## Role |
|
This class provides access to cache API of cppcms; |
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. |
|
|
