Implemented cursor-based pagination for table view

Closes #5

datasette/app.py

@@ -14,10 +14,11 @@ import json
 import hashlib
 import time
 from .utils import (
-    build_where_clause,
+    build_where_clauses,
     CustomJSONEncoder,
     InvalidSql,
     path_from_row_pks,
+    path_with_added_args,
     compound_pks_from_path,
     sqlite_timelimit,
     validate_sql_select,
@@ -78,6 +79,7 @@ class BaseView(HTTPMethodView):
         self.files = datasette.files
         self.jinja = datasette.jinja
         self.executor = datasette.executor
+        self.page_size = datasette.page_size
         self.cache_headers = datasette.cache_headers
 
     def redirect(self, request, path):
@@ -270,16 +272,52 @@ class TableView(BaseView):
             select = '*'
             order_by = ', '.join(pks)
 
-        if request.args:
-            where_clause, params = build_where_clause(request.args)
-            sql = 'select {} from "{}" where {} order by {} limit 50'.format(
-                select, table, where_clause, order_by
-            )
+        # Special args start with _ and do not contain a __
+        # That's so if there is a column that starts with _
+        # it can still be queried using ?_col__exact=blah
+        special_args = {}
+        other_args = {}
+        for key, value in request.args.items():
+            if key.startswith('_') and '__' not in key:
+                special_args[key] = value[0]
+            else:
+                other_args[key] = value[0]
+
+        if other_args:
+            where_clauses, params = build_where_clauses(other_args)
         else:
-            sql = 'select {} from "{}" order by {} limit 50'.format(
-                select, table, order_by
-            )
-            params = []
+            where_clauses = []
+            params = {}
+
+        after = special_args.get('_after')
+        if after:
+            if use_rowid:
+                where_clauses.append(
+                    'rowid > :p{}'.format(
+                        len(params),
+                    )
+                )
+                params['p{}'.format(len(params))] = after
+            else:
+                pk_values = compound_pks_from_path(after)
+                if len(pk_values) == len(pks):
+                    param_counter = len(params)
+                    for pk, value in zip(pks, pk_values):
+                        where_clauses.append(
+                            '"{}" > :p{}'.format(
+                                pk, param_counter,
+                            )
+                        )
+                        params['p{}'.format(param_counter)] = value
+                        param_counter += 1
+
+        where_clause = ''
+        if where_clauses:
+            where_clause = 'where {}'.format(' and '.join(where_clauses))
+
+        sql = 'select {} from "{}" {} order by {} limit {}'.format(
+            select, table, where_clause, order_by, self.page_size + 1,
+        )
 
         rows = await self.execute(name, sql, params)
 
@@ -290,20 +328,27 @@ class TableView(BaseView):
         rows = list(rows)
         info = ensure_build_metadata(self.files)
         total_rows = info[name]['tables'].get(table)
+        after = None
+        after_link = None
+        if len(rows) > self.page_size:
+            after = path_from_row_pks(rows[-2], pks, use_rowid)
+            after_link = path_with_added_args(request, {'_after': after})
         return {
             'database': name,
             'table': table,
-            'rows': rows,
+            'rows': rows[:self.page_size],
             'total_rows': total_rows,
             'columns': columns,
             'primary_keys': pks,
             'sql': sql,
             'sql_params': params,
+            'after': after,
         }, lambda: {
             'database_hash': hash,
             'use_rowid': use_rowid,
             'row_link': lambda row: path_from_row_pks(row, pks, use_rowid),
             'display_columns': display_columns,
+            'after_link': after_link,
         }
 
 
@@ -381,13 +426,14 @@ def resolve_db_name(files, db_name, **kwargs):
 
 
 class Datasette:
-    def __init__(self, files, num_threads=3, cache_headers=True):
+    def __init__(self, files, num_threads=3, cache_headers=True, page_size=50):
         self.files = files
         self.num_threads = num_threads
         self.executor = futures.ThreadPoolExecutor(
             max_workers=num_threads
         )
         self.cache_headers = cache_headers
+        self.page_size = page_size
 
     def app(self):
         app = Sanic(__name__)

datasette/templates/table.html

@@ -34,5 +34,8 @@ td {
         </tr>
     {% endfor %}
 </table>
+{% if after_link %}
+    <p><a href="{{ after_link }}">Next page</a></p>
+{% endif %}
 {% if took_ms %}<small>Took {{ took_ms }}</small>{% endif %}
 {% endblock %}

datasette/utils.py

@@ -23,10 +23,10 @@ def path_from_row_pks(row, pks, use_rowid):
     return ','.join(bits)
 
 
-def build_where_clause(args):
+def build_where_clauses(args):
     sql_bits = []
     params = {}
-    for i, (key, values) in enumerate(sorted(args.items())):
+    for i, (key, value) in enumerate(sorted(args.items())):
         if '__' in key:
             column, lookup = key.rsplit('__', 1)
         else:
@@ -45,7 +45,6 @@ def build_where_clause(args):
             'like': '"{}" like :{}',
         }[lookup]
         numeric_operators = {'gt', 'gte', 'lt', 'lte'}
-        value = values[0]
         value_convert = {
             'contains': lambda s: '%{}%'.format(s),
             'endswith': lambda s: '%{}'.format(s),
@@ -59,8 +58,7 @@ def build_where_clause(args):
             template.format(column, param_id)
         )
         params[param_id] = converted
-    where_clause = ' and '.join(sql_bits)
-    return where_clause, params
+    return sql_bits, params
 
 
 class CustomJSONEncoder(json.JSONEncoder):
@@ -103,3 +101,9 @@ def validate_sql_select(sql):
         raise InvalidSql('Statement must begin with SELECT')
     if 'pragma' in sql:
         raise InvalidSql('Statement may not contain PRAGMA')
+
+
+def path_with_added_args(request, args):
+    current = request.raw_args.copy()
+    current.update(args)
+    return request.path + '?' + urllib.parse.urlencode(current)

tests/test_utils.py

@@ -90,7 +90,8 @@ def test_custom_json_encoder(obj, expected):
     ),
 ])
 def test_build_where(args, expected_where, expected_params):
-    actual_where, actual_params = utils.build_where_clause(args)
+    sql_bits, actual_params = utils.build_where_clauses(args)
+    actual_where = ' and '.join(sql_bits)
     assert expected_where == actual_where
     assert {
         'p{}'.format(i): param