NDB Context class

An application can use a Context to control its caching policy. Context also offers convenient asynchronous APIs for Memcache and URL Fetch integrated into NDB's asynchronous facilities; in particular, the Memcache API supports auto-batching.

• Cache Management Instance Methods
  • clear_cache()
  • flush()
  • get_cache_policy()
  • get_datastore_policy()
  • set_memcache_policy()
  • set_memcache_timeout_policy()
• Memcache and Urlfetch Instance Methods
  • get_memcache_policy()
  • get_memcache_timeout_policy()
  • memcache_add()
  • memcache_cas()
  • memcache_decr()
  • memcache_delete()
  • memcache_get()
  • memcache_gets()
  • memcache_incr()
  • memcache_replace()
  • memcache_set()
  • set_cache_policy()
  • set_datastore_policy()
  • urlfetch()
• Static Methods
  • default_cache_policy()
  • default_datastore_policy()
  • default_memcache_policy()
  • default_memcache_timeout_policy()

Cache Management Instance Methods

clear_cache()

Clears the in-context cache.

flush()

Flush all auto-batcher queues (sending their work to the servers). The flush happens asynchronously.

Returns a Future. To wait for the flushing to finish, call this object's wait() method.

get_cache_policy()

Returns the cache policy function. This policy function takes a Key instance argument and returns a bool indicating whether the entity with this key should be cached in the in-context cache. May be None (meaning use default_cache_policy).

get_datastore_policy()

Returns the current context Datastore policy function. This policy function takes a Key instance argument and returns a bool indicating if it should use the Datastore. May be None (meaning use default_datastore_policy).

set_memcache_policy(func)

Sets the memcache policy function.

Arguments

func

This function takes a Key instance argument and returns a bool indicating whether the entity with this key should be cached in the in-context cache. May be None.

set_memcache_timeout_policy(func)

Sets the memcache timeout policy function.

Arguments

func

This function takes a Key instance argument and returns the desired memcache timeout in seconds (or returns zero to use the default timeout). May be None.

Memcache and Urlfetch Instance Methods

get_memcache_policy()

Returns the current memcache policy function. This policy function takes a Key instance argument and returns a bool indicating if it should be cached. May be None (meaning use default_memcache_policy).

get_getmemcache_timeout_policy()

Returns the current memcache timeout policy function. This policy function takes a Key instance argument and returns the desired memcache timeout in seconds (or returns zero to use the default timeout). May be None, which uses default_memcache_timeout_policy.

memcache_add(key, value, time, namespace)

Async auto-batching memcache add().

memcache_cas(key, value, time, namespace)

Async auto-batching memcache Client cas() (compare-and-swap).

memcache_decr(key, delta, initial_value, namespace)

Async auto-batching memcache decr().

memcache_delete(key, seconds, namespace)

Async auto-batching memcache delete().

memcache_get(key, namespace, use_cache)

Async auto-batching memcache get().

Returns a Future whose return value is the value retrieved from memcache or None.

memcache_gets(key, namespace, use_cache)

Async auto-batching memcache gets().

memcache_incr(key, delta, initial_value, namespace)

Async auto-batching memcache incr().

memcache_replace(key, value, time, namespace)

Async auto-batching memcache replace().

memcache_set(key, value, time, namespace, use_cache)

Async auto-batching memcache set().

set_cache_policy(func)

Sets the cache policy function.

Arguments

func

This function takes a Key instance argument and returns a bool indicating whether the entity with this key should be cached in the in-context cache. May be None.

set_datastore_policy(func)

Sets the Datastore policy function.

Arguments

func

This function takes a Key instance argument and returns a bool indicating whether the entity with this key should be stored in the persistent Datastore. May be None.

urlfetch(url, payload, method, headers, allow_truncated, follow_redirects, validate_certificate, deadline, callback)

Async auto-batching urlfetch fetch().

Static Methods

default_cache_policy(key)

Checks for a _use_cache class variable on the entity's model class; if there is one, return it. Otherwise, return None.

default_datastore_policy(key)

Checks for a _use_datastore class variable on the entity's model class; if there is one, return it. Otherwise, return None.

default_memcache_policy(key)

Checks for a _use_memcache class variable on the entity's model class; if there is one, return it. Otherwise, return None.

default_memcache_timeout_policy(key)

Checks for a _memcache_timeout class variable on the entity's model class; if there is one, return it. Otherwise, return None.