Entity Framework Plus Query Cache
Caching entities or query results to improve an application's performance is a very frequent scenario. Major ORM like NHibernate had this feature for a long time but, unfortunately for Entity Framework users, second level caching is only available through third party libraries.
Caching is very simple to understand, the first time a query is invoked, data are retrieved from the database and stored in the memory before being returned. All future calls will retrieve data from the memory to avoid making additional database round trips which drastically increases an application's performance.
EF+ Query Cache opens up all caching features for Entity Framework users.
To use caching, simply append to the query "FromCache" method before using an immediate resolution method like "ToList()" or "FirstOrDefault()".
// using Z.EntityFramework.Plus; // Don't forget to include this. var ctx = new EntitiesContext(); // The first call perform a database round trip var countries1 = ctx.Countries.FromCache().ToList(); // Subsequent calls will take the value from the memory instead var countries2 = ctx.Countries.FromCache().ToList();
Real Life Scenarios
- Caching read-only data like application configuration.
- Caching data that can only be modified via an importation like states & countries and make all cache entries related expired once the importation is completed (Tag Expiration).
- Caching data that are frequently accessed but rarely modified like comments and expire the tag when a new comment is added or after one hour without any access (Tag Expiration & Sliding Expiration).
- Caching statistics that don't require to be live like client count and expire them every hour (Absolute Expiration).
Behind the code
When FromCache is invoked, The QueryCacheManager returns the result if a cache entry exists for the cache key. If no cache entry exists, the query is materialized then cached in the memory using the cache key before being returned. If a cache tag is specified, the cache key is also stored in a concurrent dictionary for all tags.
The Cache: The memory cache is used by default.
The Cache Key: The cache key is created by combining a cache prefix, all cache tags and the query expression.
The Query Materialized: The query is materialized by either using "ToList()" method or "Execute()" method for query deferred.
As we have seen, EF+ Query Cache follows a good architecture principle:
- Flexible: Tag & Cache Options make it possible to use Query Cache in a various number of scenarios.
- Extensible: If there is something missing, the library creates your own extension method or your own cache to overcome the problem.
- Maintainable: The easy to use API, documentation and available source code allows new developers to quickly understand this feature.
- Scalable: Caching gets only better as the number of user/traffic grows by drastically reducing database round trip.
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