Trait cqrs_es::Command

pub trait Command<A, E> where
    A: Aggregate,
    E: DomainEvent<A>, {
    fn handle(self, aggregate: &A) -> Result<Vec<E>, AggregateError>;
}

A Command represents a request to modify the state of an Aggregate by producing DomainEvents.

A Command is always named in the imperative, e.g.,

• GrantAdminPrivileges
• ChangeEmailAddress
• AddDependency

In it's simplest form a Command is a simple data object (possibly with no data if it represents a boolean change to the system), but usually they are implemented with the derived Serialize and Deserialize traits for use in a Restful endpoint.

Examples

pub struct ChangeName {
    pub changed_name: String
}

Required methods

fn handle(self, aggregate: &A) -> Result<Vec<E>, AggregateError>

The user should implement all business logic within the handle method of a Command. As input the current state of the aggregate is provided, from which a list of DomainEvents is returned if the command is accepted.

If the command is rejected an AggregateError (AggregateError::UserError in nearly all instances) should carry a message for the user as to why the request was rejected.

Error

If any business rules were violated an AggregateError should be returned to warn the user.

Examples

impl Command<Customer, CustomerEvent> for AddCustomerName {
    fn handle(self, customer: &Customer) -> Result<Vec<CustomerEvent>, AggregateError> {
        if customer.name.as_str() != "" {
            return Err(AggregateError::new("a name has already been added for this customer"));
        }
        let payload = NameAdded {
            changed_name: self.changed_name
        };
        Ok(vec![CustomerEvent::NameAdded(payload)])
    }
}

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Implementors

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