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Dictionary interface to an SQLite database

Project description

sqlitemap

Dictionary interface to an SQLite database.

Build Status Coverage Status PyPI - Downloads PyPI – Version PyPI – Python License

Intro

…One day I needed an embedded key-value store for a pet project, but didn't find a «good enough» implementation. So, I made my own one.

It's a lightweight wrapper over the standard sqlite3 module. It provides the standard MutableMapping interface for an SQLite connection and SQLite table.

Connection

You create an instance of Connection as if it was a normal sqlite3.connect call:

from sqlitemap import Connection

connection = Connection(':memory:', ...)

It implements the context manager interface, so you use with to make a transaction as if it was an sqlite3.Connection. And it implements MutableMapping[str, Collection], except for __setitem__. So you can imagine a Connection as a dictionary of collections altogether with their names and do virtually everything you could do with a normal dict:

from sqlitemap import Collection

# Collection is automatically created:
foo: Collection = connection['foo']

# You can iterate over collection names:
names = list(connection)

# Or even over collections:
collections = connection.values()

# Drop collection:
del connection['foo']

# Get number of collections:
len(connection)

# Special one, to close the connection:
connection.close()

Internally, collection is a table with two columns: key: str and value: bytes. So, you need some serialization to represent objects as byte strings. By default, sqlitemap uses the standard json module. It picks up ujson or orjson, if available. These are also available as sqlitemap extras: sqlitemap[ujson] and sqlitemap[orjson].

Otherwise, you can specify any custom Callable[[Any], bytes] for encoder and Callable[[bytes], Any] for decoder:

connection = Connection(':memory:', dumps_=custom_dumps, loads_=custom_loads)

Collection

Collection also implements the context manager interface to make a transaction, and MutableMapping[str, Any]:

Setting an item

with raises(KeyError):
    _ = collection['foo']
collection['foo'] = 'bar'
assert collection['foo'] == 'bar'
collection['foo'] = 'qux'
assert collection['foo'] == 'qux'

key column is a primary key.

Retrieving keys

assert list(collection) == []
collection['foo'] = 'bar'
assert list(collection) == ['foo']

Retrieving values

assert collection.values() == []
collection['foo'] = 'bar'
assert collection.values() == ['bar']

Deleting an item

with raises(KeyError):
    del collection['foo']
collection['foo'] = 42
del collection['foo']
with raises(KeyError):
    del collection['foo']

Using slices

Collection.__getitem__ and Collection.__setitem__ also support slices as their arguments. Slice start is then converted to key >= start clause, stop to key < stop and step to key LIKE step. All of these are combined with the AND operator. Collection.__getitem__ also applies ORDER BY key clause, so it's possible to make some more sophisticated queries:

collection['bar'] = 1
collection['foo'] = 2
collection['quw'] = 3
collection['qux'] = 4
collection['quy'] = 5
collection['quz'] = 6
assert collection['foo':] == [2, 3, 4, 5, 6]
assert collection[:'foo'] == [1]
assert collection[::'qu%'] == [3, 4, 5, 6]
assert collection['bar':'quz':'qu%'] == [3, 4, 5]

The same also works with del collection [...]. It deletes the rows that would be selected with the corresponding __getitem__ call:

collection['bar'] = 1
collection['foo'] = 2
collection['quw'] = 3
collection['qux'] = 4
collection['quy'] = 5
collection['quz'] = 6
del collection['bar':'quz':'qu%']
assert list(collection) == ['bar', 'foo', 'quz']

Controlling transactions

sqlitemap does nothing special to control transactions. For that refer to the standard library documentation.

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