Entity Framework - An Introduction

As per Microsoft defeinition, Entity Framework is an object-relational mapper (O/RM) that enables .NET developers to work with a database using .NET objects. It eliminates the need for most of the data-access code that developers usually need to write.

Entity Framework 6 (EF6) is a tried and tested data access technology with many years of features and stabilization. It first released in 2008, as part of .NET Framework 3.5 SP1 and Visual Studio 2008 SP1. Starting with the EF4.1 release it has shipped as the EntityFramework NuGet package - currently one of the most popular packages on NuGet.org.

Entity Framework allows you to create a database model by writing code or using boxes and lines in the EF Designer. Both of these approaches can be used to target an existing database or create a new database.

Another approach is to recreate the database model in Entity Framework designer by just fetching real schema entities from the database, and such this approach is called as Database-First approach. We shall bediscussing this approach in this article.

If you have an existing database and quite a number of database entities already defined in the database schema, and you would like to use this DB schema to create a model in your DOTNET program so that you could use the underneath database efficiently, EF comes to your assistance. It provides smooth operations of creation of the model from the database, creating corresponding data entities called as DOTNET entities that we can use easily in our program controllers and Server side code.
In the following sections, major steps in implementing Entity Framework database first approach, are discussed.

SQL-Database to Link Mapping

Creating an Entity Model

It introduces YourModel.edmx sub-folder, and within that another sub-folder YourModel.tt that contains multiple files with .cs extension. Each of these files represent an object that corresponds to the database table. A typical .cs file looks like the following: -

namespace YourProgram.Models
{
    using System;
    using System.Collections.Generic;
    
    public partial class LibraryBook
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public LibraryBook()
        {
            this.Bookmarks = new HashSet();
            this.Tags = new HashSet();
        }
    
        public int BookID { get; set; }
        public string Title { get; set; }
        public string TitleName { get; set; }
        public int SectionID { get; set; }
        public Nullable CategoryID { get; set; }
        public Nullable AuthorID { get; set; }
        public string BookFile { get; set; }
        public string BookBrief { get; set; }
        
        public virtual Category Category { get; set; }
        public virtual Section Section { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection Bookmarks { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection Tags { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
      
    }
}

The object structure is automatically built as per your schema in the database. Virtual properties and collections represent relations amongst tables etc with constraints.

Once the diagram is ready, you compile the program without any error(s), you are ready to use EF objects in your program through high level LINK language.