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What is the purpose of the "AsEnumerable" and "AsQueryable" methods in LINQ?

Sandra Emily7612-Sep-2023

What is the purpose of the 'AsEnumerable' and 'AsQueryable' methods in LINQ?

c#c# linq linq to sql 
Updated on 25-Sep-2023
Sandra Emily

Sandra Emily

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Aryan Kumar

Aryan Kumar

25-Sep-2023

In LINQ (Language Integrated Query), the AsEnumerable() and AsQueryable() methods are used to change the data source type temporarily during a query. They are typically used to cast or adapt an existing collection or data source to a different interface type, depending on the requirements of the query and the underlying data source.

Here's a brief explanation of the purpose and use cases for both methods:

AsEnumerable():

  • Purpose: The AsEnumerable() method is primarily used to convert a data source or collection into an IEnumerable<T>. This is often done to shift the query processing from being database-specific (if you're using LINQ to Entities or LINQ to SQL) to in-memory processing using LINQ to Objects.
  • Use Cases:
    • When you want to perform further LINQ operations on the data in memory after retrieving it from a database. This can be useful when you want to use LINQ to Objects methods that are not supported in LINQ to Entities or LINQ to SQL.
    • To transition from a database query to an in-memory query while maintaining deferred execution (i.e., postponing the execution of the query until it's actually needed).
var query = dbContext.Orders
                  .Where(order => order.CustomerId == customerId)
                  .AsEnumerable()
                  .Where(order => order.OrderDate.Year == 2023)
                  .ToList();

AsQueryable():

  • Purpose: The AsQueryable() method is used to convert an IEnumerable<T> or any other collection type into an IQueryable<T>. This is often done to enable query composition and deferred execution when working with in-memory collections or other non-queryable data sources.
  • Use Cases:
    • When you want to apply additional query operations (such as filtering, sorting, or projecting) on an in-memory collection and want to leverage deferred execution, which allows you to compose complex queries efficiently.
    • To bridge the gap between LINQ to Objects and LINQ to Entities, making it possible to use common query operators on both types of data sources.

Example:

var queryableData = inMemoryCollection.AsQueryable();
var result = queryableData.Where(item => item.SomeProperty == someValue).OrderBy(item => item.OtherProperty);

In summary, AsEnumerable() is used to switch from a queryable data source (e.g., database) to an in-memory collection for further processing, while AsQueryable() is used to introduce queryability to an in-memory collection, allowing you to apply LINQ operations with deferred execution. The choice between these methods depends on whether you want to transition from queryable to in-memory or vice versa and whether you need deferred execution or not.

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