CQRS, Event Sourcing and Microservices

Marcelo Cure

CQRSCommand Query Responsibility Segregation

Pattern;

Greg Young;

Separation of Reads and Writes in Commands and Queries;

Commands - mutates state;

Queries - returns a value;

Draw it for me

Pros/ConsPros

Separate write/read logic;

Use separated databases for read/write;

Helps system with complex domain;

Cons

Generates complexity;

When to use or not ...Use

Complex domain;

DDD;

Specific bounded-contexts;

Do not use

In the whole system;

Too simple systems;

CustomerService exampleCustomer GetCustomer(CustomerId);

CustomerSet GetCustomersWithName(Name);

CustomerSet GetPreferredCustomers();

void MakeCustomerPreferred(CustomerId);

void ChangeCustomerLocale(CustomerId, NewLocale);

void CreateCustomer(Customer);

void EditCustomerDetails(CustomerDetails);

Applying CQRSCustomerWriteService

void MakeCustomerPreferred(CustomerId)

void ChangeCustomerLocale(CustomerId, NewLocale)

void CreateCustomer(Customer)

void EditCustomerDetails(CustomerDetails)

CustomerReadService

Customer GetCustomer(CustomerId)

CustomerSet GetCustomersWithName(Name)

CustomerSet GetPreferredCustomers()

Each application state change is a new event;

Sequence of events;

Reconstruct past states with event log (replay);

Events can generate other events;

Event Sourcing

Draw it for me

For each action:

Store event in Event Store;

Aggregate;

Propagate event;

Example - order creation

Alltogethernow

Thanks