org.elder.sourcerer.OperationHandler Maven / Gradle / Ivy
package org.elder.sourcerer;
import java.util.List;
/**
* Functional interfaces for handler functions providing the logic for Operations.
* org.elder.sourcerer.functions contain specializations of this interface matching a number of
* handler signatures for various types of operations. {@link Operation} type.
*
* @param The type of aggregates that this operation acts on.
* @param The type of parameters that this operation accepts.
* @param The type of event that this operation produces.
*/
public interface OperationHandler {
/**
* Execute the operation. An operation should return a list of events to be appended to an
* aggregate if the command it represents is valid in the current state of the aggregate and
* given the provided parameters.
*
* An operation may make use of other state and external resources in order to determine whether
* it is valid in the current state, and if so what the resulting events should be (so does not
* have to be a pure function). However, an operation should not attempt to modify any state
* related to the aggregate it operates on other than in the form of returning events, and does
* need to be written to support retries.
*
* @param state The aggregate that the operation is executed on.
* @param params The arguments applied to the operation.
* @return A list of events to be applied to the aggregate to update its state, may be empty if
* the operation is a no-op, must not be null,
*/
List execute(TState state, TParams params);
}