What is the difference between IEnumerable and IQueryable?

Question

ICSM Computer · Answer

IEnumerableandlt;Tandgt;
Namespace: System.Collections.GenericPurpose: Represents a sequence of elements that can be enumerated (iterated) over in memory.Execution: Deferred execution in memory.Use case: Best for in-memory collections like arrays, lists, or already-fetched data.Query execution: LINQ to Objects – the query is executed
in the application, after fetching data.
Example:
Listandlt;intandgt; numbers = new Listandlt;intandgt; { 1, 2, 3, 4 };
IEnumerableandlt;intandgt; evens = numbers.Where(n =andgt; n % 2 == 0); // Executed in memory
Characteristics:
Supports only LINQ to Objects.Filters are applied after retrieving all data into memory.Less suitable for large data sources like databases.
IQueryableandlt;Tandgt;
Namespace: System.LinqPurpose: Enables querying a data source (e.g., database) with
expression trees that can be translated to the native query language (e.g., SQL).Execution: Deferred execution on the data source.Use case: Best for querying remote data sources (e.g., Entity Framework, LINQ to SQL).Query execution: LINQ to Entities, 
SQL, or other providers.
Example:
IQueryableandlt;Userandgt; users = dbContext.Users.Where(u =andgt; u.Age andgt; 30); // Translates to SQL
Characteristics:
Converts LINQ queries into SQL and executes them on the server.Efficient for databases because it can perform filtering, joining, paging, etc., on the server.Ideal for large datasets or when you want to avoid loading unnecessary data.
Key Differences
Feature
IEnumerableandlt;Tandgt;
IQueryableandlt;Tandgt;
Namespace
System.Collections.Generic
System.Linq
Query execution
In memory (client-side)
At data source (server-side)
Use with databases
Not suitable
Yes (e.g., Entity Framework)
Deferred execution
Yes
Yes
Query translation
N/A
Translates expression trees to SQL
Performance
May fetch all records
Efficient due to server-side filtering
Summary
Use IEnumerableandlt;Tandgt; when working with in-memory collections.Use IQueryableandlt;Tandgt; when working with databases or external data sources to avoid pulling too much data into memory.

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What is the difference between IEnumerable and IQueryable?

ICSM Computer

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1 Answers

`IEnumerable<T>`

Example:

Characteristics:

`IQueryable<T>`

Example:

Characteristics:

Key Differences

Summary

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Feature	`IEnumerable<T>`	`IQueryable<T>`
Namespace	`System.Collections.Generic`	`System.Linq`
Query execution	In memory (client-side)	At data source (server-side)
Use with databases	Not suitable	Yes (e.g., Entity Framework)
Deferred execution	Yes	Yes
Query translation	N/A	Translates expression trees to SQL
Performance	May fetch all records	Efficient due to server-side filtering