Click here to Skip to main content

Technical Blog

IEnumerable Vs IQueryable

Adarsh Chaurasia - Passionate Trainer

Rate me:

4.82/5 (103 votes)

24 Feb 2014CPOL1 min read

262K

49

13

IEnumerable Vs IQueryable

Many developers get confused between IEnumerable and IQueryable. When it comes to writing code, both look very similar. However, there are many differences between them which need to be taken care of while writing code. Both have some intended usability scenarios for which they are made.

Listed below are the differences between them based on their properties:

	IEnumerable	IQueryable
Namespace	`System.Collections` Namespace	`System.Linq` Namespace
Derives from	No base interface	Derives from `IEnumerable`
Deferred Execution	Supported	Supported
Lazy Loading	Not Supported	Supported
How does it work	While querying data from database, `IEnumerable` executes `select` query on server side, load data in-memory on client side and then filter data. Hence does more work and becomes slow.	While querying data from database, `IQueryable` executes `select` query on server side with all filters. Hence does less work and becomes fast.
Suitable for	LINQ to Object and LINQ to XML queries	LINQ to SQL queries
Custom Query	Doesn’t support	Supports using `CreateQuery` and `Execute` methods
Extension method parameter	Extension methods supported in `IEnumerable` takes functional objects.	Extension methods supported in `IEnumerable` takes expression objects, i.e., expression tree.
When to use	When querying data from in-memory collections like `List`, `Array`, etc.	When querying data from out-memory (like remote database, service) collections.
Best Uses	In-memory traversal	Paging

This article was originally posted at http://synvistech.com/blogs/ienumerable-vs-iqueryable

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Comments and Discussions

IEnumerable VS IQueryable

LINQ to query data from database and collections, we use IEnumerable and IQueryable for data manipulation. IEnumerable is inherited by IQueryable, Hence IQueryable has all the features of IEnumerable and except this, it has its own features. Both have its own importance to query data and data manipulation. Let’s see both the fetures and take the advantage of both the fetures to boost your LINQ Query performance.
IEnumerable
1. IEnumerable exists in System.Collections Namespace.
2. IEnumerable can move forward only over a collection, it can’t move backward and between the items.
3. IEnumerable is best to query data from in-memory collections like List, Array etc.
4. While query data from database, IEnumerable execute select query on server side, load data in-memory on client side and then filter data.
5. IEnumerable is suitable for LINQ to Object and LINQ to XML queries.
6. IEnumerable supports deferred execution.
7. IEnumerable doesn’t supports custom query.
8. IEnumerable doesn’t support lazy loading. Hence not suitable for paging like scenarios.
9. Extension methods supports by IEnumerable takes functional objects.
IEnumerable Example
1. MyDataContext dc = new MyDataContext ();
2. IEnumerable<Employee> list = dc.Employees.Where(p => p.Name.StartsWith("S"));
3. list = list.Take<Employee>(10);
Generated SQL statements of above query will be :
1. SELECT [t0].[EmpID], [t0].[EmpName], [t0].[Salary] FROM [Employee] AS [t0]
2. WHERE [t0].[EmpName] LIKE @p0
Notice that in this query "top 10" is missing since IEnumerable filters records on client side
IQueryable
1. IQueryable exists in System.Linq Namespace.
2. IQueryable can move forward only over a collection, it can’t move backward and between the items.
3. IQueryable is best to query data from out-memory (like remote database, service) collections.
4. While query data from database, IQueryable execute select query on server side with all filters.
5. IQueryable is suitable for LINQ to SQL queries.
6. IQueryable supports deferred execution.
7. IQueryable supports custom query using CreateQuery and Execute methods.
8. IQueryable support lazy loading. Hence it is suitable for paging like scenarios.
9. Extension methods supports by IQueryable takes expression objects means expression tree.
IQueryable Example
1. MyDataContext dc = new MyDataContext ();
2. IQueryable<Employee> list = dc.Employees.Where(p => p.Name.StartsWith("S"));
3. list = list.Take<Employee>(10);
Generated SQL statements of above query will be :
1. SELECT TOP 10 [t0].[EmpID], [t0].[EmpName], [t0].[Salary] FROM [Employee] AS [t0]
2. WHERE [t0].[EmpName] LIKE @p0
Notice that in this query "top 10" is exist since IQueryable executes query in SQL server with all filters.

General News Suggestion Question Bug Answer Joke Praise Rant Admin

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

Go to top