EventSourcing.NetCore

 public record Person (
    string Name ,
    string Address
) ;

public record InvoiceInitiated (
    double Amount ,
    string Number ,
    Person IssuedTo ,
    DateTime InitiatedAt
) ;

public record InvoiceIssued (
    string IssuedBy ,
    DateTime IssuedAt
) ;

public enum InvoiceSendMethod
{
    Email ,
    Post
}

public record InvoiceSent (
    InvoiceSendMethod SentVia ,
    DateTime SentAt
) ;

public enum InvoiceStatus
{
    Initiated = 1 ,
    Issued = 2 ,
    Sent = 3
}

public class Invoice
{
    public string Id { get ; set ; }
    public double Amount { get ; private set ; }
    public string Number { get ; private set ; }

    public InvoiceStatus Status { get ; private set ; }

    public Person IssuedTo { get ; private set ; }
    public DateTime InitiatedAt { get ; private set ; }

    public string IssuedBy { get ; private set ; }
    public DateTime IssuedAt { get ; private set ; }

    public InvoiceSendMethod SentVia { get ; private set ; }
    public DateTime SentAt { get ; private set ; }

    public void Evolve ( object @event )
    {
        switch ( @event )
        {
            case InvoiceInitiated invoiceInitiated :
                Apply ( invoiceInitiated ) ;
                break ;
            case InvoiceIssued invoiceIssued :
                Apply ( invoiceIssued ) ;
                break ;
            case InvoiceSent invoiceSent :
                Apply ( invoiceSent ) ;
                break ;
        }
    }

    private void Apply ( InvoiceInitiated @event )
    {
        Id = @event . Number ;
        Amount = @event . Amount ;
        Number = @event . Number ;
        IssuedTo = @event . IssuedTo ;
        InitiatedAt = @event . InitiatedAt ;
        Status = InvoiceStatus . Initiated ;
    }

    private void Apply ( InvoiceIssued @event )
    {
        IssuedBy = @event . IssuedBy ;
        IssuedAt = @event . IssuedAt ;
        Status = InvoiceStatus . Issued ;
    }

    private void Apply ( InvoiceSent @event )
    {
        SentVia = @event . SentVia ;
        SentAt = @event . SentAt ;
        Status = InvoiceStatus . Sent ;
    }
}

 var invoiceInitiated = new InvoiceInitiated (
    34.12 ,
    "INV/2021/11/01" ,
    new Person ( "Oscar the Grouch" , "123 Sesame Street" ) ,
    DateTime . UtcNow
) ;
var invoiceIssued = new InvoiceIssued (
    "Cookie Monster" ,
    DateTime . UtcNow
) ;
var invoiceSent = new InvoiceSent (
    InvoiceSendMethod . Email ,
    DateTime . UtcNow
) ;

// 1,2. Get all events and sort them in the order of appearance
var events = new object [ ] { invoiceInitiated , invoiceIssued , invoiceSent } ;

// 3. Construct empty Invoice object
var invoice = new Invoice ( ) ;

// 4. Apply each event on the entity.
foreach ( var @event in events )
{
    invoice . Evolve ( @event ) ;
}

 public abstract class Aggregate < T >
{
    public T Id { get ; protected set ; }

    protected Aggregate ( ) { }

    public virtual void Evolve ( object @event ) { }
}

 var reservationId = "RES/01" ;
var seatId = "SEAT/22" ;
var customerId = "CUS/291" ;

var reservation = new Reservation (
    reservationId ,
    seatId ,
    customerId
) ;

 var reservationId = new ReservationId ( "RES/01" ) ;
var seatId = new SeatId ( "SEAT/22" ) ;
var customerId = new CustomerId ( "CUS/291" ) ;

var reservation = new Reservation (
    reservationId ,
    seatId ,
    customerId
) ;

 public class StronglyTypedValue < T > : IEquatable < StronglyTypedValue < T > > where T : IComparable < T >
{
    public T Value { get ; }

    public StronglyTypedValue ( T value )
    {
        Value = value ;
    }

    public bool Equals ( StronglyTypedValue < T > ? other )
    {
        if ( ReferenceEquals ( null , other ) ) return false ;
        if ( ReferenceEquals ( this , other ) ) return true ;
        return EqualityComparer < T > . Default . Equals ( Value , other . Value ) ;
    }

    public override bool Equals ( object ? obj )
    {
        if ( ReferenceEquals ( null , obj ) ) return false ;
        if ( ReferenceEquals ( this , obj ) ) return true ;
        if ( obj . GetType ( ) != this . GetType ( ) ) return false ;
        return Equals ( ( StronglyTypedValue < T > ) obj ) ;
    }

    public override int GetHashCode ( )
    {
        return EqualityComparer < T > . Default . GetHashCode ( Value ) ;
    }

    public static bool operator == ( StronglyTypedValue < T > ? left , StronglyTypedValue < T > ? right )
    {
        return Equals ( left , right ) ;
    }

    public static bool operator != ( StronglyTypedValue < T > ? left , StronglyTypedValue < T > ? right )
    {
        return ! Equals ( left , right ) ;
    }
}

 public class ReservationId : StronglyTypedValue < Guid >
{
    public ReservationId ( Guid value ) : base ( value )
    {
    }
}

 public class ReservationNumber : StronglyTypedValue < string >
{
    public ReservationNumber ( string value ) : base ( value )
    {
        if ( string . IsNullOrEmpty ( value ) || ! value . StartsWith ( "RES/" ) || value . Length <= 4 )
            throw new ArgumentOutOfRangeException ( nameof ( value ) ) ;
    }
}

 public abstract class Aggregate < TKey , T >
    where TKey : StronglyTypedValue < T >
    where T : IComparable < T >
{
    public TKey Id { get ; set ; } = default ! ;

    [ Identity ]
    public T AggregateId    {
        get => Id . Value ;
        set { }
    }

    public int Version { get ; protected set ; }

    [ JsonIgnore ] private readonly Queue < object > uncommittedEvents = new ( ) ;

    public object [ ] DequeueUncommittedEvents ( )
    {
        var dequeuedEvents = uncommittedEvents . ToArray ( ) ;

        uncommittedEvents . Clear ( ) ;

        return dequeuedEvents ;
    }

    protected void Enqueue ( object @event )
    {
        uncommittedEvents . Enqueue ( @event ) ;
    }
}

 public class Reservation : Aggregate < ReservationId , Guid >
{
    public CustomerId CustomerId { get ; private set ; } = default ! ;

    public SeatId SeatId { get ; private set ; } = default ! ;

    public ReservationNumber Number { get ; private set ; } = default ! ;

    public ReservationStatus Status { get ; private set ; }

    public static Reservation CreateTentative (
        SeatId seatId ,
        CustomerId customerId )
    {
        return new Reservation (
            new ReservationId ( Guid . NewGuid ( ) ) ,
            seatId ,
            customerId ,
            new ReservationNumber ( Guid . NewGuid ( ) . ToString ( ) )
        ) ;
    }

    // (...)
}