CQRS is a pattern for handling data: the Command Query Responsibility Separation. see: Wikipedia

• Command: unit of work which writes to one or more data sources (may also read from one or more data sources)
• Query: unit of work which reads from one or more data sources (should not write to any, except logging, if necessary)
• Executor: logical construct which executes one or more commands and or queries

1. Define commands and / or queries by defining new classes which derive from Command<T> or Query<T>
2. You must override the Execute method in your derived class. The logic within there must, if possible, set the Result property on the command or query it belongs to
3. You may override the Validate method in your derived class. Command/Query executors will run this logic before attempting to Execute. Any exception thrown within the Validate method will prevent command / query execution.
4. Execute commands with an instance of CommandExecutor. Execute queries with an instance of QueryExecutor
5. You must configure the behavior of Codeo.CQRS with Fluently.Configure()
   1. You must at least specify a connection factory with WithConnectionProvider
   2. You may register Sql mappings via the WithEntitiesFrom method, though this is optional: unknown entity types will be registered on fist use
   3. You may register exception handlers via the WithExceptionHandler method
      1. if your exception handler is invoked and does not throw, the default value for the queried type is returned
      2. if your exception handler throws, that exception bubbles up
      3. if there is no exception handler for the type of exception which is caught by an executor, it bubbles up

See TestQueryExecution.cs for examples