Entity Framework Core Basics

Entity Framework Core (EF Core) is a modern object-relational mapper (ORM) for .NET. It enables .NET developers to work with a database using .NET objects that map to the database schema. It eliminates the need for most of the data-access code that developers need to write.

What is an ORM?

An Object-Relational Mapper (ORM) is a type of middleware that is used to convert data between incompatible type systems within object-oriented programming languages. It bridges the gap between your object-oriented code and a relational database.

Key Concepts in EF Core

1. DbContext

The DbContext is the primary class used when interacting with EF Core. It represents a session with the database and allows you to query and save data. You typically create a class that inherits from DbContext and add DbSet<TEntity> properties for each entity in your model.

using Microsoft.EntityFrameworkCore;

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

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=Blogging;Trusted_Connection=True;");
    }
}

2. Entities

Entities are plain old CLR objects (POCOs) that represent tables in your database. EF Core maps these objects to database tables. Properties on entity classes map to columns in the database.

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
    public ICollection<Post> Posts { get; } = new List<Post>();
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public int BlogId { get; set; }
    public Blog Blog { get; set; }
}

3. DbSet

A DbSet<TEntity> represents a collection of all entities in the store for a given type. Think of it as a table in your database. You use DbSet properties on your DbContext to access and manipulate entities.

Common Operations

Creating the Database (Migrations)

EF Core uses Migrations to incrementally update your database schema as your domain model changes. This process involves generating migration files that contain C# code to describe the changes.

To enable Migrations, you'll typically install the EF Core tools:

dotnet tool install --global dotnet-ef

Then, you can add your first migration:

dotnet ef migrations add InitialCreate
dotnet ef database update

Querying Data

You can query data by accessing the DbSet on your DbContext and using LINQ (Language Integrated Query).

using var db = new BloggingContext();

var blogs = db.Blogs
              .Where(b => b.Url.Contains("example.com"))
              .OrderBy(b => b.Url);

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

Adding Data

To add new entities, you create instances of your entity classes and add them to the appropriate DbSet.

using var db = new BloggingContext();

var newBlog = new Blog { Url = "http://newblog.example.com" };
db.Blogs.Add(newBlog);
db.SaveChanges(); // Persist changes to the database

Updating Data

To update an entity, retrieve it from the database, modify its properties, and then call SaveChanges().

using var db = new BloggingContext();

var blogToUpdate = db.Blogs.FirstOrDefault(b => b.Url == "http://newblog.example.com");
if (blogToUpdate != null)
{
    blogToUpdate.Url = "http://updatedblog.example.com";
    db.SaveChanges();
}

Deleting Data

To delete an entity, retrieve it from the database and then call Remove() on the DbSet.

using var db = new BloggingContext();

var blogToDelete = db.Blogs.FirstOrDefault(b => b.Url == "http://updatedblog.example.com");
if (blogToDelete != null)
{
    db.Blogs.Remove(blogToDelete);
    db.SaveChanges();
}

Next Steps

This section covered the fundamental concepts of EF Core. For more advanced topics like relationships, complex queries, and performance optimization, please refer to the other documentation sections.

• EF Core Migrations
• Querying Data with EF Core
• Defining Relationships