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IQueryable
C# developers often encounter IQueryable<T>
and IEnumerable<T>
when working with collections. Understanding their differences is crucial for writing efficient LINQ queries.
The Shared Trait: Deferred Execution
Both IQueryable<T>
and IEnumerable<T>
employ deferred execution. This means the query isn't executed until its results are actually needed, enhancing efficiency.
The Key Difference: Database Interaction
The core distinction lies in their execution context. IQueryable<T>
works with LINQ-to-database (like LINQ-to-SQL or Entity Framework), allowing query refinement within the database itself. This significantly improves performance by minimizing data transferred to memory.
Conversely, IEnumerable<T>
uses LINQ-to-objects. This means the entire dataset matching the initial query is loaded into memory before any further processing.
When to Use IQueryable
Opt for IQueryable<T>
when:
When to Use IEnumerable
Choose IEnumerable<T>
when:
ToList()
, ForEach()
, etc., which operate on in-memory collections.Illustrative Example: Paging with IQueryable
Consider a paging scenario:
<code class="language-csharp">var goldCustomers = db.Customers .Where(c => c.City == "<city>") .Skip(pageNumber * pageSize) .Take(pageSize);</code>
With IQueryable<T>
, Skip
and Take
are executed within the database, retrieving only the necessary page. Using IEnumerable<T>
, all customers from the specified city would be loaded into memory first, resulting in significantly lower efficiency. Therefore, IQueryable<T>
is the preferred choice for scenarios involving large datasets and paging.
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