EF Core Extension Methods : Query Deferred API

Note

This feature is available in NCache Enterprise and Professional.

In Entity Framework, immediate resolution methods like Count and FirstOrDefault cannot be cached since their expected behavior is to cache the count result or only the first item. The NCache EF Core Extension Methods offer deferred queries to resolve this issue. The resolution is deferred instead of being immediate which caches the expected result instead of the entities themselves. This means that the deferred APIs have dedicated FromCache and FromCacheOnly APIs that cache the result.

Points to be noted about this API:

• Query deferred results cannot be stored as separate entities as they are not entities themselves so the Cache.Insert API will fail for them.

• FromCache and LoadIntoCache ignore StoreAs in CachingOptions for query deferred APIs.

• FromCacheOnly only supports Aggregate operators in QueryDeferred.

Aggregate Operators

Aggregate operators are supported by both methods: FromCache and FromCacheOnly.

Operator	Example
DeferredAverage	database.Products.Select(o => o.UnitPrice).DeferredAverage().FromCache(options);
DeferredCount	database.Customers.Select(c => c.Country).GroupBy(c => c).DeferredCount().FromCacheOnly();
DeferredMin	database.Orders.Where(o => o.CustomerId == "VINET").Select(o => o.RequiredDate).DeferredMin().FromCache(options);
DeferredMax	database.Orders.Select(o => o.RequiredDate).DeferredMax().FromCacheOnly();
DeferredSum	database.OrderDetails.Select(o => o.UnitPrice).DeferredSum().FromCache(options);

Element Operators

Element operators are only supported by FromCache().

Operator	Example
DeferredElementAtOrDefault	database.Customers.DeferredElementAtOrDefault(c => c.City == "London").FromCache(options);
DeferredFirst	database.Customers.DeferredFirst(c => c.ContactTitle == "Sales Representative").FromCache(options);
DeferredFirstOrDefault	database.Customers.DeferredFirstOrDefault(c => c.ContactTitle == "Sales Representative").FromCache(options);
DeferredLast	database.Customers.DeferredLast(c => c.City == "London").FromCache(options);
DeferredLastOrDefault	database.Customers.DeferredLastOrDefault(c => c.City == "London").FromCache(options);
DeferredSingle	database.Customers.DeferredSingle(c => c.CustomerId == "ALFKI").FromCache(options);
DeferredSingleOrDefault	database.Customers.DeferredSingleOrDefault(c => c.CustomerId == "ANATR").FromCache(options);

Miscellaneous LINQ Operators

The following operators are only supported by FromCache().

Operator	Example
DeferredAll	database.Products.DeferredAll(expression).FromCache(options);
DeferredLongCount	database.Products.DeferredLongCount().FromCache(options);
DeferredContains	database.Products.DeferredContains(new Products { ProductId = 1 });

See Also

Caching Options for EF Core Caching
EF Core Caching Extension Methods
Cache Handle from EF Core Context
Logging Entity Framework Core Caching