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Details in CQRS pattern - Azure Architecture Center | Microsoft Learn |
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.
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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
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CREATE MATERIALIZED VIEW customer_order_totals AS
SELECT customer_id, SUM(order_amount) AS total_amount
FROM orders
GROUP BY customer_id; |
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SELECT * FROM my_materialized_view; |