Created
March 3, 2012 03:19
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CQS_and_CQRS
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| // CQS (Command-Query Separation) | |
| // Bertrand Meyer devised the CQS principle | |
| // It states that every method should either be a command that performs an action, or a | |
| // query that returns data to the caller, but not both. In other words, asking a question | |
| // should not change the answer. More formally, methods should return a value only if they | |
| // are referentially transparent and hence possess no side effects. | |
| // | |
| // Example: | |
| public class CustomerService | |
| { | |
| // Commands | |
| void MakeCustomerPreferred(CustomerId) | |
| void ChangeCustomerLocale(CustomerId, NewLocale) | |
| void CreateCustomer(Customer) | |
| void EditCustomerDetails(CustomerDetails) | |
| // Queries | |
| Customer GetCustomer(CustomerId) | |
| CustomerSet GetCustomersWithName(Name) | |
| CustomerSet GetPreferredCustomers() | |
| } | |
| // CQRS (Command-Query Responsibility Segregation) | |
| // Defined by Greg Young. | |
| // CQRS is simply the creation of two objects where there was previously only one | |
| // http://codebetter.com/gregyoung/2010/02/16/cqrs-task-based-uis-event-sourcing-agh/ | |
| // | |
| // Example: | |
| public class CustomerWriteService | |
| { | |
| // Commands | |
| void MakeCustomerPreferred(CustomerId) | |
| void ChangeCustomerLocale(CustomerId, NewLocale) | |
| void CreateCustomer(Customer) | |
| void EditCustomerDetails(CustomerDetails) | |
| } | |
| public class CustomerReadService | |
| { | |
| // Queries | |
| Customer GetCustomer(CustomerId) | |
| CustomerSet GetCustomersWithName(Name) | |
| CustomerSet GetPreferredCustomers() | |
| } |
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Interfaces, surely! (Couldn't resist.)