The document discusses implementing CQRS and event sourcing patterns using RavenDB for persistence. It begins with an example employee management prototype and identifies issues with the initial approach. It then explores improving the model by defining commands, events, and having entities generate events in response to commands. Events are stored in RavenDB to rebuild entity state and allow queries to be answered from the event stream. The document provides examples of handling commands, generating and applying events, and saving events to documents in RavenDB.

1. CQRS e Event Sourcing na
prática com RavenDB
Elemar Júnior
@elemarjr
elemarjr@ravendb.net
elemarjr@gmail.com
elemarjr.com

2. Olá, eu sou Elemar Jr

3. Eu sou Microsoft MVP

4. Eu gosto de aprender coisas novas

5. Eu gosto de resolver problemas

6. Eu gosto de escrever compiladores

7. Eu gosto do
Roslyn (e do
CoddeCracker)

8. Eu gosto de
Computação Gráfica

9. Eu gosto de
Heurísticas

10. Eu gosto de
RavenDB

11. CQRS e Event Sourcing na prática
com RavenDB
Mas, vamos falar de

12. Vamos pensar em um cenário...

13. Precisamos criar um um cadastro
de funcionários...

14. Coisa simples...
Nome, Endereço Residencial e Salário

15. Começamos com um protótipo

16. [Route("api/[controller]")]
public class EmployeesController : Controller
{
[HttpGet]
public IEnumerable<Employee> Get()
{ /* .. */ }
[HttpGet("{id}")]
public Employee Get(string id)
{ /* .. */ }
[HttpPost]
public void Post([FromBody]Employee value)
{ /* .. */ }
[HttpPut("{id}")]
public void Put(string id, [FromBody]Employee value)
{ /* .. */ }
[HttpDelete("{id}")]
public void Delete(string id)
{ /* .. */}
}
Podemos modelar
uma API...

17. public class Employee
{
public string Id { get; set; }
public string Name { get; set; }
public Address HomeAddress { get; set; }
public decimal Salary { get; set; }
}
Definir o Modelo
[Route("api/[controller]")]
public class EmployeesController : Controller
{
[HttpGet]
public IEnumerable<Employee> Get()
{ /* .. */ }
[HttpGet("{id}")]
public Employee Get(string id)
{ /* .. */ }
[HttpPost]
public void Post([FromBody]Employee value)
{ /* .. */ }
[HttpPut("{id}")]
public void Put(string id, [FromBody]Employee value)
{ /* .. */ }
[HttpDelete("{id}")]
public void Delete(string id)
{ /* .. */}
}

18. public class EmployeesRepository
{
public Employee Load(string id)
{
using (var session = DocumentStoreHolder.Instance.OpenSession())
{
return session.Load<Employee>(id);
}
}
public void Save(Employee newEmployee)
{
using (var session = DocumentStoreHolder.Instance.OpenSession())
{
session.Store(newEmployee);
session.SaveChanges();
}
}
}
Implementar persistência....

19. Pronto!

20. Será que ficou bom?

21. Vejamos...

22. UI (HTML + Angular)
WebAPI
RavenDB
Presentation
Business
Persistence

23. Esse modelo não está anêmico?
public class Employee
{
public string Id { get; set; }
public string Name { get; set; }
public Address HomeAddress { get; set; }
public decimal Salary { get; set; }
}

24. Cadê a linguagem ubíqua?
[Route("api/[controller]")]
public class EmployeesController : Controller
{
[HttpGet]
public IEnumerable<Employee> Get()
{ /* .. */ }
[HttpGet("{id}")]
public Employee Get(string id)
{ /* .. */ }
[HttpPost]
public void Post([FromBody]Employee value)
{ /* .. */ }
[HttpPut("{id}")]
public void Put(string id, [FromBody]Employee value)
{ /* .. */ }
[HttpDelete("{id}")]
public void Delete(string id)
{ /* .. */}
}

25. Será que escala?

26. Será que é fácil de alterar?

27. Vamos tentar resgatar conceitos...

31. ViewModel
InputModel

33. Modelo expressa o domínio
public sealed class Employee
{
public Guid Id { get; private set; }
public FullName Name { get; private set; }
public decimal Salary { get; private set; }
public Address HomeAddress { get; private set; }
public Employee(Guid id, FullName name, decimal initialSalary)
{ /* .. */ }
public void RaiseSalary(decimal amount)
{ /* .. */ }
public void ChangeHomeAddress(Address address)
{ /* .. */ }
}

34. Modelo expressa o domínio
public sealed class Employee
{
public Guid Id { get; private set; }
public FullName Name { get; private set; }
public decimal Salary { get; private set; }
public Address HomeAddress { get; private set; }
public Employee(Guid id, FullName name, decimal initialSalary)
{ /* .. */ }
public void RaiseSalary(decimal amount)
{ /* .. */ }
public void ChangeHomeAddress(Address address)
{ /* .. */ }
}

