Explain IEnumerable vs IQuerable in C#.

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Khushi Singh · Answer

In C#, there are two interfaces, IEnumerable and
IQueryable that are used to for data querying but they vary in where and in what mode, the query is executed. Here's a straightforward comparison:
1. IEnumerable
Namespace: System.Collections
Purpose: For in-memory collection iteration (e.g., List,
Array).
Execution: Queries are executed in-memory after retrieving data from the data source (e.g., database).
Usage: Suitable for querying in-memory data structures like collections.
Performance: Fetches all data into memory before applying filters.
Extension Methods: Works with LINQ-to-Objects.
Example:
IEnumerableandlt;intandgt; numbers = new Listandlt;intandgt; { 1, 2, 3, 4, 5 };
var result = numbers.Where(x =andgt; x andgt; 2); // Filter applied in-memory
2. IQueryable
Namespace: System.Linq
Purpose: For querying data sources like databases using LINQ.
Execution: Queries are translated into SQL (or equivalent) and executed
on the data source (deferred execution).
Usage: Suitable for querying large datasets, especially databases (e.g., Entity Framework).
Performance: Efficient because only the required data is fetched from the source.
Extension Methods: Works with LINQ-to-SQL, LINQ-to-Entities, etc.
Example:
IQueryableandlt;intandgt; query = dbContext.Numbers; // Queryable data source
var result = query.Where(x =andgt; x andgt; 2); // Filter applied on the database
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Explain IEnumerable vs IQuerable in C#.

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