CQRS Pattern
- thierry sinassamy
Problem
In complex applications, read side and write side can become complicated. Read side can returns data transfer objects (DTOs) with different shapes; Write side can implement compex validation and business logic.
Solution
Separate the read from the write side :
example 1 : implement materialized view for the read side and stored procedures for the write side.
exemple 2 : implement 2 different data stores, one for the read side which is a document DB and the other, for the write side which is a relational DB.
…
public class ProductsCommandHandler :
ICommandHandler<AddNewProduct>, ICommandHandler<RateProduct>, ICommandHandler<AddToInventory>, ICommandHandler<ConfirmItemShipped>,
ICommandHandler<UpdateStockFromInventoryRecount>
{
private readonly IRepository<Product> repository;
public ProductsCommandHandler (IRepository<Product> repository)
{
this.repository = repository;
}
void Handle (AddNewProduct command)
{
...
}
void Handle (RateProduct command)
{
var product = repository.Find(command.ProductId);
if (product != null)
{
product.RateProduct(command.UserId, command.Rating);
repository.Save(product);
}
}
void Handle (AddToInventory command)
{
...
}
void Handle (ConfirmItemsShipped command)
{
...
}
void Handle (UpdateStockFromInventoryRecount command)
{
...
}
}CQRS In Practice : Materialized Views
A materialized view is a physical copy of the table that stores retrieved data from multiple tables in memory, which may result in higher query performance. A materialized view operates like a special notebook where the answers to questions you might ask the database are already written down.
CREATE MATERIALIZED VIEW customer_order_totals AS
SELECT customer_id, SUM(order_amount) AS total_amount
FROM orders
GROUP BY customer_id;SELECT * FROM my_materialized_view;