Primary Constructor

Introduced in C# 12, primary constructors allow you to declare constructor parameters directly on the class or struct declaration, significantly reducing boilerplate code.

Abstract

Clean up your service classes and command handlers by declaring dependencies directly on the class signature: public class CreateOrderCommandHandler(IOrderRepository repository, ILogger<CreateOrderCommandHandler> logger)

Syntax Comparison

Primary Constructor (Modern C# 12+)

public class GameStoreContext(DbContextOptions<GameStoreContext> options) : DbContext(options)
{
    // Class members can directly use 'options' here
}

Classical Equivalent

public class GameStoreContext : DbContext
{
    public GameStoreContext(DbContextOptions<GameStoreContext> options) : base(options)
    {
    }
}

Key Characteristics

• Scope: Parameters defined in the primary constructor header are in scope for the entire class body.

• Field Capture (Classes vs. Records):

  • In record types, primary constructor parameters automatically become public init-only properties.

  • In standard class types, they remain parameters (not properties), but the compiler will automatically capture them into private backing fields if they are accessed within methods or properties inside the class.

• Base Class Chaining: You can pass parameters directly to a base class constructor using syntax like : BaseClass(paramName).

  public class Person(string name)
  {
      public string Name { get; } = name;
  }
   
  public class Employee(string name, string employeeId) : Person(name)
  {
      public string EmployeeId { get; } = employeeId;
  }

In this example, the Employee class uses a primary constructor to accept both name and employeeId. It immediately forwards the name parameter up to the base Person class constructor using : Person(name), while retaining employeeId for its own use.

Common EF Core Usage This pattern is widely adopted in Entity Framework Core for clean, minimal DbContext declarations without redundant constructor bodies.