## Role |
|
This class provides access to cache API of cppcms. It is usually accessed by `cache` member of `application` or `worker_thread`. |
|
In order to use cache, you should [enable it](/wikipp/en/page/ref_config#cache) in CppCMS configurations, otherwise, dummy cache would be used. |
|
## Objects that are stored in cache: |
|
1. Output pages -- including two versions compressed and not for user agents that support gzip compression or not. |
2. HTML Frames -- or simple strings stored in cache. |
3. [Serializable]((/wikipp/en/page/ref_cppcms_serializable) objects. |
|
Each one of them has little bit different semantics and API. |
|
## General |
|
CppCMS provides sophisticated cache system that allows keep its consistency using special triggers that allow cleanup dependent groups of entries using single call. |
|
However, in many cases, timeout only based approach is good enough. So, we would divide the API into two sections: |
|
1. Trigger-less cache access |
2. Full trigger based cache access |
|
|
## Trigger-less cache access |
|
### Web Page |
|
- **`bool fetch_page(string const &key)`** -- fetch page from cache. If it is fetched, `true` is returned and output is prepared, otherwise false is returned. |
|
_Note:_ The output is prepared according to request of user agent --- compressed or not compressed format. Thus, output stream may include already compressed data, so you should not try to append any output after you use this function. |
|
- **`void store_page(string const &key,int timeout=-1);`** -- store prepared output in cache using `timeout` in seconds. |
|
_Note_: default timeout = -1 -- infinite. |
|
For example: |
|
if(cache.fetch_page("main")) |
return; |
... |
render(...) |
cache.store_page("main",3600); |
|
The page can be removed from cache calling: |
|
- **`void rise(string const &key)`** -- that removes data associated with this key. |
|
|
### HTML frames and C++ Objects. |
|
You can fetch such objects using: |
|
bool fetch_frame(string const &key, |
string &result, |
bool notriggers=false); |
bool fetch_data(string const &key, |
serializable &data, |
bool notriggers=false); |
|
_Note:_ Because we work without triggers you should specify `notriggers` as true. |
|
For example: |
|
roles user_roles; // some serializable object |
if(cache.fetch_data("user_"+user_id,user_roles,true)) |
.... |
|
|
You can store these objects using: |
|
void store_frame(string const &key, |
string const &frame, |
int timeout, |
bool notriggers=false); |
void store_data(string const &key, |
serializable const &data, |
int timeout, |
bool notriggers=false); |
|
_Notes:_ |
|
- When working without triggers, specify `notriggers` to `true`, |
- You specify timeout in seconds, when -1 is infinity. |
|
For example: |
|
roles user_roles; // some serializable object |
string key="user_"+user_id; |
if(!cache.fetch_data(key,user_roles,true)) { |
load_user_roles_from_db(user_id,user_roles); |
cache.store_data(key,user_roles,-1,true); |
} |
|
As in case of web pages you can clean data from cache using `void rise(string const &key)` member function. |
