'sqlite-utils enable-counts' command, closes #214

docs/cli.rst

@@ -1057,6 +1057,23 @@ Use the ``--sql`` option to output the SQL that would be executed, rather than r
     order by
         [documents_fts].rank
 
+.. _cli_enable_counts:
+
+Enabling cached counts
+======================
+
+``select count(*)`` queries can take a long time against large tables. ``sqlite-utils`` can speed these up by adding triggers to maintain a ``_counts`` table, see :ref:`python_api_enable_counts`.
+
+The ``sqlite-utils enable-counts`` command can be used to configure these triggers, either for every table in the database or for specific tables.
+
+::
+
+    # Configure triggers for every table in the database
+    $ sqlite-utils enable-counts mydb.db
+
+    # Configure triggers just for specific tables
+    $ sqlite-utils enable-counts mydb.db table1 table2
+
 .. _cli_vacuum:
 
 Vacuum

sqlite_utils/cli.py

@@ -548,6 +548,29 @@ def disable_wal(path, load_extension):
         db.disable_wal()
 
 
+@cli.command(name="enable-counts")
+@click.argument(
+    "path",
+    type=click.Path(exists=True, file_okay=True, dir_okay=False, allow_dash=False),
+    required=True,
+)
+@click.argument("tables", nargs=-1)
+@load_extension_option
+def enable_counts(path, tables, load_extension):
+    "Configure triggers to update a _counts table with row counts"
+    db = sqlite_utils.Database(path)
+    _load_extensions(db, load_extension)
+    if not tables:
+        db.enable_counts()
+    else:
+        # Check all tables exist
+        bad_tables = [table for table in tables if not db[table].exists()]
+        if bad_tables:
+            raise click.ClickException("Invalid tables: {}".format(bad_tables))
+        for table in tables:
+            db[table].enable_counts()
+
+
 def insert_upsert_options(fn):
     for decorator in reversed(
         (

tests/test_enable_counts.py

@@ -1,3 +1,9 @@
+from sqlite_utils import Database
+from sqlite_utils import cli
+from click.testing import CliRunner
+import pytest
+
+
 def test_enable_counts_specific_table(fresh_db):
     foo = fresh_db["foo"]
     assert fresh_db.table_names() == []
@@ -52,3 +58,41 @@ def test_enable_counts_all_tables(fresh_db):
         {"count": 1, "table": "foo_fts_docsize"},
         {"count": 1, "table": "foo_fts_config"},
     ]
+
+
+@pytest.fixture
+def counts_db_path(tmpdir):
+    path = str(tmpdir / "test.db")
+    db = Database(path)
+    db["foo"].insert({"name": "Cleo"})
+    db["bar"].insert({"name": "Cleo"})
+    return path
+
+
+@pytest.mark.parametrize(
+    "extra_args,expected_triggers",
+    [
+        (
+            [],
+            [
+                "foo_counts_insert",
+                "foo_counts_delete",
+                "bar_counts_insert",
+                "bar_counts_delete",
+            ],
+        ),
+        (
+            ["bar"],
+            [
+                "bar_counts_insert",
+                "bar_counts_delete",
+            ],
+        ),
+    ],
+)
+def test_cli_enable_counts(counts_db_path, extra_args, expected_triggers):
+    db = Database(counts_db_path)
+    assert list(db.triggers_dict.keys()) == []
+    result = CliRunner().invoke(cli.cli, ["enable-counts", counts_db_path] + extra_args)
+    assert result.exit_code == 0
+    assert list(db.triggers_dict.keys()) == expected_triggers