Entity Framework Interview Preparation Guide

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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.

To simply say it: 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 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 maps to relational database objects (tables, views & storedprocedures). ORM helps us to keep our database design separate from our domain class design. This makes application maintainable and extendable. It also automates standard CRUD operation (Create, Read, Update & Delete) so developer doesn’t need to write it manually.

Entity framework has a full provider model. It supports not only SQL Server but also other database like Oracle, DB2, MySQL etc.

Most of the time L2S classes must be one-to-one with database objects e.g. Customer class can be mapped only with Customer table. Where as in Entity Framework you can map your domain class with multiple tables using various inheritance strategies like table per type (class) or table per hierarchy of classes etc.

You can have multiple modeling techniques using Entity Framework 4.1 like code first, model first or database first.

Microsoft has long term strategy to support and integrate Entity Framework with multiple Microsoft products.

EDM consist three main parts- Conceptual model, Mapping and Storage model.

Conceptual model is your model classes and their relationships. This will be independent from your database table design.

Storage model is your database design model which includes tables, views, stored procedures and their relationships and keys.

Mapping consist information about how your conceptual model is mapped to storage model.

LINQ to Entities is query language used to write queries against the object model. It returns entities which are defined in the conceptual model. You can use your LINQ skills here.

Entity SQL is again a query language same as LINQ to Entities. However it is little more difficult than L2E and also developer need to learn it separately.

Object service is a main entry point for accessing data from database and to return it back. Object service is responsible for materialization which is process of converting data returned from entity client data provider (next layer) to an entity object structure.

The main responsibility of this layer is to convert L2E or Entity SQL queries into SQL query which is understood by underlying database. It communicates with ADO.Net data provider which in turn sends or retrieves data from database.