Explain the principles of operation and main features of Entity Framework Core as an ORM tool for .NET applications.

Entity Framework Core (EF Core) is an ORM (Object-Relational Mapper) for .NET that allows working with a database through objects and classes without directly using SQL queries.

Main features of EF Core:

• Support for LINQ to write database queries in C#.
• Change tracking of objects and automatic generation of SQL commands for database updates.
• Migrations — a mechanism for managing database schema changes.
• Cross-platform support and compatibility with various DBMS (SQL Server, SQLite, PostgreSQL, etc.).

Working principle:

1. Define model classes that correspond to tables.
2. Create a data context (DbContext) that manages the connection and objects.
3. Use LINQ queries for selecting, adding, updating, and deleting data.

Example:

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class AppDbContext : DbContext
{
    public DbSet<Product> Products { get; set; }
}

using(var context = new AppDbContext())
{
    var products = context.Products.Where(p => p.Name.Contains("book")).ToList();
}