Support STRICT tables

[simonw]

New in SQLite 3.37.0, released a few days ago: https://www.sqlite.org/stricttables.html

[simonw]

From that page:

If you try to open a database containing the STRICT keyword in an earlier version of SQLite, it will not recognize the keyword and will report an error (except as noted below.

[...]

Because of a quirk in the SQL language parser, versions of SQLite prior to 3.37.0 can still read and write STRICT tables if they set "PRAGMA writable_schema=ON" immediately after opening the database file, prior to doing anything else that requires knowing the schema.

[simonw]

I'm going to build my own pysqlite3 wheel with the latest SQLite to try this out, following the instructions on https://github.com/coleifer/pysqlite3

[simonw]

This worked:

cd /tmp
mkdir sqlite-3.37
cd sqlite-3.37
wget 'https://www.sqlite.org/2021/sqlite-amalgamation-3370000.zip'
unzip sqlite-amalgamation-3370000.zip
git clone https://github.com/coleifer/pysqlite3/
cp sqlite-amalgamation-3370000/sqlite3.[ch] pysqlite3
cd pysqlite3
python3 setup.py build_static build bdist_wheel

This gave me a file here:

pysqlite3 % ls -l dist  
total 1872
-rw-r--r--  1 simon  wheel  956557 Nov 29 12:38 pysqlite3-0.4.6-cp39-cp39-macosx_10_15_x86_64.whl

That wheel only works when installed for Python 3.9 (it failed to install in a Python 3.10 virtual environment) - but pip install /tmp/sqlite-3.37/pysqlite3/dist/pysqlite3-0.4.6-cp39-cp39-macosx_10_15_x86_64.whl gave me a working pysqlite3 - and the following worked:

>>> import pysqlite3
>>> pysqlite3.connect(":memory:").execute("select sqlite_version()").fetchall()
[('3.37.0',)]

And if I install sqlite-utils in the same virtual environment this works:

% sqlite-utils memory 'select sqlite_version()'
[{"sqlite_version()": "3.37.0"}]

[simonw]

There are a few places that the strict=True option could go:

• table.create() and table.create_table_sql()
• The Database() constructor, to turn it on for all created tables
• The .insert() / .insert_all() etc family of methods that can implicitly create tables

I'll definitely implement the first one, and likely the second one too. I'm on the fence with regards to the third one.

[simonw]

What should happen if you attempt to use strict=True against a SQLite version prior to 3.37.0?

An obvious error would be best... but how about silently ignoring it on older versions instead? That would match how we handle deterministic=True for registering functions:

sqlite-utils/sqlite_utils/db.py

Lines 372 to 380 in 1267037

	def register(fn):
	name = fn.__name__
	arity = len(inspect.signature(fn).parameters)
	if not replace and (name, arity) in self._registered_functions:
	return fn
	kwargs = {}
	if deterministic and sys.version_info >= (3, 8):
	kwargs["deterministic"] = True
	self.conn.create_function(name, arity, fn, **kwargs)

sqlite-utils/tests/test_register_function.py

Lines 34 to 37 in 93c7fd9

	@pytest.mark.skipif(
	sys.version_info < (3, 8), reason="deterministic=True was added in Python 3.8"
	)
	def test_register_function_deterministic_registered(fresh_db):

[simonw]

I'm leaning towards silently ignore if SQLite version doesn't support it. That means that the first time you attempt to use strict=True we will need to run a test against the database connection to see what version of SQLite it uses, then cache the result to avoid making the same call again for the same connection.

[simonw]

Is there a need for an introspection function for telling if a SQLite table is in strict mode or not? How would that work?

[simonw]

From the STRICT docs:

The SQLite parser accepts a comma-separated list of table options after the final close parenthesis in a CREATE TABLE statement. As of this writing (2021-08-23) only two options are recognized:

• STRICT
• WITHOUT ROWID

So I think I need to read the CREATE TABLE statement from the sqlite_master table, split on the last ), split those tokens on , and see if create is in there (case insensitive).

[simonw]

Made myself a test strict table like so:

>>> import pysqlite3
>>> conn = pysqlite3.connect("/tmp/strict-table.db")
>>> conn.execute("create table foo (id integer primary key, name text, weight real) strict")
<pysqlite3.dbapi2.Cursor object at 0x104317340>
>>> cursor = conn.cursor()
>>> with conn:
...     cursor.execute("insert into foo (name, weight) values ('Lila', '2.31')")
<pysqlite3.dbapi2.Cursor object at 0x10331e1f0>
>>> conn.close()

Uploaded that to: https://static.simonwillison.net/static/2021/strict-table.db

[simonw]

Here's a function that detects if strict is supported or not:

import secrets
import sqlite3

def supports_strict_tables(db = None):
    if db is None:
        db = sqlite3.connect(":memory:")
    try:
        table_name = 't{}'.format(secrets.token_hex(16))
        with db:
            db.execute("create table {} (name text) strict".format(table_name))
            db.execute("drop table {}".format(table_name))
        return True
    except:
        return False

[simonw]

I'm going to add that as db.supports_strict.

[simonw]

I haven't documented db.supports_strict yet (I documented table.strict) because there wasn't an obvious section of the documentation for it.

I need to remember to document it once I add documentation for the strict=True parameter.

[simonw]

Need to figure out a good pattern for testing this in CI too - it will currently skip the new tests if it doesn't have SQLite 3.37 or higher.

[tkhattra]

hello Simon,

I've added more STRICT table support per #344 (comment) in changeset e4b9b58.
It also fixes table.transform() to preserve STRICT mode.
Please pull if you deem appropriate. Thanks!