io.simplesource.api

Interface CommandHandler<K,C,E,A>

Type Parameters:

K - the aggregate key

C - all commands for this aggregate

E - all events generated for this aggregate

A - the aggregate

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface CommandHandler<K,C,E,A>

A command handler is responsible for accepting or rejecting commands and turning accepted commands into a list of events by applying the appropriate business logic and validations based on the current state. To assist in determining if a command is valid, the command handler has an internal aggregator that parses events as they are generated. The internal aggregator is guaranteed to be fully up-to-date at the point a new command is interpreted with the latest aggregate provided as an argument ready to use for validation and business logic.

Method Summary

Modifier and Type	Method and Description
static <K,C,E,A> CommandHandler<K,C,E,A>	ifSeq(CommandHandler<K,C,E,A> commandHandler) This method will wrap a CommandHandler in a check to ensure that the current aggregate sequence matches the expected aggregate sequence.
Result<CommandAPI.CommandError,NonEmptyList<E>>	interpretCommand(K key, Sequence expectedSeq, Sequence currentSeq, A currentAggregate, C command) Determine if you will accept or reject the given command given the current aggregate aggregate and transform into events.

Method Detail

interpretCommand

Result<CommandAPI.CommandError,NonEmptyList<E>> interpretCommand(K key,
                                                                 Sequence expectedSeq,
                                                                 Sequence currentSeq,
                                                                 A currentAggregate,
                                                                 C command)

Determine if you will accept or reject the given command given the current aggregate aggregate and transform into events.

Parameters:

key - the aggregate key the command applies to

expectedSeq - the sequence we expect the current aggregate to be at

currentSeq - the actual seq number of the current aggregate

currentAggregate - the aggregate for this aggregate guaranteed to be up to date with all events seen to date

command - the command to validate and convert into events

Returns:

If rejecting, return a failed Result providing one or more Reasons for the rejection. If accepting return one or more events that represent the command.

ifSeq

static <K,C,E,A> CommandHandler<K,C,E,A> ifSeq(CommandHandler<K,C,E,A> commandHandler)

This method will wrap a CommandHandler in a check to ensure that the current aggregate sequence matches the expected aggregate sequence. This is effectively an optimistic lock on the Aggregate.

Type Parameters:

K - the aggregate key

C - all commands for this aggregate

E - all events generated for this aggregate

A - the aggregate

Parameters:

commandHandler - the command handler that will be invoked if the sequence numbers match

Returns:

If rejecting, return a failed Result providing one or more Reasons for the rejection. If accepting return one or more events that represent the command.