Source code for requests_cache.backends.dynamodb

.. image::

`DynamoDB <>`_ is a NoSQL document database hosted on `Amazon Web
Services <>`_. In terms of features and use cases, it is roughly comparable to
MongoDB and other NoSQL databases. It is an especially good fit for serverless applications running
on `AWS Lambda <>`_.

.. warning::
    DynamoDB binary item sizes are limited to 400KB. If you need to cache larger responses, consider
    using a different backend.

Creating Tables
Tables will be automatically created if they don't already exist. This is convienient if you just
want to quickly test out DynamoDB as a cache backend, but in a production environment you will
likely want to create the tables yourself, for example with `CloudFormation
<>`_ or `Terraform <>`_. Here are the
details you'll need:

* Tables: two tables, named ``responses`` and ``redirects``
* Partition key (aka namespace): ``namespace``
* Range key (aka sort key): ``key``
* Attributes: ``namespace`` (string) and ``key`` (string)

Connection Options
The DynamoDB backend accepts any keyword arguments for :py:meth:`boto3.session.Session.resource`:

    >>> backend = DynamoDbCache(region_name='us-west-2')
    >>> session = CachedSession('http_cache', backend=backend)

API Reference
.. automodsumm:: requests_cache.backends.dynamodb
from typing import Dict, Iterable

import boto3
from boto3.dynamodb.types import Binary
from boto3.resources.base import ServiceResource
from botocore.exceptions import ClientError

from .._utils import get_valid_kwargs
from . import BaseCache, BaseStorage

[docs]class DynamoDbCache(BaseCache): """DynamoDB cache backend Args: table_name: DynamoDB table name namespace: Name of DynamoDB hash map connection: :boto3:`DynamoDB Resource <services/dynamodb.html#DynamoDB.ServiceResource>` object to use instead of creating a new one kwargs: Additional keyword arguments for :py:meth:`~boto3.session.Session.resource` """ def __init__( self, table_name: str = 'http_cache', connection: ServiceResource = None, **kwargs ): super().__init__(**kwargs) self.responses = DynamoDbDict(table_name, 'responses', connection=connection, **kwargs) self.redirects = DynamoDbDict( table_name, 'redirects', connection=self.responses.connection, **kwargs )
[docs]class DynamoDbDict(BaseStorage): """A dictionary-like interface for DynamoDB key-value store **Notes:** * The actual table name on the Dynamodb server will be ``namespace:table_name`` * In order to deal with how DynamoDB stores data, all values are serialized. Args: table_name: DynamoDB table name namespace: Name of DynamoDB hash map connection: :boto3:`DynamoDB Resource <services/dynamodb.html#DynamoDB.ServiceResource>` object to use instead of creating a new one kwargs: Additional keyword arguments for :py:meth:`~boto3.session.Session.resource` """ def __init__( self, table_name, namespace='http_cache', connection=None, read_capacity_units=1, write_capacity_units=1, **kwargs, ): super().__init__(**kwargs) connection_kwargs = get_valid_kwargs( boto3.Session.__init__, kwargs, extras=['endpoint_url'] ) self.connection = connection or boto3.resource('dynamodb', **connection_kwargs) self.namespace = namespace try: self.connection.create_table( AttributeDefinitions=[ { 'AttributeName': 'namespace', 'AttributeType': 'S', }, { 'AttributeName': 'key', 'AttributeType': 'S', }, ], TableName=table_name, KeySchema=[ {'AttributeName': 'namespace', 'KeyType': 'HASH'}, {'AttributeName': 'key', 'KeyType': 'RANGE'}, ], ProvisionedThroughput={ 'ReadCapacityUnits': read_capacity_units, 'WriteCapacityUnits': write_capacity_units, }, ) except ClientError: pass self._table = self.connection.Table(table_name) self._table.wait_until_exists()
[docs] def composite_key(self, key: str) -> Dict[str, str]: return {'namespace': self.namespace, 'key': str(key)}
def _scan(self): expression_attribute_values = {':Namespace': self.namespace} expression_attribute_names = {'#N': 'namespace'} key_condition_expression = '#N = :Namespace' return self._table.query( ExpressionAttributeValues=expression_attribute_values, ExpressionAttributeNames=expression_attribute_names, KeyConditionExpression=key_condition_expression, ) def __getitem__(self, key): result = self._table.get_item(Key=self.composite_key(key)) if 'Item' not in result: raise KeyError # Depending on the serializer, the value may be either a string or Binary object raw_value = result['Item']['value'] return self.serializer.loads( raw_value.value if isinstance(raw_value, Binary) else raw_value ) def __setitem__(self, key, value): item = {**self.composite_key(key), 'value': self.serializer.dumps(value)} self._table.put_item(Item=item) def __delitem__(self, key): response = self._table.delete_item(Key=self.composite_key(key), ReturnValues='ALL_OLD') if 'Attributes' not in response: raise KeyError def __iter__(self): response = self._scan() for item in response['Items']: yield item['key'] def __len__(self): return self._table.query( Select='COUNT', ExpressionAttributeNames={'#N': 'namespace'}, ExpressionAttributeValues={':Namespace': self.namespace}, KeyConditionExpression='#N = :Namespace', )['Count']
[docs] def bulk_delete(self, keys: Iterable[str]): """Delete multiple keys from the cache. Does not raise errors for missing keys.""" with self._table.batch_writer() as batch: for key in keys: batch.delete_item(Key=self.composite_key(key))
[docs] def clear(self): self.bulk_delete((k for k in self))