Spring data - webflux - Chaining requests - spring-webflux

Question

i use reactive Mongo Drivers and Web Flux dependancies
I have a code like below.
public Mono<Employee> editEmployee(EmployeeEditRequest employeeEditRequest) {
return employeeRepository.findById(employeeEditRequest.getId())
.map(employee -> {
BeanUtils.copyProperties(employeeEditRequest, employee);
return employeeRepository.save(employee)
})
}
Employee Repository has the following code
Mono<Employee> findById(String employeeId)
Does the thread actually block when findById is called? I understand the portion within map actually blocks the thread.
if it blocks, how can I make this code completely reactive?
Also, in this reactive paradigm of writing code, how do I handle that given employee is not found?

Answer 1

Yes, map is a blocking and synchronous operation for which time taken is always going to be deterministic.
Map should be used when you want to do the transformation of an object /data in fixed time. The operations which are done synchronously. eg your BeanUtils copy properties operation.
FlatMap should be used for non-blocking operations, or in short anything which returns back Mono,Flux.
"how do I handle that given employee is not found?" -
findById returns empty mono when not found. So we can use switchIfEmpty here.
Now let's come to what changes you can make to your code:
public Mono<Employee> editEmployee(EmployeeEditRequest employeeEditRequest) {
return employeeRepository.findById(employeeEditRequest.getId())
.switchIfEmpty(Mono.defer(() -> {
//do something
}))
.map(employee -> {
BeanUtils.copyProperties(employeeEditRequest, employee);
return employee;
})
.flatMap(employee -> employeeRepository.save(employee));
}