Using Code First in Entity Framework

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Introduction

Generally, entity framework is majorly used by adding an edmx file into your .Net solution and creating tables or dropping tables from existing SQL database. But in certain cases when we are working on large scale applications and having layered architecture with different layers (presentation, service, business and data access) it becomes quite difficult for the developer to make it loosely coupled.

In order to explain, let’s take a simple scenario. Let suppose you have a Web Application with following layers

  1. Web Front End ( ASP.Net MVC)
  2. Service Layer (WCF, Web Services)
  3. Business Layer (Business Managers)
  4. Data Access Layer (Entity Framework)

Web Front End use some models that are bean classes to store data and transmit them the Service layer, service layers are expecting Data Contracts to be passed as parameters and Business Layers actually processes that data and passes it to Data Access Layer to perform to and fro CRUD operations.

Problem

We can make common library project that contains single bean which can be travel from presentation layer to Services and Services to Business layer. Problem arises when we need to pass it to the entity framework. As if we are not using a code first approach we need to map that class to appropriate entity framework entity class. This will increase performance decline and also increase extra effort for developer to provide mappings for all the entities.

Resolution

When you use Code First model you really don’t need to include edmx file into your solution, and you just have to define bean classes or entity classes for each table creating or created already. This helps to place all the classes in one common library that will be referenced by all and will support loosely coupling of layers.

Steps

Steps to Create Entity Framework Code First Model

  1. Create a new Project named as CommonEntities
  2. Add a Library Package Reference of EFCodeFirst using NuGet

  3. Create a new folder named as “Entities” inside your project and define all the entities. Entities contain setter getter properties for all the columns in a table.

For e.g. here are the sample classes


public
class
DocumentColumns

{

[Key]


public
Int32 ColumnId { get; set; }


public
String ColumnName { get; set; }


public
String ColumnType { get; set; }


public
Int32 TypeSize { get; set; }


public
Boolean IsPrimary { get; set; }


public
Boolean AllowNulls { get; set; }


public
Boolean IsMeasure { get; set; }


public
Int32 DocumentId { get; set; }


public
String ColumnSheets { get; set; }

}


public
class
Document

{

[Key]


public
Int32 DocumentId { get; set; }


public
String DocumentPath { get; set; }


public
String DocumentName { get; set; }


public
String DocumentDescription { get; set; }


public
String TableName { get; set; }


public
Boolean IsActive { get; set; }


public
Boolean IsStarSchema { get; set; }


public
String DatabaseName { get; set; }


public
ICollection<DocumentColumns> DocumentColumns { get; set; }

}

Attribute [Key] denotes that particular property is a primary key.

  1. Create a custom context class named as “MyDbContext” which should be derived from System.Data.Entity.DbContext

    public
    class
    SchedulerContext : System.Data.Entity.DbContext

    {


    public
    DbSet<Document> Documents { get; set; }


    public
    DbSet<DocumentColumns> DocumentColumns { get; set; }


    protected
    override
    void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder)

    {

    modelBuilder.IncludeMetadataInDatabase = false;

    }

    }

Here in the above snippet I have overridden the OnModelCreating method and set IncludeMetadataInDatabase = false, this basically not create a new database. This is normally used when you have already an existing database created and you don’t want Entity Framework to create a new database for you.

  1. Add the App.config file in your project and specify the Connectionstring as follows

<connectionStrings>

<add
name=“ExcelScheduler.Database.SchedulerContext”


connectionString=“Data Source=.\sqlexpress;Initial Catalog=SchedulerDB;Integrated Security=True”


providerName=“System.Data.SqlClient“ />

</connectionStrings>

This is all done!

Now in order the treat any entity class as WCF data contract you just need to annotate your entity class with [DataContract] attribute and properties with [DataMember] attribute. And same goes if you want to use it with Asp.Net MVC models.

104 thoughts on “Using Code First in Entity Framework”

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