Problem Parsing request body of type json, containing a list of string to Flux of string in Spring reactive

Question

I have a DTO as below:

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import reactor.core.publisher.Flux;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class InternetPackageDto {
    private String id;

    private String name;

    private String termsAndConditions;

    private String price;

    private Flux<String> packageAttributes;

    private Flux<String> extras;
}

And a Database Object as below:

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;
import reactor.core.publisher.Flux;

@Document("internet_packages")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class InternetPackage {
    @Id
    private String id;

    private String name;

    private String termsAndConditions;

    private String price;

    private Flux<StoreableAttribute> attributes;

    private Flux<StoreableAttribute> extras;
}

The StorableAttribute Database Model like so:

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document("package_attributes")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class StoreableAttribute {
    @Id
    private String id;

    private String name;

    private String description;
}

On the Data Object the fields: Flux<StoreableAttribute> attributes and Flux<StoreableAttribute> extras are stored in a separate collection alongside the Package Object. And is handled by the mapper as below:

 public InternetPackage fromDto(InternetPackageDto dto) {
        var internetPackage = new InternetPackage();

        internetPackage.setName(dto.getName());
        internetPackage.setPrice(dto.getPrice());
        internetPackage.setId(dto.getId());
        internetPackage.setExtras(this.resolePackageExtras(dto));
        internetPackage.setAttributes(this.resolePackageAttributes(dto));

        return internetPackage;
    }

  private Flux<StoreableAttribute> resolePackageExtras(InternetPackageDto dto) {
        return this.storeableAttributeService.resolveAttributes(dto.getExtras());
    }

for the extra and similarly for the attributes also.

And a simple controller method as below:

    @PostMapping(produces = MediaType.APPLICATION_JSON_VALUE, consumes =  MediaType.APPLICATION_JSON_VALUE)
    public Mono<InternetPackageDto> update(@RequestBody InternetPackageDto incomingPackageDto) {
        return this.packageService
                .updatePackage(this.dtoMapper.fromDto(incomingPackageDto))
                .map(this.dtoMapper::toDto);
    }

And when I make a post request I get an error stating

org.springframework.core.codec.CodecException: Type definition error: [simple type, class reactor.core.publisher.Flux]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `reactor.core.publisher.Flux` (no Creators, like default constructor, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (io.netty.buffer.ByteBufInputStream); line: 2, column: 13] (through reference chain: com.example.api.dto.InternetPackageDto["extras"])

Some more information:

1. I am using the class InternetPackageDto as a request object as well as a response object.
2. I am using Flux<String> and not List<String> since I wasn't sure if doing blocking resolution to list was a good idea.
3. The attributes are stored and managed separately.
4. And during the time of updating or inserting the package those; if a new extra or attribute is included the attributes collection in db will be updated with the insertion of new incoming extras and attributes.

It seems like I might have made a stupid mistake because I cannot find much information about this problem, or I am doing it completely wrong.

Any help would be greatly appreciated.

Answer 1

I think you should do smth like this

public Mono<InternetPackageDto> toDto(InternetPackage entity) {
    var internetPackage = new InternetPackageDto();

    internetPackage.setName(entity.getName());
    internetPackage.setPrice(entity.getPrice());
    internetPackage.setId(entity.getId());


    return Mono.zip(Mono.just(internetPackage), entity.getExtras().collectList(), entity.getAttributes().collectList())
            .flatMap(tu->{
                var dto = tu.getT1();
                dto.setExtras(tu.getT2()); //To make it work in my local i made entity.getAttributes() as Flux<String> so here you will probably need to use .stream().map(dbItem->dbItem.getPropertyName())
                dto.setPackageAttributes(tu.getT2());
                return Mono.just(dto);
            });
}