Entity Framework Core Overview

What is Entity Framework Core?

Entity Framework Core (EF Core) is a modern, cross-platform, extensible, and lightweight version of the popular Microsoft Entity Framework data access technology. It allows developers to work with a conceptual model, rather than the raw database structures, making data access more intuitive and less error-prone.

EF Core enables you to interact with your database using .NET objects, abstracting away the complexities of SQL and database-specific syntax. This promotes a more object-oriented approach to data persistence.

Key Features

Cross-Platform: Runs on Windows, macOS, and Linux.
Modern & Extensible: Designed for modern application development with a modular architecture.
Lightweight: Reduced dependencies and smaller footprint.
LINQ Support: Query your database using Language Integrated Query (LINQ).
Migrations: Manage database schema changes systematically.
Performance Improvements: Optimized for speed and efficiency.
Multiple Database Providers: Supports SQL Server, SQLite, PostgreSQL, MySQL, Cosmos DB, and more.

Getting Started

To start using EF Core, you'll typically need to install the necessary NuGet packages. The core package is Microsoft.EntityFrameworkCore. You'll also need a provider for your specific database.

For example, to add SQL Server support:

Install-Package Microsoft.EntityFrameworkCore.SqlServer

And to manage migrations:

Install-Package Microsoft.EntityFrameworkCore.Tools

Core Concepts

Understanding these core concepts is crucial for effective use of EF Core:

1. DbContext

The DbContext is the primary class for interacting with the database. It represents a session with the database and can be used to query and save data. You typically create a class that inherits from DbContext and includes DbSet<TEntity> properties for your entities.


public class BloggingContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }
    public DbSet<Post> Posts { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("YourConnectionString");
    }
}

2. DbSet<TEntity>

A DbSet<TEntity> represents a collection of a given entity type in the database. It's used to query and interact with tables.

3. Migrations

Migrations allow you to evolve your database schema over time as your application's data model changes. You can create a migration from your C# code model, and EF Core will generate the SQL to update your database.

To add a new migration:

Add-Migration InitialCreate

To apply migrations to the database:

Update-Database

4. Database Providers

EF Core uses providers to map its operations to the specific database system you are using. You must install and configure the appropriate provider for your database.

Querying Data

You can query data using LINQ. EF Core translates these LINQ queries into SQL that your database can understand.


using (var context = new BloggingContext())
{
    var blogs = context.Blogs
                       .Where(b => b.Rating > 3)
                       .OrderBy(b => b.Url)
                       .ToList();

    foreach (var blog in blogs)
    {
        Console.WriteLine($"Blog URL: {blog.Url}");
    }
}

Saving Data

To save data, you add, modify, or remove entities from your DbContext and then call SaveChanges().


using (var context = new BloggingContext())
{
    var newBlog = new Blog { Url = "http://example.com/blog", Rating = 5 };
    context.Blogs.Add(newBlog);
    context.SaveChanges();

    var existingBlog = context.Blogs.Find(1);
    if (existingBlog != null)
    {
        existingBlog.Rating = 4;
        context.SaveChanges();
    }
}