Entity Framework Overview

Entity Framework (EF) is a set of data access technologies for .NET that enables developers to work with data using domain-specific objects instead of directly interacting with storage-dependent query languages such as T-SQL. EF abstracts away the need for data access plumbing that developers usually need to implement.

What is Entity Framework?

Entity Framework is an Object-Relational Mapper (ORM). It allows you to define your data model using .NET classes, and EF handles the mapping between these classes and your database tables. This means you can query and manipulate data using familiar C# or VB.NET code, without having to write explicit SQL statements for most common operations.

Key Benefits:

• Productivity: Reduces the amount of boilerplate data access code you need to write.
• Maintainability: Makes your code easier to read, understand, and maintain.
• Abstraction: Hides the complexities of the underlying database and SQL.
• Type Safety: Leverages .NET's type system for data operations, reducing runtime errors.
• Database Agnosticism: Can work with various database providers (SQL Server, PostgreSQL, MySQL, SQLite, etc.).

Core Concepts

Entity Framework revolves around several core concepts:

1. DbContext

The DbContext is the primary gateway to interacting with the data. It represents a session with the database and is used to query, insert, update, and delete data. It also tracks changes to entities.

using (var context = new MyDbContext())
{
    var products = context.Products.Where(p => p.Price > 50).ToList();
    // ...
}
            

2. DbSet

A DbSet<TEntity> represents a collection of all entities in the context, or that can be queried from the database, of a given type. You typically access a DbSet<TEntity> through the DbContext.DbSet<TEntity> property.

public class MyDbContext : DbContext
{
    public DbSet<Product> Products { get; set; }
    public DbSet<Category> Categories { get; set; }
}
            

3. Entities

Entities are .NET classes that represent tables in your database. They are simple POCO (Plain Old CLR Object) classes that map to database tables.

public class Product
{
    public int ProductId { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    public int CategoryId { get; set; }
    public Category Category { get; set; }
}
            

4. Migrations

Entity Framework Migrations is a feature that allows you to evolve your database schema over time as your application code changes. It helps you manage schema changes in a versioned way.

Ways to Use Entity Framework

EF supports several development patterns:

1. Code-First

In the Code-First approach, you start by writing your .NET classes (entities) and defining your context. EF then generates the database schema based on your code.

2. Database-First

With Database-First, you start with an existing database. EF can generate an entity model and DbContext from the database schema.

3. Model-First

Model-First involves designing your conceptual model in a visual designer. EF can then generate the database schema and the entity classes from this model.

Entity Framework Core vs. EF6

Entity Framework has evolved significantly. Entity Framework Core (EF Core) is the latest generation, designed for cross-platform use and improved performance. EF6 is the older, mature version primarily for Windows. While they share many concepts, there are differences in features and APIs.