Entity Framework Core Plus Query Deferred

Description

There are two types of IQueryable extension methods:

Deferred Methods: The query expression is modified but the query is not resolved (Select, Where, etc.). Immediate Methods: The query expression is modified and the query is resolved (Count, First, etc.). However, some third-party features like Query Cache and Query Future cannot be used directly with Immediate Methods since the query is already resolved.

EF+ Query Deferred provides more flexibility to other features.

// Oops! The query is already executed, we cannot cache it.
var count = ctx.Customers.Count();

// Oops! All customers are cached instead of the customer count.
var count = ctx.Customers.FromCache().Count();

Try it

Here comes into play the deferred query which acts exactly like deferred methods, by modifying the query expression without resolving it.

// using Z.EntityFramework.Plus; // Don't forget to include this.
var ctx = new EntitiesContext();

// The count is deferred and cached.
var count = ctx.Customers.DeferredCount().FromCache();

Try it

All LINQ IQueryable extension methods and overloads are supported:

• DeferredAggregate
• DeferredAll
• DeferredAny
• DeferredAverage
• DeferredContains
• DeferredCount
• DeferredElementAt
• DeferredElementAtOrDefault
• DeferredFirst
• DeferredFirstOrDefault
• DeferredLast
• DeferredLastOrDefault
• DeferredLongCount
• DeferredMax
• DeferredMin
• DeferredSequenceEqual
• DeferredSingle
• DeferredSingleOrDefault
• DeferredSum

Options

• Using Query Cache and Query Future
• Execute

Using Query Cache and Query Future

Defer the execution of a query which is normally executed to allow some features like Query Cache and Query Future.

// using Z.EntityFramework.Plus; // Don't forget to include this.
var ctx = new EntitiesContext();

// Query Cache
ctx.Customers.DeferredCount().FromCache();

// Query Future
ctx.Customers.DeferredCount().FutureValue();

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Execute

Execute the deferred query and return the result.

// using Z.EntityFramework.Plus; // Don't forget to include this.
var ctx = new EntitiesContext();

var countDeferred = ctx.Customers.DeferredCount();
var count = countDeferred.Execute();

Try it

Try it (Async version)

Real Life Scenarios

EF Query Deferred brings advantages to other third-party features:

• Allows using Immediate Methods with EF+ Query Cache.
• Allows using Immediate Methods with EF+ Query Future.
• Allows using Immediate Methods with YOUR own features.

Behind the code

When a deferred method is used, the query expression is created exactly like a non-deferred method but instead of invoking the execute method from the query provider, a new instance of a class QueryDeferred is created using the query and the expression.

The QueryDeferred instance has methods to either execute the expression from the query provider or let a third-party library use the object query.

Conclusion

As we saw, EF+ Query Deferred brings considerable advantages to other libraries by letting them use immediate methods without removing any of their features.

Need help getting started? info@zzzprojects.com

We welcome all comments, ideas and suggestions to improve our library.