35. Modelo expressa o domínio
public sealed class Employee
{
public Guid Id { get; private set; }
public FullName Name { get; private set; }
public decimal Salary { get; private set; }
public Address HomeAddress { get; private set; }
public Employee(Guid id, FullName name, decimal initialSalary)
{ /* .. */ }
public void RaiseSalary(decimal amount)
{ /* .. */ }
public void ChangeHomeAddress(Address address)
{ /* .. */ }
}

36. Consolidação da Linguagem
Ubíqua
public sealed class Employee
{
public Guid Id { get; private set; }
public FullName Name { get; private set; }
public decimal Salary { get; private set; }
public Address HomeAddress { get; private set; }
public Employee(Guid id, FullName name, decimal initialSalary)
{ /* .. */ }
public void RaiseSalary(decimal amount)
{ /* .. */ }
public void ChangeHomeAddress(Address address)
{ /* .. */ }
}

37. Voltando ao protótipo...
public Employee(Guid id, FullName name, decimal initialSalary)
{ /* .. */ }

38. public sealed class Employee
{
public Guid Id { get; private set; }
public FullName Name { get; private set; }
public decimal Salary { get; private set; }
public Address HomeAddress { get; private set; }
public Employee(Guid id, FullName name, decimal initialSalary)
{ /* .. */ }
public void RaiseSalary(decimal amount)
{ /* .. */ }
public void ChangeHomeAddress(Address address)
{ /* .. */ }
}
Consolidação da Linguagem
Ubíqua

39. Cadê o protótipo?
public void RaiseSalary(decimal amount)
{ /* .. */ }

40. Command
InputModel

41. Anatomia de um Comando
public sealed class UpdateEmployeeHomeAddressCommand :
EmployeeCommand
{
public Address HomeAddress { get; }
public UpdateEmployeeHomeAddressCommand(
EmployeeId id,
Address address) : base(id)
{
HomeAddress = address;
}
}

42. Command
InputModel

43. public class EmployeeCommandsHandler : IMessageHandler<RegisterEmployeeCommand>,
IMessageHandler<RaiseSalaryCommand>, IMessageHandler<ChangeHomeAddressCommand>
{
private readonly IEmployeeRepository _repository;
public EmployeeCommandsHandler(IEmployeeRepository repository)
{ _repository = repository; }
public void Handle(RegisterEmployeeCommand command)
{
var newEmployee = new Employee(command.Id, command.Name, command.InitialSalary);
_repository.Save(newEmployee);
}
public void Handle(RaiseSalaryCommand command)
{
var employee = _repository.Load(command.EmployeeId);
employee.RaiseSalary(command.Amount);
_repository.Save(employee);
}
public void Handle(ChangeHomeAddressCommand command)
{
var employee = _repository.Load(command.EmployeeId);
employee.ChangeHomeAddress(command.NewAddress);
_repository.Save(employee);
}
}

46. InputModel
Command

47. Chegamos ao Manifesto Reativo

48. Resolvemos comandos! O que
fazemos com consultas

49. Vamos lembrar...

50. ViewModel

51. Logo, seria natural...

54. E isso é CQRS

55. ... mas e Event Sourcing?

56. Employee
RaiseSalaryCommand
SalaryRaisedEvent

57. Command
InputModel

58. Anatomia de um Evento
public class EmployeeHomeAddressChangedEvent
: VersionedEvent<Guid>
{
public Address NewAddress { get; }
public EmployeeHomeAddressChangedEvent(Address newAddress)
{
NewAddress = newAddress;
}
}
public class VersionedEvent<TSourceId> : IVersionedEvent<TSourceId>
{
public TSourceId SourceId { get; internal set; }
public DateTime When { get; private set; }
public int Version { get; internal set; }
public VersionedEvent()
{
When = DateTime.Now;
}
}

59. Anatomia de um Evento
public class EmployeeHomeAddressChangedEvent
: VersionedEvent<Guid>
{
public Address NewAddress { get; }
public EmployeeHomeAddressChangedEvent(Address newAddress)
{
NewAddress = newAddress;
}
}
public class VersionedEvent<TSourceId> : IVersionedEvent<TSourceId>
{
public TSourceId SourceId { get; internal set; }
public DateTime When { get; private set; }
public int Version { get; internal set; }
public VersionedEvent()
{
When = DateTime.Now;
}
}

60. Anatomia de um Evento
public class EmployeeHomeAddressChangedEvent
: VersionedEvent<Guid>
{
public Address NewAddress { get; }
public EmployeeHomeAddressChangedEvent(Address newAddress)
{
NewAddress = newAddress;
}
}
public class VersionedEvent<TSourceId> : IVersionedEvent<TSourceId>
{
public TSourceId SourceId { get; internal set; }
public DateTime When { get; private set; }
public int Version { get; internal set; }
public VersionedEvent()
{
When = DateTime.Now;
}
}

61. Stream de Eventos
EmployeeRegistered
HomeAddressUpdated
SalaryRaised
SalaryRaised
HomeAddressUpdated
SalaryRaised

62. Stream de Eventos
EmployeeRegistered
HomeAddressUpdated
SalaryRaised
SalaryRaised
HomeAddressUpdated
SalaryRaised
Por que não salvar?

