An application can use aContext 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()
  • get_memcache_policy()
  • get_memcache_timeout_policy()
  • set_cache_policy()
  • set_datastore_policy()
  • set_memcache_policy()
  • set_memcache_timeout_policy()
• Memcache and Urlfetch Instance Methods
  • memcache_add()
  • memcache_cas()
  • memcache_decr()
  • memcache_delete()
  • memcache_get()
  • memcache_gets()
  • memcache_incr()
  • memcache_replace()
  • memcache_set()
  • urlfetch()
• Transaction Management Methods
  • call_on_commit()
  • in_transaction()
• 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 aFuture. To wait for the flushing to finish, call this object'swait() method.

get_cache_policy()

Returns the cache policy function. This policy function takes aKey instance argument and returns abool indicating whether the entity with this key should be cached in the in-context cache. May beNone (meaning use default_cache_policy).

get_datastore_policy()

Returns the current context Datastore policy function. This policy function takes aKey instance argument and returns abool indicating if it should use the Datastore. May beNone (meaning use default_datastore_policy).

get_memcache_policy()

Returns the current memcache policy function. This policy function takes aKey instance argument and returns abool indicating if it should be cached. May beNone (meaning use default_memcache_policy).

get_memcache_timeout_policy()

Returns the current memcache timeout policy function. This policy function takes aKey instance argument and returns the desired memcache timeout in seconds (or returns zero to use the default timeout). May beNone, which uses default_memcache_timeout_policy.

set_cache_policy(func)

Sets the cache policy function.

Arguments

func

This function takes aKey instance argument and returns abool indicating whether the entity with this key should be cached in the in-context cache. May beNone.

set_datastore_policy(func)

Sets the Datastore policy function.

Arguments

func

This function takes aKey instance argument and returns abool indicating whether the entity with this key should be stored in the persistent Datastore. May beNone.

set_memcache_policy(func)

Sets the memcache policy function.

Arguments

func

This function takes aKey instance argument and returns abool indicating whether the entity with this key should be cached in the in-context cache. May beNone.

set_memcache_timeout_policy(func)

Sets the memcache timeout policy function.

Arguments

func

This function takes aKey instance argument and returns the desired memcache timeout in seconds (or returns zero to use the default timeout). May beNone.

Memcache and Urlfetch Instance Methods

The full list of methods is found in the Memcache API reference. The list below highlights some of the more commonly used methods:

memcache_add(key,value,time,namespace)

Async auto-batching memcache add().

memcache_cas(key,value,time,namespace)

Async auto-batching memcacheClient cas() (compare-and-swap).

memcache_decr(key,delta,initial_value,namespace)

Async auto-batching memcachedecr().

memcache_delete(key,seconds,namespace)

Async auto-batching memcachedelete().

memcache_get(key,namespace,use_cache)

Async auto-batching memcacheget().

Returns aFuture whose return value is the value retrieved from memcache orNone.

memcache_gets(key,namespace,use_cache)

Async auto-batching memcachegets().

memcache_incr(key,delta,initial_value,namespace)

Async auto-batching memcacheincr().

memcache_replace(key,value,time,namespace)

Async auto-batching memcachereplace().

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

Async auto-batching memcacheset().

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

Async auto-batching urlfetch fetch().

Transaction Management Methods

call_on_commit(callback)

Queues a callback to call upon successful commit of a transaction.

If not in a transaction, the callback is called immediately.

In a transaction, multiple callbacks may be registered and will be called once the transaction commits in the order in which they were registered. If the transaction fails, the callbacks will not be called.

If a callback raises an exception, it bubbles up normally. This means: If the callback is called immediately, any exception it raises will bubble up immediately. If the call is postponed until commit, remaining callbacks will be skipped and the exception will bubble up through thetransaction() call. (However, the transaction is already committed at that point.)

Arguments

callback

Callback function. This callback function takes no parameters and returns nothing.

in_transaction()

ReturnsTrue if this Context represents a transaction,False otherwise.

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, returnNone.

default_datastore_policy(key)

Checks for a_use_datastore class variable on the entity's model class; if there is one, return it. Otherwise, returnNone.

default_memcache_policy(key)

Checks for a_use_memcache class variable on the entity's model class; if there is one, return it. Otherwise, returnNone.

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, returnNone.