Read/Write Model
Checkout lesson on UDEMY Section previewTerminology
CQS
Command Query Separation
Operation
A message that tells application | system to do something
- An operation is either a command or a query
Command
Change the state of aggregate
- Writes to the database
- An action initiated by an actor/user/service/time
- The ACTION must be carried out
- Named as verb
Query
Serves state of the aggregate
- Reads from the database
- Also known as Query Model or Read Model
Common model for Commands & Queries
Requires translation between Domain model and Read/Write models
CQS principle
Suggests clear demarcation between methods that change the state & those that don’t change the state of domain
Same object method should NOT be used for both command and query
Command and Query needs to deal with different set of concerns
In this illustration:
- Read model - looks for flexibility & performance
- Write model - deals with complex logic, need to be transactional & must scale
Command-Query Realization
- Synchronous & Asynchronous protocols
- Wire format is flexible