63. Stream de Eventos
No RavenDB é fácil!

64. Stream de Eventos
No RavenDB é fácil!

65. ... mas antes é preciso
Gerar os Eventos

66. Entidade/Agregado gera Eventos
public Employee(Guid id, FullName name, decimal initialSalary)
: this(id)
{
Throw.IfArgumentIsNull(name, nameof(name));
Throw.IfArgumentIsNegative(initialSalary, nameof(initialSalary));
Update(new EmployeeRegisteredEvent(name, initialSalary));
}

67. Entidade/Agregado gera Eventos
public void RaiseSalary(decimal amount)
{
Throw.IfArgumentIsNegative(amount, nameof(amount));
Update(new EmployeeSalaryRaisedEvent(amount));
}

68. Entidade/Agregado gera Eventos
public void ChangeHomeAddress(Address address)
{
Throw.IfArgumentIsNull(address, nameof(address));
Update(new EmployeeHomeAddressChangedEvent(address));
}

69. Atualiza estado a partir dos
Eventos
protected void Update(VersionedEvent<TId> e)
{
e.SourceId = Id;
e.Version = Version + 1;
_handlers[e.GetType()].Invoke(e);
Version = e.Version;
_pendingEvents.Add(e);
}

70. Atualiza estado a partir dos
Eventos
protected void Update(VersionedEvent<TId> e)
{
e.SourceId = Id;
e.Version = Version + 1;
_handlers[e.GetType()].Invoke(e);
Version = e.Version;
_pendingEvents.Add(e);
}
private Employee(Guid id) : base(id)
{
Handles<EmployeeRegisteredEvent>(OnEmployeeRegistered);
Handles<EmployeeSalaryRaisedEvent>(OnEmployeeSalaryRaised);
Handles<EmployeeHomeAddressChangedEvent>(OnEmployeeHomeAddressChanged);
}

71. Atualiza estado a partir dos
Eventos
protected void Update(VersionedEvent<TId> e)
{
e.SourceId = Id;
e.Version = Version + 1;
_handlers[e.GetType()].Invoke(e);
Version = e.Version;
_pendingEvents.Add(e);
}
private void OnEmployeeRegistered(EmployeeRegisteredEvent @event)
{
Name = @event.Name;
Salary = @event.InitialSalary;
}
private void OnEmployeeSalaryRaised(EmployeeSalaryRaisedEvent @event)
{
Salary += @event.Amount;
}

72. Atualiza estado a partir dos
Eventos
protected void Update(VersionedEvent<TId> e)
{
e.SourceId = Id;
e.Version = Version + 1;
_handlers[e.GetType()].Invoke(e);
Version = e.Version;
_pendingEvents.Add(e);
}

73. Stream de Eventos
EmployeeRegistered
HomeAddressUpdated
SalaryRaised
SalaryRaised
HomeAddressUpdated
SalaryRaised
Por que não salvar?

74. Application
(InputModel)
CommandHandler
(Command)
Entidade
(Evento)

75. Application
(InputModel)
CommandHandler
(Command)
Entidade
(Evento)

76. Application
(InputModel)
CommandHandler
(Command)
Entidade
(Evento)

77. Salvar um documento com
eventospublic void Save(Employee employee)
{
var head = GetHead(employee.Id);
var storedVersion = GetStoredVersionOf(head);
if (storedVersion != (employee.Version - employee.PendingEvents.Count()))
throw new InvalidOperationException("Invalid object state.");
if (head == null)
{
SaveNewEmployee(employee);
}
else
{
SaveEmployeeEvents(employee);
}
foreach (var evt in employee.PendingEvents)
Bus.RaiseEvent(evt);
}

78. Salvar um documento com
eventos
public JsonDocumentMetadata GetHead(Guid id)
{
string localId = $"employees/{id}";
return _store.DatabaseCommands.Head(localId);
}
public int GetStoredVersionOf(JsonDocumentMetadata
head)
{
return head
?.Metadata[EmployeeEntityVersion]
.Value<int>() ?? 0;
}

