Mapstruct - Ambiguous mapping methods found for mapping property

Question

I am using mapstruct to map from one DTO to another. I have multiple default methods , but 2 of them with a return value of String and that uses the same class as the input parameter gives me "Ambiguous mapping methods using java Mapstruct" error. I am adding the relevant parts of the code here:

@Mappings({
     @Mapping(source = "programInstance", target = "title", qualifiedByName = "title"),
     @Mapping(source = "programInstance", target = "seriesName", qualifiedByName = "seriesName"),
     @Mapping(source = "programInstance", target = "season", qualifiedByName = "season"),
     @Mapping(source = "programInstance", target = "epNumber", qualifiedByName = "epNumber"),
 })
 DTO1 mapDTOs (DTO2 dto2);

  @Named("title")
default String mapTitle(Program programInstance) {
    Optional<String> title = Utils.getObject(() -> programInstance.getTitle().getDescriptions().get(0).getValue());
    if (title.isPresent())
        return title.get();
    return null;
}
@Named("seriesName")
default String mapSeriesName(Program programInstance) {
    Optional<String> seriesName = Utils.getObject(() -> programInstance.get(0).getProgram().getTitle().getDescriptions().get(0).getValue());
    if (seriesName.isPresent())
        return seriesName.get();
    return null;
}
 @Named("season")
default Integer mapSeasonNumber(Program programInstance) {
    Optional<Integer> season = Utils.getObject(() -> programInstance.get(0).getSeasonOf().get(0).getOrderNo());
    if (season.isPresent())
        return season.get();
    return null;
}

@Named("epNumber")
default Integer mapEpNumber(Program programInstance) {
    Optional<Integer> epNumber = Utils.getObject(() -> programInstance.getEpOf().get(0).getOrderNo());
    if (epNumber.isPresent())
        return epNumber.get();
    return null;
}

The error is

Ambiguous mapping methods found for mapping property "Program programInstance" to java.lang.String: java.lang.String mapTitle(), java.lang.String mapSeriesName().

Are you sure that you are using `org.mapstruct.Named` and not some other one? — Filip, Feb 11 '19 at 06:31
but.. I also spotted the name of the method deviates.. `mapSeriesName`.. Your example has a signature `mapSeriesName1 `.. Do you by any chance point to a used mapper? Are there more methods that carry the same `@Named`? — Sjaak, Feb 11 '19 at 18:43
sjaak: that was a type, sorry, edited the code. My version was 1.2, tried changing to 1.3 now - the error still exists.. Yes, I have more @Named methods that carry the same source Program.. — ljs, Feb 11 '19 at 19:16
edited code to add the other methods that use Program as the source — ljs, Feb 11 '19 at 19:24
just out of curiosity, if you add ignore=true to the 2 String mappings.. does MapStruct complain about the Integer mappings as well? — Sjaak, Feb 11 '19 at 21:49
Is there anyway (e.g. gist) that you can share the DTO's as well. I can give it a shot tomorrow.. — Sjaak, Feb 11 '19 at 21:51
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/188239/discussion-between-ljs-and-sjaak). — ljs, Feb 11 '19 at 23:40

score 8 · Accepted Answer · edited Aug 27 '19 at 22:52

I checked your example.. The problem is that the fields you try to target are of type String.

So:

public class IvpVodOfferStatusDTO {

    private String seasonNumber;
    private String episodeNumber;
}

MapStruct tries to match this with the signature you provide:

 @Named("season")
default Integer mapSeasonNumber(Program programInstance) {
    Optional<Integer> season = Utils.getObject(() -> programInstance.get(0).getSeasonOf().get(0).getOrderNo());
    if (season.isPresent())
        return season.get();
    return null;
}

@Named("epNumber")
default Integer mapEpNumber(Program programInstance) {
    Optional<Integer> epNumber = Utils.getObject(() -> programInstance.getEpOf().get(0).getOrderNo());
    if (epNumber.isPresent())
        return epNumber.get();
    return null;
}

MapStruct has a predefined order of attempts:

User provided Mapping method
Direct (types source -target are the same)
Mapping method (built-in)
Type conversion

If this all fails MapStruct tries to do a number of 2 step approaches:

mapping method - mapping method
mapping method - type conversion
type conversion - mapping method

At 6. it finds 2 qualifying methods (Program to String). It's probably an error in MapStruct that it selects methods that do not qualify (need to check whether this is intentional) by the @Named. Otherwise, I'll write an issue.

The most easy solution is: adapt the target:

public class IvpVodOfferStatusDTO {

    private Integer seasonNumber;
    private Integer episodeNumber;
}

What is probably what you intend (I guess).. Otherwise you could change the signature not to return an Integer but a String

sabeena kumarawadu · Answer 2 · 2022-07-04T07:42:31.063

Even if the data types are matching, this could happen if the name given at qualifiedByName is not defined in as a bean instance

Because without a matching @Named qualifier, the injector would not know which bean to bind to which variable

@Mapping( source = "firstName", target = "passenger.firstName", qualifiedByName = "mapFirstName" )
public abstract Passenger mapPassenger( Traveller traveller );

@Named( "mapFirstName" )
String mapFirstName( String firstName)
{
}

score 2 · Answer 3 · answered Mar 11 '21 at 18:34

I was facing same issue and observed that, there was same method inherited by my mapper class using @Mapper(uses = {BaseMapper.class}) and using extends BaseMapper. Removing extends solved the problem for me. So, you can look for method received by custom mapper through multiple ways.

score 0 · Answer 4 · answered May 30 '23 at 13:01

0

Also note you may get this if you have cyclic dependency:

ObjectA -> ObjectB -> ObjectA -> ObjectB

It will be reported as an ambiguous entry most of the time. The solution is to not refer to Object A in ObjectB.

answered May 30 '23 at 13:01

PeterS

2,818
23
36

score 0 · Answer 5 · answered Aug 31 '23 at 19:55

0

Ambiguous mapping methods can also happen if a @Named("name") method annotation is duplicated with the same "name": They need to be unique across @Named methods.

answered Aug 31 '23 at 19:55

cellepo

4,001
2
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Mapstruct - Ambiguous mapping methods found for mapping property

5 Answers5