如何获取@RepositoryRestResource生成的嵌套REST数据及优化Traverson调用

Hey there! Since you're new to HAL and HATEOAS, let's walk through your two requirements with clear, actionable steps:

1. Get Category (or its link) in a single Traverson request without adding new @JsonProperty annotations #

Spring Data REST automatically handles associations by either exposing them as links (in the _links section) or allowing you to embed them using the expand parameter—no need to add extra @JsonProperty to your entities. Here are two approaches:

Option A: Fetch the Category link #

Spring Data REST adds a category link under each Joke's _links by default. To capture this in your JokesDTO, just add a field to map the link URL:

@Builder(toBuilder = true)
@Value
@JsonDeserialize(builder = JokesDTO.JokesDTOBuilder.class)
@JsonInclude(Include.NON_NULL)
public class JokesDTO {
    private String content;
    // Map the category link from HAL's _links section
    @JsonProperty("_links.category.href")
    private String categoryLink;

    @JsonPOJOBuilder(withPrefix = "")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class JokesDTOBuilder {
    }
}

Your existing Traverson code works as-is—no changes needed. The categoryLink will now hold the URL to fetch the full Category details later if you need it.

Option B: Embed full Category data in one request #

Use Spring Data REST's expand query parameter to embed the Category directly in the Joke response. First, create a CategoryDTO to map the Category data:

@Builder(toBuilder = true)
@Value
@JsonDeserialize(builder = CategoryDTO.CategoryDTOBuilder.class)
@JsonInclude(Include.NON_NULL)
public class CategoryDTO {
    private int id;
    private String name;

    @JsonPOJOBuilder(withPrefix = "")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class CategoryDTOBuilder {
    }
}

Update your JokesDTO to include the embedded Category:

@Builder(toBuilder = true)
@Value
@JsonDeserialize(builder = JokesDTO.JokesDTOBuilder.class)
@JsonInclude(Include.NON_NULL)
public class JokesDTO {
    private String content;
    // Map the embedded Category from HAL's _embedded section
    @JsonProperty("_embedded.category")
    private CategoryDTO category;

    @JsonPOJOBuilder(withPrefix = "")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class JokesDTOBuilder {
    }
}

Modify your Traverson call to include the expand parameter:

Traverson client = new Traverson(URI.create("http://localhost:8080/api/"), MediaTypes.HAL_JSON);
HashMap<String, Object> parameters = Maps.newHashMap();
parameters.put("size", "2");
parameters.put("expand", "category"); // Add this to embed Category
PagedModel<JokesDTO> jokes = client
        .follow("jokes")
        .withTemplateParameters(parameters)
        .toObject(new PagedModelType<JokesDTO>() {
        });
return jokes;

This will return the full Category data alongside each Joke in one request.

2. Expose a custom query via @RepositoryRestResource to fetch all associated data in one go #

You can use Spring Data REST's repository query methods with fetch joins or projections to grab Jokes and their Categories in a single database call. Here are two easy ways:

Option A: Custom repository query with fetch join #

Create a custom query in your JokeRepository using JOIN FETCH to load Categories alongside Jokes:

@RepositoryRestResource(collectionResourceRel = "jokes", path = "jokes")
public interface JokeRepository extends JpaRepository<Joke, Long> {
    // Fetch Jokes and their associated Categories in one query
    @Query("SELECT j FROM Joke j JOIN FETCH j.category")
    Page<Joke> findAllWithCategory(Pageable pageable);
}

Spring Data REST automatically exposes this as a search endpoint at /api/jokes/search/findAllWithCategory. Update your Traverson call to follow this search link:

Traverson client = new Traverson(URI.create("http://localhost:8080/api/"), MediaTypes.HAL_JSON);
HashMap<String, Object> parameters = Maps.newHashMap();
parameters.put("size", "2");
PagedModel<JokesDTO> jokes = client
        .follow("jokes", "search", "findAllWithCategory") // Navigate to the custom query
        .withTemplateParameters(parameters)
        .toObject(new PagedModelType<JokesDTO>() {
        });

Update your JokesDTO to include the CategoryDTO field directly (no _embedded prefix needed here, since the fetch join loads the data upfront):

@Builder(toBuilder = true)
@Value
@JsonDeserialize(builder = JokesDTO.JokesDTOBuilder.class)
@JsonInclude(Include.NON_NULL)
public class JokesDTO {
    private String content;
    private CategoryDTO category;

    @JsonPOJOBuilder(withPrefix = "")
    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class JokesDTOBuilder {
    }
}

Option B: Use a Spring Data REST Projection #

Projections are a simpler way to shape the response without writing custom queries. Create a projection interface for Jokes that includes the Category:

@Projection(name = "withCategory", types = Joke.class)
public interface JokeWithCategoryProjection {
    String getContent();
    Category getCategory(); // Expose the full Category entity
}

Then, use the projection parameter in your Traverson call to activate this projection:

Traverson client = new Traverson(URI.create("http://localhost:8080/api/"), MediaTypes.HAL_JSON);
HashMap<String, Object> parameters = Maps.newHashMap();
parameters.put("size", "2");
parameters.put("projection", "withCategory"); // Use the projection
PagedModel<JokesDTO> jokes = client
        .follow("jokes")
        .withTemplateParameters(parameters)
        .toObject(new PagedModelType<JokesDTO>() {
        });

This will return Jokes with their full Category data in one request, and you don't need to modify your repository interface beyond the default setup.

内容的提问来源于stack exchange，提问作者kingkong