79. Salvar um documento com
eventospublic void Save(Employee employee)
{
var head = GetHead(employee.Id);
var storedVersion = GetStoredVersionOf(head);
if (storedVersion != (employee.Version - employee.PendingEvents.Count()))
throw new InvalidOperationException("Invalid object state.");
if (head == null)
{
SaveNewEmployee(employee);
}
else
{
SaveEmployeeEvents(employee);
}
foreach (var evt in employee.PendingEvents)
Bus.RaiseEvent(evt);
}

80. Salvar um documento com
eventos
private void SaveNewEmployee(Employee employee)
{
using (var session = _store.OpenSession())
{
var document = new EmployeeEvents(
employee.Id,
employee.PendingEvents
);
session.Store(document);
session.Advanced.GetMetadataFor(document)
.Add(EmployeeEntityVersion, employee.Version);
session.SaveChanges();
}
}

81. private void SaveEmployeeEvents(
Employee employee )
{
var patches = new List<PatchRequest>();
foreach (var evt in employee.PendingEvents)
{
patches.Add(new PatchRequest
{
Type = PatchCommandType.Add,
Name = "Events",
Value = RavenJObject.FromObject(evt, _serializer)
});
}
var localId = $"employees/{employee.Id}";
var addEmployeeEvents = new PatchCommandData()
{
Key = localId,
Patches = patches.ToArray()
};
var updateMetadata = new ScriptedPatchCommandData()
{
Key = localId,
Patch = new ScriptedPatchRequest
{
Script = $"this['@metadata']['{EmployeeEntityVersion}'] = {employee.Version}; "
}
};
_store.DatabaseCommands.Batch(new ICommandData[]
{
addEmployeeEvents,
updateMetadata
});
}

82. private void SaveEmployeeEvents(
Employee employee )
{
var patches = new List<PatchRequest>();
foreach (var evt in employee.PendingEvents)
{
patches.Add(new PatchRequest
{
Type = PatchCommandType.Add,
Name = "Events",
Value = RavenJObject.FromObject(evt, _serializer)
});
}
var localId = $"employees/{employee.Id}";
var addEmployeeEvents = new PatchCommandData()
{
Key = localId,
Patches = patches.ToArray()
};
var updateMetadata = new ScriptedPatchCommandData()
{
Key = localId,
Patch = new ScriptedPatchRequest
{
Script = $"this['@metadata']['{EmployeeEntityVersion}'] = {employee.Version}; "
}
};
_store.DatabaseCommands.Batch(new ICommandData[]
{
addEmployeeEvents,
updateMetadata
});
}

83. private void SaveEmployeeEvents(
Employee employee )
{
var patches = new List<PatchRequest>();
foreach (var evt in employee.PendingEvents)
{
patches.Add(new PatchRequest
{
Type = PatchCommandType.Add,
Name = "Events",
Value = RavenJObject.FromObject(evt, _serializer)
});
}
var localId = $"employees/{employee.Id}";
var addEmployeeEvents = new PatchCommandData()
{
Key = localId,
Patches = patches.ToArray()
};
var updateMetadata = new ScriptedPatchCommandData()
{
Key = localId,
Patch = new ScriptedPatchRequest
{
Script = $"this['@metadata']['{EmployeeEntityVersion}'] = {employee.Version}; "
}
};
_store.DatabaseCommands.Batch(new ICommandData[]
{
addEmployeeEvents,
updateMetadata
});
}

84. Salvar um documento com
eventospublic void Save(Employee employee)
{
var head = GetHead(employee.Id);
var storedVersion = GetStoredVersionOf(head);
if (storedVersion != (employee.Version - employee.PendingEvents.Count()))
throw new InvalidOperationException("Invalid object state.");
if (head == null)
{
SaveNewEmployee(employee);
}
else
{
SaveEmployeeEvents(employee);
}
foreach (var evt in employee.PendingEvents)
Bus.RaiseEvent(evt);
}

85. Carregar um documento com
eventos
public Employee Load(Guid id)
{
EmployeeEvents data;
using (var session = _store.OpenSession())
{
data = session.Load<EmployeeEvents>(id);
}
return new Employee(id, data.Events);
}
public Employee(Guid id,
IEnumerable<IVersionedEvent<Guid>> history)
: this(id)
{
LoadFrom(history);
}

86. Carregar um documento com
eventos
protected void LoadFrom(IEnumerable<IVersionedEvent<TId>> pastEvents)
{
foreach (var e in pastEvents)
{
_handlers[e.GetType()].Invoke(e);
Version = e.Version;
}
}

88. elemarjr.com
@elemarjr
linkedin.com/in/elemarjr
elemarjr@ravendb.net
elemarjr@gmail.com
Mantenha contato!

89. CQRS e Event Sourcing na
prática com RavenDB
Elemar Júnior
@elemarjr
elemarjr@ravendb.net
elemarjr@gmail.com
elemarjr.com