Command and Query Responsibility Segregation

Breaking the CRUD

CRUD works for limited business logic operations

CRUD can

• lead to potentially unnecessary updates for certain operations
• affect performance : prevents concurrent updates and implies load of excessive data
• bring security and permission management overhead

CQRS => Separation of concern

Two separate data models:

Query Models read data from store

Command Models write data to store

Allows scaling of read ad write independently

CQRS => risky complexity

Use only in bounded context (limited sections of the system)

Dealing with resiliency and eventual consistency with event sourcing :

• the store of event as a write model
• materialised views as the read-only cache of data 

Related Patterns :

• Data Consistency Primer
• Data Partitioning Guidance
• Event Sourcing Pattern
• Materialized View Pattern