +135,11 @@ def test_paginate(app_client):
         fetched.extend(response.json['rows'])
         path = response.json['next_url']
         if path:
-            assert path.endswith(response.json['next'])
-    assert 201 == len(fetched)
-    assert 5 == count
+            assert response.json['next'] and path.endswith(response.json['next'])
+        assert count < 10, 'Possible infinite loop detected'
+
+    assert expected_rows == len(fetched)
+    assert expected_pages == count
 
 
 def test_max_returned_rows(app_client):
@@ -190,6 +195,12 @@ WITH RECURSIVE
   )
   INSERT INTO no_primary_key SELECT * from cnt;
 
+CREATE VIEW paginated_view AS
+    SELECT
+        content,
+        '- ' || content || ' -' AS content_extra
+    FROM no_primary_key;
+
 CREATE TABLE "Table With Space In Name" (
   pk varchar(30) primary key,
   content text