Spring Data Rest Ambiguous Association Exception

问题

The newly added LinkCollectingAssociationHandler is throwing a MappingException due to an ambiguous association in my domain class.

The links array looks like this:

[<http://localhost:8080/rooms/2/roomGroups>;rel="roomGroups", <http://localhost:8080/rooms/2/userGroup>;rel="userGroup", <http://localhost:8080/rooms/2/room>;rel="room", <http://localhost:8080/rooms/2/originatingConferences>;rel="originatingConferences", <http://localhost:8080/rooms/2/user>;rel="user"]

And it is trying to add another 'room' relation when it throws the exception.

The issue is that it seems to be adding links to relations which I have explicitly marked with @RestResource(exported = false)

Here is an example of a relation which I believe is causing this issue:

@JsonIgnore
@RestResource(exported = false)
@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.room", cascade = {CascadeType.REMOVE})
private Set<RoomsByUserAccessView> usersThatCanDisplay = new HashSet<>(); 

The type RoomsByUserAccessView has an embedded id made up of a Room and a User.

I have also annotated the embedded id property with:

@JsonIgnore
@RestResource(exported = false)
private RoomsByUserAccessViewId pk = new RoomsByUserAccessViewId();

and its properties like this:

@JsonIgnore
@RestResource(exported = false)
private Room room;

@JsonIgnore
@RestResource(exported = false)
private User userWithAccess;

public RoomsByUserAccessViewId() {
    //
}

How can I get it to ignore these relations properly when serializing to JSON?

My code was working prior to DATAREST-262 (https://github.com/spring-projects/spring-data-rest/commit/1d53e84cae3d09b09c4b5a9a4caf438701527550)

The full error message returned when I try to visit the rooms/ endpoint is as follows:

{ timestamp: "2014-03-17T13:38:05.481-0500" error: "Internal Server Error" status: 500 exception: "org.springframework.http.converter.HttpMessageNotWritableException" message: "Could not write JSON: Detected multiple association links with same relation type! Disambiguate association @com.fasterxml.jackson.annotation.JsonIgnore(value=true) @javax.persistence.ManyToOne(fetch=EAGER, cascade=[], optional=true, targetEntity=void) @org.springframework.data.rest.core.annotation.RestResource(description=@org.springframework.data.rest.core.annotation.Description(value=), path=, exported=false, rel=) private com.renovo.schedulerapi.domain.Room com.renovo.schedulerapi.domain.RoomsByUserAccessViewId.room using @RestResource! (through reference chain: org.springframework.hateoas.PagedResources["content"]->java.util.UnmodifiableCollection[0]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Detected multiple association links with same relation type! Disambiguate association @com.fasterxml.jackson.annotation.JsonIgnore(value=true) @javax.persistence.ManyToOne(fetch=EAGER, cascade=[], optional=true, targetEntity=void) @org.springframework.data.rest.core.annotation.RestResource(description=@org.springframework.data.rest.core.annotation.Description(value=), path=, exported=false, rel=) private com.renovo.schedulerapi.domain.Room com.renovo.schedulerapi.domain.RoomsByUserAccessViewId.room using @RestResource! (through reference chain: org.springframework.hateoas.PagedResources["content"]->java.util.UnmodifiableCollection[0])" }

回答1:

I had a very similar problem . When adding a bidirectional relationship between two entities

I got an exception ""Could not write JSON: Detected multiple association links with same

relation type!" , While trying some solutions that i found here

(@JsonIgnore, @JsonIdentity, @RestResource, I also tried to do what Oliver offered )

(The relation was properly defined with @JsonManagedReference and @JsonBackReference)

Nothing helped.

At the end i managed to understand that spring data rest is trying to

figure out if the related entity is linkable ( while trying to build the json of the

requested entity )

(LinkCollectingAssociationHandler : doWithAssociation -> isLinkableAssociation)

, For doing that he is looking for a repository that deals with the

related entity. After adding a repository for the related entity.. works like a charm..

(I suppose that after adding a repo a mapping RepositoryAwareResourceInformation is being

created for this entity (that is what I saw at debug).

回答2:

I had this issue, and solved it as Ron suggests, but I thought I would expound a little. I didn't fully understand the first couple times I read Ron's answer...

@NodeEntity
public class Player extends Entity

@NodeEntity
public class PlayerTrade extends Entity

@NodeEntity
public class Trade extends Entity

I had repositories for Player and Trade, but none for PlayerTrade:

@RepositoryRestResource
public interface PlayerRepository  extends GraphRepository<Player> {

@RepositoryRestResource
public interface TradeRepository extends GraphRepository<Trade> {

As soon as I added the last repo it worked.

@RepositoryRestResource
public interface PlayerTradeRepository extends GraphRepository<PlayerTrade> 

I tried using @RestResource with rel or excluded, but couldn't get it dialed in. Does this mean that every entity in our JSON graph must have a repository?

来源：https://stackoverflow.com/questions/22462826/spring-data-rest-ambiguous-association-exception