Seonglae ChoCommand Query Separation
- Don't return the object created or updated
- Do query separately
Important Principle of Imperative Programming
Conceived in Bertrand Meyer's Eiffel programming language
Every method should perform only one action: either a command that changes state or a query that returns data
Don't modify the answer when performing an action on a request
In other words, state modification and data return should be implemented separately - this is the theoretical foundation of get and set
Methods should be referentially transparent when returning values (a function is referentially transparent when it doesn't change the system's state) and should not cause side effects
While widely used, the most common problem arising from this is Race Condition
- Query - Returns a result value and does not change the observable state of the system. Therefore, it is free of side effects.
- Command - Does not return a result, but instead changes the state of the system.
