DBCACHE

This small library provides small and simple stores based on postgresql for the following purposes:

• a cache store for bytes with an expiration timestamp
• a key-value store with json serializable values
• a versioned key-value store with values as bytes

To initialize the database schema, type:

$ dbcache init-db postgresql://foo:bar@postgresql/mydb

Example usage (cache):

  from time import sleep
  from datetime import timedelta
  from dbcache.api import dbcache

  cache = dbcache('postgresql://foo:bar@postgresql/mydb')

  assert cache.get('a') is None
  cache.set('a', b'aaa')
  assert cache.get('a') == b'aaa'

  cache.delete('a')
  assert cache.get('a') is None

  cache.set('b', b'bbb', lifetime=timedelta(seconds=1))
  assert cache.get('b') == b'bbb'
  sleep(1)
  assert cache.get('b') is None

Example usage (key/value store):

  from dbcache.api import kvstore
  store = kvstore('postgresql://foo:bar@postgresql/mydb')

  assert store.get('a') is None
  store.set('a', 'aaa')
  assert store.get('a') == 'aaa'
  store.set('a', 'newvalue')
  assert store.get('a') == 'newvalue'

  store.delete('a')
  assert store.get('a') is None

  store.set('int', 42)
  assert store.get('int') == 42

  store.set('float', 42.0)
  store.set('dict', {'a': [1, 2]})

  assert store.all() == {
      'dict': {'a': [1, 2]},
      'float': 42.0,
      'int': 42
  }

  assert store.keys() == ['dict', 'float', 'int']

Example usage (versioned key/value store):

  from dbcache.api import vkvstore
  vstore = vkvstore('postgresql://foo:bar@postgresql/mydb')

  assert vstore.get('html') is None
  v1 = datetime(2023, 1, 1, 12, 30, tzinfo=timezone.utc)
  vstore.set(
      'html',
      b'<html></html>',
      insertion_date=v1
  )
  assert vstore.get('html') == b'<html></html>'

  v2 = datetime(2023, 1, 2, 12, 30, tzinfo=timezone.utc)
  vstore.set(
      'html',
      b'<html>Hello, World</html>',
      insertion_date=v2
  )
  assert vstore.get('html') == b'<html>Hello, World</html>'
  assert vstore.get('html', insertion_date=v1) == b'<html></html>'

  assert vstore.versions('html') == [
      v1,
      v2
  ]
  assert vstore.versions('nope') == []

  vstore.delete('html')
  assert vstore.keys() == []
  assert vstore.get('html') is None