Entity Framework Questions & Answers

1)    Explain what is Entity framework?

·         Entity framework is an ORM framework that is Object Relational Mapper

·         It is an open source framework. ORM helps us to maintain database mapping and can do DB operation in Code side.

·         Entity framework is developed by Microsoft

·         It just map our Database tables to model entities and perform the operation

·         Entity framework is an ORM which creates an higher abstract object model over Ado.Net components so rather that dealing with Ado.Net components like Datatable, Dataset DataReader etc, through Entity , we can deal with real world objects like Custome, Supplier, Account.

2)    What are the main advantages of Entity Framework?

The main advantage of Entity Framework is that It generate code for Middle Layer, mapping code and Data Access code so it helps developers to reduce efforts and also increase productivity.

3)    What is .edmx file?

.edmx file is an xml file and It have the mapping of CSDL, MSL and SSDL as shown below

 4)    what is CSDL, MSL and SSDL in Entity framework?

 These are the main components of .edmx file

CSDL – Conceptual Schema Definition Language – It is an conceptual mdel which is directly exposed to Application

MSL – Mapping Schema Language – It connects or map CSDL and SSDL

SSDL – Storage Schema Definition Language - - It directly connect with Database and so takes care of RDMS related activity.

5)    Explain how to read records using Entity Framework classes?

For reading data from Entity framework , we have some steps

·         Create object of Context class

CustomerEntities ctxCustomer = new CustomerEntities();

·         Loop through the Context object

foreach (Customer ctxCustomer in obj.Customers)

{

 // get data for customer object

}

6)    Explain CRUD (Create Read Update Delete)  operation by Entity framework?

So just take a example of Customer that is having 2 field

Class Customer {

Public int CustomerId {get; set;}

Public string CustomerName {get; set;}

}

Add Operation – first create object of context class then create object of Customer Class , then add required information for customer and then add and Save through Entity via SaveChanges

CustomerEntities ctxCustomer = new CustomerEntities();

Customer objCust = new Customer();

objCust.CustomerId = 1

objCust.CustomerName = "Ramesh kumar";

ctxCustomer.Customers.AddObject(objCust);

ctxCustomer.SaveChanges();

Update Operation – For update just select particular Customer record and call AcceptAllChanges

CustomerEntities ctxCustomer = new CustomerEntities();

Customer objCust = ctxCustomer.Customers.Where(s=>s.CustomerId==1). FirstOrDefault();

objCust.CustomerName = "Ramesh ";

ctxCustomer.AcceptAllChanges ();

Delete Operation – For delete just select particular Customer record and call DeleteObject

CustomerEntities ctxCustomer = new CustomerEntities();

Customer objCust = ctxCustomer.Customers.Where(s=>s.CustomerId==1). FirstOrDefault();

objCust.CustomerName = "Ramesh ";

ctxCustomer.DeleteObject ();

7)    Explain pluralize and singularize in the Entity Framework and its importance ?

As per the English meaning of pluralize and singularize, we can easily know the meaning of these two but just connect to Entity and try to understand

Pluralize – shows Customer’s (means lot of customers)

singularize– shows Customer (means single  customers only)

So these are the naming conventions Entity Framework create it by Entity data model wizard.

8)    What are T4 Templates?

T4 template are the main component of Entity framework , It reads .edmx file that is in xml and generates code in C#.

9)    What is Lazy Loading and what is its behaviour in Entity Framework?

Lazy loading is the default behaviour of Entity lets understand it by example Suppose we have an table  Customer and Every customer have related to CustomerAddress table.

So as per entity first we have to get Customer Details from table via Entity and then loop through get Address from Customer table for each customer.

So the problem is that there are many un-relevant call to database ,

1) Getting customer data

2) Getting Address data and if for each customer 3 address are there then 3 more call to address for each customer

Below are the code through this, you can easily corelate it

CustomerEntities ctxCustomer = new CustomerEntities();

var Customers = ctxCustomer.Customers.ToList();

foreach (Customercust in Customers) // In this line no address object loaded

{

     foreach(Address add in cust.Addresses){}// Address object is loaded here

}

This is the big problem in Lazy loading.

10)  What is Eager Loading?

Eager Loading helps us to ignore Lazy loading or through this you can turn off Lazy loading and get all data in one go by using include keyword.

So How to Turn off Lazy loading

By calling below code you can turn off Lazy loading

context.ContextOptions.LazyLoadingEnabled = false;

How to Use Eager Loading

By calling below code you can we can use Eager loading, so now rather than calling many database hits , you can easily get data in one single database call.

var employees = context.Customers.Include("Addresses").Take(5);