Entity framework

1. Entity
Framework
Optimization
By Rajeev Harbola

2. Design Consideration
 Avoid to put all the DB Objects into One Single Entity Model.
 Disable change tracking for entity if not needed.
NorthwindDataContext context = new NorthwindDataContext()
context.tblCities.MergeOption = MergeOption.NoTracking;
 Avoid fetching all the fields if not required
//Bad Practice
var customer = (from cust in dataContext.Customers select cust).ToList();
//Good Practice
var customer = (from cust in dataContext.Customers
select new {
customer. CustomerID,customer.Name,customer.Address}ToList ();
 Use Compiled Query wherever needed

3. Design Consideration
• Avoid using Contains
• Retrieve only required number of records.

4. Coding Guidelines
• Do Not Count After Query Execution
var empCount = db.Employees .Where(x => x.CreateDate <
DateTime.Now.AddDays(-10) .Count() //only executes a SQL COUNT
var emps = db.Employees .Where(x => x.CreateDate <
DateTime.Now.AddDays(-10)
var empCount = emps.Count() // returns all matching employees and
then executes a count
• Filter Before ToList()
//ToList() executed too early
var emps = db.Employees .Where(x => x.CreateDate <
DateTime.Now.AddDays(-10) .ToList() // All employees created within last 10 days queried
.Take(50) // List is filtered for the top 50
//ToList() executed last
var emps = db.Employees .Where(x => x.CreateDate <
DateTime.Now.AddDays(-10) .Take(50) .ToList() //Query made for top
50 employees created within last 10 days

5. Coding Guidelines
• Don’t Load Entities To Delete Them (very important)
var emp = db.Employees.Find(empID); //Executes a query against the database
db.Employees.Remove(emp);
db.SaveChanges(); //Executes a second hit to the database
var emp = new Employee { ID = empID }
db.Employees.Attach(emp);
db.Employees.Remove(emp);
db.SaveChanges(); //Executes a single hit to the database
• Use Eager Loading Instead of Lazy Loading
var employees = db.Employees; foreach(var emp in employees)
{
var address = emp.Address; //Database query is executed every time this line is hit
}
var employees = db.Employees .Include(x => x.Address) .ToList(); //All data loaded from
database
foreach(var emp in employees)
{
var address = emp.Address; //No database query executed
}

6. Coding Guidelines
• Query In-Memory Entities First
var emp = db.Employees.Find(empID); //Executes a query against the database
db.Employees.Remove(emp);
db.SaveChanges(); //Executes a second hit to the database
var emp = new Employee { ID = empID }
db.Employees.Attach(emp);
db.Employees.Remove(emp);
db.SaveChanges(); //Executes a single hit to the database
• Use Eager Loading Instead of Lazy Loading
var emp = db.Employees.Find(empID); // Queries in memory first
var emp = db.Employees.Where(x => x.ID == empID); //Always hits the database
var emp = db.Employees.Local.Where(x => x.ID == empID) ;

7. Advanced
• Use Compiled Query wherever needed
// 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);
• Debug and Optimize LINQ Query
IQueryable lstCus = from customer in mobjentity.tblCustomers
where customer.City == "Delhi"
select customer;
lstCus.Dump();

8. Last but not least
• Don’t Rely on Entity Framework Exclusively For Data
Access
• Finally, EF is great for productivity but executing raw SQL
or a stored procedure may often produce performance
benefits.
• In EF 4.0 and above the DbContext the SQLQuery()
method to execute raw SQL:
• var emps = db.Database.SQLQuery("select email from
Employees");Similarly use ExecuteSqlCommand() to
execute a stored procedure:
• var emps = db.Database.ExecuteSqlCommand("...");

9. THANKS
&
No question please