Posts Tagged ‘Language Integrated Query’

What is the difference between IEnumerable and IQueryable

March 12, 2013 1 comment

In LINQ to query data from database and collections, we use IEnumerable and IQueryable for data manipulation. IEnumerable is inherited by Iqueryable, hence it has all the features of it and except this, it has its own features. Both have its own importance to query data and data manipulation. Let’s see both the features and take the advantage of both the features to boost your LINQ Query performance.

IEnumerable  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


How does it work While querying data from database, IEnumerable execute 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 execute 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 supports. Supports using CreateQuery and Execute methods.
Extension mehtod
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

IEnumerable Example

MyDataContext dc = new MyDataContext ();
IEnumerable<Employee> list = dc.Employees.Where(p => p.Name.StartsWith(“S”));
list = list.Take<Employee>(10);

Generated SQL statements of above query will be:

SELECT [t0].[EmpID], [t0].[EmpName], [t0].[Salary] FROM [Employee] AS [t0]
WHERE [t0].[EmpName] LIKE @p0

IQueryable Example

MyDataContext dc = new MyDataContext ();
IQueryable<Employee> list = dc.Employees.Where(p => p.Name.StartsWith(“S”));
list = list.Take<Employee>(10);

Generated SQL statements of above query will be:

SELECT TOP 10 [t0].[EmpID], [t0].[EmpName], [t0].[Salary] FROM [Employee] AS [t0]
WHERE [t0].[EmpName] LIKE @p0

Hope it helps!

Tips to improve Entity Framework Performance

March 12, 2013 14 comments

LINQ to Entity is a great ORM for querying and managing database. It offers a lot of things, so it is mandatory to know about performance of it. These are right up to a certain point as LINQ comes with its own penalties. There are some tips and tricks that we should keep in mind while designing and query database using entity framework ORM. Here is a list of some tips that I would like to share with you.

  1. Avoid to put all the DB Objects into One Single Entity Model

    Entity Model specifies a single unit of work, not all our database. If we have many database objects that are not connected to one another or these(log tables, objects used by batch processes etc.) are not used at all. Hence these objects are consuming space in the memory and cause performance degrades. So try to make separate entity models of related database objects.

  2. Disable change tracking for entity if not needed

    Whenever you retrieve the data only for reading purpose, not for modification then there is no need of object tracking. So disable object tracking by using MergeOption as below:

    NorthwindDataContext context = new NorthwindDataContext();

    context.tblCities.MergeOption = MergeOption.NoTracking;

    This option allows us to turn off the object cache and unnecessary identity management of the objects.

  3. Use Pre-Generating Views to reduce response time for first request

    When the object of ObjectContext is created first time in the application, the entity framework creates a set of classes that is required to access the database. This set of classes is called view and if your data model is large then creating the view may delay the web application response to the first request for a page. We can reduce this response time by creating view at compile time by using T4 template or EdmGen.exe command-line tool.

  4. Avoid fetching all the fields if not required

    Avoid fetching not required fields from the database. Suppose I have table of Customer with 20 fields and I am interested only in three fields – CustomerID, Name, Address then fetch only these three fields instead of fetching all the fields of the Customer table.

    //Bad Practice

    var customer =

    (from cust in dataContext.Customers

    select cust).ToList();

    //Good Practice

    var customerLite =

    (from cust in dataContext.Customers

    select new {

    customer. CustomerID,



    }). ToList ();

  5. Choose appropriate Collection for data manipulation

    In linq we have Var, IEnumerable, IQueryable, IList type collection for data manipulation. Each collection has its importance and performance impact on the query, so beware of using all these collection for data manipulation.

  6. Use Compiled Query wherever needed

    Make a query to compiled query if it is frequently used to fetch records from the database. This query is slow in first time but after that it boost the performance significantly. We use Compile method of CompiledQuery class for making compiled query.

    Suppose you required to retrieve customers details again and again based on city then make this query to compiled query like as

    // create the entity object

    NorthwindEntities mobjentity = new NorthwindEntities();

    //Simple Query

    IQueryable lstCus = from customer in mobjentity.tblCustomers

    where customer.City == “Delhi”

    select customer;

    //Compiled Query

    Func> compiledQuery

    = CompiledQuery.Compile>(

    (ctx, city) =>from customer in ctx.Customers

    where customer.City == city

    select customer);

    In above query we are passing the string parameter city for filtering the records.

  7. Retrieve only required number of records

    When we are binding data to grid or doing paging, retrieve only required no of records to improve performance. This can achieved by using Take,While and Skip methods.

    // create the entity object

    NorthwindEntities mobjentity = new NorthwindEntities();

    int pageSize=10,startingPageIndex=2;

    List lstCus = mobjentity.tblCustomers.Take(pageSize)

    .Skip(startingPageIndex * pageSize)


  8. Avoid using Contains

    In LINQ, we use contains method for checking existence. It is converted to “WHERE IN” in SQL which cause performance degrades.

  9. Avoid using Views

    Views degrade the LINQ query performance costly. These are slow in performance and impact the performance greatly. So avoid using views in LINQ to Entities.

  10. Debug and Optimize LINQ Query

    If you want to debug and optimize your query then LINQ Pad is a great tool for this purpose. I am a big fan of LINQ Pad. It is very useful for query construction, debugging and optimization.

    IQueryable lstCus = from customer in mobjentity.tblCustomers

    where customer.City == “Delhi”

    select customer;


    Dump method of LINQ Pad give the result of above query in the result window.