spring boot webflux query data in continuous flux-CodePudding

having the following code that produces a continuous flux of random strings :

@RestController
public class WebFluxController {

private final Random random = new Random();
                  
@CrossOrigin         
@GetMapping(value = "/documents")         
public Flux getDocuments() {                          
        return Flux.interval(Duration.ofSeconds(1))     .map(x -> "document-"   
 random.nextDouble());         
    }
}

...how can I replace the random with a query to the database that will return a field of the last record, something like :

@RestController
public class WebFluxController {

@Autowired
private ReactiveDocumentRepository reactiveDocumentRepository;

@CrossOrigin     @GetMapping(value = "/documents")     
public Flux getDocuments() {                  
    return Flux.interval(Duration.ofSeconds(1))     .map(x -> "document-"   
 reactiveDocumentRepository.findLastDocument().map(d->d.getDescription);     
        }
    }
}

...where reactiveDocumentRepository.findLastDocument() returns a mono containing last document inserted in the db? In other words, I want that query to be ran continuously over the database and publish last inserted record all the time

CodePudding user response：

In reactive you need to build a flow using operators that will be evaluated when downstream (in your case webflux) subscribes to the flow. Result is not immediately available and you can't just concatenate it with a string. reactiveDocumentRepository.findLastDocument() is reactive and you need to use flatMap instead of map.

public Flux getDocuments() {        
    return Flux.interval(Duration.ofSeconds(1))    
            .flatMap(x -> 
                    reactiveDocumentRepository.findLastDocument()
                            .map(d -> "document-"   d.getDescription)
            );
}