Events are not just for notifications Greg Young Qcon London Agenda - - PowerPoint PPT Presentation

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events are not just for notifications
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Events are not just for notifications Greg Young Qcon London Agenda - - PowerPoint PPT Presentation

Oct 28, 2022 30 likes •291 views

Events are not just for notifications Greg Young Qcon London Agenda Event Storage Testing With Events Versioning Performance Traveling Through Space and Time Let Everyone Run to Airport to Catch Flights Line Items (n) Purchase Order

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Events are not just for notifications

Greg Young Qcon London

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Agenda

Event Storage Testing With Events Versioning Performance Traveling Through Space and Time Let Everyone Run to Airport to Catch Flights

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Purchase Order Line Items (n) Shipping Information

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Cart Created Line Item Added Address Added Line Item Added Line Item Added

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Cart Created Line Item Added Address Added Line Item Added Line Item Added Cart Object

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Cart Created Line Item Added Address Added Line Item Added Line Item Added Line Item Removed Address Added

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Cart Created Line Item Added Address Added Line Item Added Line Item Added New Cart Object (Looks totally different)

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6 5 4 3 2 1 7

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5 snap 4 3 2 1 6

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Base { public IEnumerable<Event> GetUncommittedChanges() { return _changes; } public void MarkChangesAsCommitted() { _changes.Clear(); } public void LoadsFromHistory(IEnumerable<Event> history) { foreach (var e in history) ApplyChange(e, false); } }

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Base { protected void ApplyChange(Event @event) { ApplyChange(@event, true); } private void ApplyChange(Event @event, bool isNew) { this.AsDynamic().Apply(@event); if(isNew) _changes.Add(@event); } }

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private void Apply(InventoryItemDeactivated e) { _activated = false; } public void Deactivate() { if(!_activated) throw new InvalidOperationException("already deactivated"); ApplyChange(new InventoryItemDeactivated(_id)); }

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Derived { protected void ApplyChange(Event @event) { ApplyChange(@event, true); } private void ApplyChange(Event @event, bool isNew) { this.AsDynamic().Apply(@event); if(isNew) _changes.Add(@event); } }

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Overdraw attempts are rejected Given An account with $100 When A debit is requested for $101 Then An InsufficientBalanceException is thrown

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Overdraw attempts are rejected Given An account was created. An initial deposit was made for $100 When A debit is requested for $101 Then An InsufficientBalanceException is thrown

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Overdraw attempts are rejected Given A series of events When A command Then A series of events

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Not allowed to take money out of an overdrawn account Given An account was created. An initial deposit was made for $100 $100 was withdrawn When A debit is requested for $20 Then An InsufficientBalanceException is thrown

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Traveling Through Time.

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