What’s the difference between LINQ to SQL and Entity Framework?

The first big difference between the Entity Framework and LINQ to SQL is that the EF has a full provider model which means that as providers come online (and there are several in beta now and many which have committed to release within 3 months of the EF RTM), you will be able to use the EF against not only SQL Server and SQL CE but also Oracle, DB2, Informix, MySQL, Postgres, etc.

Next there is the fact that LINQ to SQL provides very limited mapping capabilities.  For the most part L2S classes must be one-to-one with the database (with the exception of one form of inheritance where there is a single table for all of the entity types in a hierarchy and a discriminator column which indicates which type a particular row represents).  In the case of the EF, there is a client-side view engine which can transform queries and updates made to the conceptual model into equivalent operations against the database.  The mapping system will produce those views for a variety of transformations.

 

Difference between POCO, Code First, and simple EF approach

All these three approaches define how much control you want on your Entity Framework code. Entity Framework is an OR mapper, it generates a lot of code, it creates your middle tier (Entity), and Data Access layer (Context).

But a lot of times you want to enjoy the benefits of both worlds, you want the auto-generation part to minimize your development time and you want control on the code so that you can maintain code quality.

Below is the difference table which defines each of the approaches. In simple Entity Framework, everything is auto generated and so you need the EDMX XML file as well. POCO is semi-automatic so you have full control on the entity classes but then the context classes are still generated by the EDMX file.

In Code First, you have complete control on how you can create the entity and context classes. Because you are going to manually create these classes, you do not have dependency on the EDMX XML file. Below is a simple table which shows the cross comparison.

	EDMX	Entity	Context
Simple entity framework	Needed	Auto	Auto
POCO approach	Needed	Manual	Auto
Code First	Not Needed	Manual	Manual

 

Lazy loading in a detailed manner – Entity Framework

By default EF has lazy loading behavior. Due to this default behavior if you are loading a large number of records and especially if they have foreign key relationships, you can have performance issues. So you need to be cautious if you really need lazy loading behavior for all scenarios. For better performance, disable lazy loading when you are loading a large number of records or use stored procedures.

Lazy loading is a concept where we load objects on demand rather than loading everything in one go. Consider a situation where you have 1 to many relationships between the Customer and Address objects. Now let’s say you are browsing the customer data but you do not want address data to be loaded at that moment. But the time you start accessing the address object you would like to load address data from the database.

Entity Framework has lazy loading behavior by default enabled. For instance, consider the below code. When we are doing a foreach on the Customer object, the Address object is not loaded. But the time you start doing foreach on the address collection, the Address object is loaded from SQL Server by firing SQL queries.

So in simple words, it will fire a separate query for each address record of the customer, which is definitely not good for a large number of records.

MyEntities context = new MyEntities();

var Customers = context.Customers.ToList();

foreach (Customercust in Customers) // In this line no address object loaded
{
     foreach(Address add in cust.Addresses){} // Address object is loaded here
}

 

CSDL, SSDL and MSL sections in an EDMX file

• CSDL (Conceptual Schema definition language) is the conceptual abstraction which is exposed to the application.
• SSDL (Storage Schema Definition Language) defines the mapping with your RDBMS data structure.
• MSL (Mapping Schema Language) connects the CSDL and SSDL.

CSDL, SSDL and MSL are actually XML files.

 

What is pluralize and singularize in the Entity Framework?

“Pluralize” and “Singularize” give meaningful naming conventions to objects. In simple words it says do you want to represent your objects with the below naming convention:

• One Customer record means “Customer” (singular).
• Lot of customer records means “Customer’s” (plural, watch the “s”)

 

What is Entity Framework?

Microsoft has given following definition:

The Microsoft ADO.NET Entity Framework is an Object/Relational Mapping (ORM) framework that enables developers to work with relational data as domain-specific objects, eliminating the need for most of the data access plumbing code that developers usually need to write. Using the Entity Framework, developers issue queries using LINQ, then retrieve and manipulate data as strongly typed objects. The Entity Framework’s ORM implementation provides services like change tracking, identity resolution, lazy loading, and query translation so that developers can focus on their application-specific business logic rather than the data access fundamentals.

Or simply: Entity framework is an Object/Relational Mapping (O/RM) framework. It is an enhancement to ADO.NET that gives developers an automated mechanism for accessing & storing the data in the database, and for working with the results, in addition to DataReader and DataSet.

Now the question is what is O/RM framework and why do we need it?

ORM is a tool for storing data from domain objects to relational database like MS SQL Server, in an automated way, without much programming. O/RM includes three main parts: Domain class objects, Relational database objects and Mapping information on how domain objects map to relational database objects (tables, views & storedprocedures). ORM allows us to keep our database design separate from our domain class design. This makes the application maintainable and extendable. It also automates standard CRUD operation (Create, Read, Update & Delete) so that the developer doesn’t need to write it manually.

Visit wikipedia for more information on Object-relational Mapping

There are many ORM frameworks for .net in the market like DataObjects.Net, NHibernate, OpenAccess, SubSonic etc. Entity Framework is an open source ORM framework from Microsoft.