Entity Framework: Database First Approach

Explore the Database First approach in Entity Framework, a powerful Object-Relational Mapper (ORM) for .NET. This approach allows you to generate your Entity Framework model directly from an existing database.

Overview

The Database First approach is ideal when you have an established database and want to leverage Entity Framework to interact with it. It automates the process of creating your data model (entity classes and the DbContext) based on your database schema.

When to Use Database First

• You are working with a legacy database.
• You have a database schema that is maintained independently of your application.
• You prefer to have full control over the database design.

Steps Involved

The general workflow for the Database First approach involves the following steps:

1. Connect to the Database: Establish a connection to your existing database.
2. Generate the Model: Use Visual Studio's Entity Data Model wizard to generate entity classes and a DbContext based on the database tables and views.
3. Configure the Connection String: Update the application's configuration file (e.g., App.config or Web.config) with the correct connection string.
4. Use the Model: Interact with your database using the generated entity classes and DbContext.

Generating the Entity Data Model (.edmx)

In Visual Studio:

1. Right-click on your project in Solution Explorer.
2. Select Add > New Item....
3. Search for "ADO.NET Entity Data Model" and select it.
4. Give your model a name (e.g., MyDatabaseModel.edmx).
5. In the "Entity Data Model" wizard, choose Database from existing database and click Next.
6. Configure your data connection or select an existing one. Ensure you select the correct database.
7. Choose the database objects (tables, views) you want to include in your model.
8. Click Finish.

This process generates an .edmx file, which contains the conceptual model, the storage model, and the mapping between them. It also generates your entity classes and the DbContext.

Example Usage

Once the model is generated, you can use it in your application like this:

using System.Linq;

// Assuming your DbContext is named YourDbContext and has a DbSet for Products
using (var context = new YourDbContext())
{
    // Retrieve all products
    var products = context.Products.ToList();

    foreach (var product in products)
    {
        Console.WriteLine($"Product ID: {product.ProductID}, Name: {product.Name}");
    }

    // Add a new product
    var newProduct = new Product
    {
        Name = "New Gadget",
        Price = 99.99m
    };
    context.Products.Add(newProduct);
    context.SaveChanges();

    Console.WriteLine("New product added.");
}
                

Entity Classes

The generated entity classes will typically look like this (simplified):

public class Product
{
    public int ProductID { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    // Other properties corresponding to database columns
}
                

DbContext Class

The generated DbContext class will have properties for each DbSet representing your tables:

using System.Data.Entity;

public partial class YourDbContext : DbContext
{
    public YourDbContext()
        : base("name=YourDbContext") // Name of your connection string in App.config/Web.config
    {
    }

    public virtual DbSet<Product> Products { get; set; }
    // Other DbSets for other tables

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }
}
                

Customizing the Model

You can customize the generated model by:

• Editing the .edmx file visually.
• Using the Model Designer to map tables, columns, and relationships.
• Using T4 templates to generate custom code.