apswutils

Tip

Where to find the complete documentation for this library

If you want to learn about everything this project can do, we recommend reading the Python library section of the sqlite-utils project here.

This project wouldn’t exist without Simon Willison and his excellent sqlite-utils project. Most of this project is his code, with some minor changes made to it.

Install

pip install apswutils

Use

First, import the apswutils library. Through the use of the all attribute in our Python modules by using import * we only bring in the Database, Queryable, Table, View classes. There’s no risk of namespace pollution.

from apswutils.db import *

Then we create a SQLite database. For the sake of convienance we’re doing it in-memory with the :memory: special string. If you wanted something more persistent, name it something not surrounded by colons, data.db is a common file name.

db = Database(":memory:")

Let’s drop (aka ‘delete’) any tables that might exist. These docs also serve as a test harness, and we want to make certain we are starting with a clean slate. This also serves as a handy sneak preview of some of the features of this library.

for t in db.tables: t.drop()

User tables are a handy way to create a useful example with some real-world meaning. To do this, we first instantiate the users table object:

users = Table(db, 'Users')
users

<Table Users (does not exist yet)>

The table doesn’t exist yet, so let’s add some columns via the Table.create method:

users.create(columns=dict(id=int, name=str, age=int))
users

<Table Users (id, name, age)>

What if we need to change the table structure?

For example User tables often include things like password field. Let’s add that now by calling create again, but this time with transform=True. We should now see that the users table now has the pwd:str field added.

users.create(columns=dict(id=int, name=str, age=int, pwd=str), transform=True, pk='id')
users

<Table Users (id, name, age, pwd)>

print(db.schema)

CREATE TABLE "Users" (
   [id] INTEGER PRIMARY KEY,
   [name] TEXT,
   [age] INTEGER,
   [pwd] TEXT
);

Queries

Let’s add some users to query:

users.insert(dict(name='Raven', age=8, pwd='s3cret'))
users.insert(dict(name='Magpie', age=5, pwd='supersecret'))
users.insert(dict(name='Crow', age=12, pwd='verysecret'))
users.insert(dict(name='Pigeon', age=3, pwd='keptsecret'))
users.insert(dict(name='Eagle', age=7, pwd='s3cr3t'))

<Table Users (id, name, age, pwd)>

A simple unfiltered select can be executed using rows property on the table object.

users.rows

<generator object Queryable.rows_where>

Let’s iterate over that generator to see the results:

[o for o in users.rows]

[{'id': 1, 'name': 'Raven', 'age': 8, 'pwd': 's3cret'},
 {'id': 2, 'name': 'Magpie', 'age': 5, 'pwd': 'supersecret'},
 {'id': 3, 'name': 'Crow', 'age': 12, 'pwd': 'verysecret'},
 {'id': 4, 'name': 'Pigeon', 'age': 3, 'pwd': 'keptsecret'},
 {'id': 5, 'name': 'Eagle', 'age': 7, 'pwd': 's3cr3t'}]

Filtering can be done via the rows_where function:

[o for o in users.rows_where('age > 3')]

[{'id': 1, 'name': 'Raven', 'age': 8, 'pwd': 's3cret'},
 {'id': 2, 'name': 'Magpie', 'age': 5, 'pwd': 'supersecret'},
 {'id': 3, 'name': 'Crow', 'age': 12, 'pwd': 'verysecret'},
 {'id': 5, 'name': 'Eagle', 'age': 7, 'pwd': 's3cr3t'}]

We can also limit the results:

[o for o in users.rows_where('age > 3', limit=2)]

[{'id': 1, 'name': 'Raven', 'age': 8, 'pwd': 's3cret'},
 {'id': 2, 'name': 'Magpie', 'age': 5, 'pwd': 'supersecret'}]

The offset keyword can be combined with the limit keyword.

[o for o in users.rows_where('age > 3', limit=2, offset=1)]

[{'id': 2, 'name': 'Magpie', 'age': 5, 'pwd': 'supersecret'},
 {'id': 3, 'name': 'Crow', 'age': 12, 'pwd': 'verysecret'}]

The offset must be used with limit or raise a ValueError:

try:
    [o for o in users.rows_where(offset=1)]
except ValueError as e:
    print(e)

Cannot use offset without limit

Transactions

If you have any SQL calls outside an explicit transaction, they are committed instantly.

To group 2 or more queries together into 1 transaction, wrap them in a BEGIN and COMMIT, executing ROLLBACK if an exception is caught:

users.get(1)

{'id': 1, 'name': 'Raven', 'age': 8, 'pwd': 's3cret'}

db.begin()
try:
    users.delete([1])
    db.execute('FNOOORD')
    db.commit()
except Exception as e:
    print(e)
    db.rollback()

near "FNOOORD": syntax error

Because the transaction was rolled back, the user was not deleted:

users.get(1)

{'id': 1, 'name': 'Raven', 'age': 8, 'pwd': 's3cret'}

Let’s do it again, but without the DB error, to check the transaction is successful:

db.begin()
try:
    users.delete([1])
    db.commit()
except Exception as e: db.rollback()

try:
    users.get(1)
    print("Delete failed!")
except: print("Delete succeeded!")

Delete succeeded!

Differences from sqlite-utils and sqlite-minutils

• WAL is the default
• Setting Database(recursive_triggers=False) works as expected
• Primary keys must be set on a table for it to be a target of a foreign key
• Errors have been changed minimally, future PRs will change them incrementally

Differences in error handling

Old/sqlite3/dbapi	New/APSW	Reason
IntegrityError	apsw.ConstraintError	Caused due to SQL transformation blocked on database constraints
sqlite3.dbapi2.OperationalError	apsw.Error	General error, OperationalError is now proxied to apsw.Error
sqlite3.dbapi2.OperationalError	apsw.SQLError	When an error is due to flawed SQL statements
sqlite3.ProgrammingError	apsw.ConnectionClosedError	Caused by an improperly closed database file