Get Started with EF Core - .NET Documentation

Get Started with Entity Framework Core

Entity Framework Core (EF Core) is a modern object-relational mapper (ORM) for .NET that allows developers to work with databases using .NET objects and LINQ. It eliminates the need for most of the data-access code that developers traditionally need to write.

1. Installation

To get started, you'll need to install the necessary EF Core NuGet packages. The most common ones are:

dotnet add package Microsoft.EntityFrameworkCore

If you are using a specific database provider, install its corresponding package:

SQL Server: dotnet add package Microsoft.EntityFrameworkCore.SqlServer
SQLite: dotnet add package Microsoft.EntityFrameworkCore.Sqlite
Npgsql (PostgreSQL): dotnet add package Npgsql.EntityFrameworkCore.PostgreSQL
MySQL: dotnet add package MySql.EntityFrameworkCore

For tooling support (like migrations), you'll also need:

dotnet add package Microsoft.EntityFrameworkCore.Tools

2. Creating Your First Model and Context

EF Core works by mapping your .NET classes (entities) to database tables. You define these entities and then create a DbContext class to represent your database session.

Example Entity:

                
public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
    public List<Post> Posts { get; set; }
}

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; }
}
                
            

Example DbContext:

                
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)
    {
        // Replace with your actual connection string
        optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=BloggingEFCore;Trusted_Connection=True;");
    }
}
                
            

Tip: The DbContextOptionsBuilder can also be configured using dependency injection in ASP.NET Core applications, which is the recommended approach.

3. Core Concepts

Migrations

Migrations are a way to incrementally update your database schema to match your EF Core model. EF Core can generate SQL scripts to perform these updates.

To add a new migration:

dotnet ef migrations add InitialCreate

To apply the migration to your database:

dotnet ef database update

Migrations are crucial for managing database changes over time in a consistent and reproducible manner.

Queries

You can query your data using LINQ to Objects syntax. EF Core translates these LINQ queries into SQL.

                
using var db = new BloggingContext();

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

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

Relationships

EF Core supports various relationships, including one-to-many and many-to-many. The example above shows a one-to-many relationship between Blog and Post.

You can configure relationships more explicitly in the OnModelCreating method of your DbContext if needed.

4. Advanced Topics

EF Core offers a rich set of features for more complex scenarios, including:

5. API Reference

For a comprehensive list of EF Core classes and methods, please refer to the official .NET API Browser.

This guide provides a basic introduction. For detailed information and more advanced scenarios, consult the full EF Core documentation.