Object-Relational Mapping (ORM) bridges the gap between object-oriented code and relational databases.

Key components include:

• Model: Defines the data structure.
• Context: Acts as an in-memory database, allowing CRUD operations.
• Mappings: Specifies relationships between classes and database tables.

Working of the Entity Framework

• Model First: Design the model, then generate the database.
• Database First: Use an existing database to generate a model.
• Code First: Define classes and relationships first, then generate a database.

Core Concepts of EF

• DbContext: Represents a session with the database.

• Entity: An object that you map to a table or a view in the database.

• DbSet<T>: Represents a table or a view.

• Entity State: Describes the state of an entity in the context.

  • Added
  • Modified
  • Deleted
  • Detached
  • Unchanged

• Query: Describes how data is retrieved through LINQ.

Coordination Between Database and Objects

• Change Tracking: Records modifications made to entity objects during their lifecycle.

• Relationship Management: Manages relational data by using techniques like lazy loading, eager loading, and explicit loading.

• Transaction Management: Handles unit of work operations within the database.

• Caching: Maintains an in-memory state of entities for enhanced performance.

Code Example: Entity Framework

Here is the Csharp code:

// Define the model
public class Customer {
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection<Order> Orders { get; } = new List<Order>();
}

public class Order {
    public int Id { get; set; }
    public decimal Amount { get; set; }
}

// Define the context
public class MyDbContext : DbContext {
    public DbSet<Customer> Customers { get; set; }
    public DbSet<Order> Orders { get; set; }
}

// Usage
using (var context = new MyDbContext()) {
    // Insert
    var customer = new Customer { Name = "John Doe" };
    context.Customers.Add(customer);

    // Query
    var customersWithOrders = context.Customers.Include(c => c.Orders).ToList();

    // Update
    customer.Name = "Jane Doe";

    // Remove
    context.Customers.Remove(customer);

    // Save changes
    context.SaveChanges();
}