java - Neo4J:无法从具有多个元素的 Iterable 中提取单个值

Question

我是 Spring 新手，正在尝试开始使用 Neo4j 为开源网上商店构建 API。现在，我在从存储库中的自定义 @Query'ies 获取正确响应时遇到问题。

这是回复:

{
  "timestamp": 1422223603656,
  "status": 500,
  "error": "Internal Server Error",
  "exception": "java.lang.RuntimeException",
  "message": "Cannot extract single value from Iterable with more than one elements.",
  "path": "/api/v1/articles"
}

这是查询:

@Override
@Query("MATCH (a:`Article`)-[r:CATEGORIZED_TO]->() RETURN a.name as name, a.number as number, r.segment as segment")
Result<Article> findAll();

我以这种方式使用存储库:

@RequestMapping(value = "/articles", method = RequestMethod.GET)
public
@ResponseBody
Iterable<Article> list(
        @RequestParam(value = "segment", required = false) String segment
) {
    Iterable<Article> articles = null;

    Transaction tx = graphDatabase.beginTx();

    try {
        Result result = articleRepository.findAll();

        articles = result.as(Article.class);

        tx.success();
    } finally {
        tx.close();
    }

    return articles;
}

你能发现问题吗？

编辑:

这是 Article 类

@NodeEntity
public class Article {

  @GraphId
  private Long graphId;

  @GraphProperty
  private String name;

  @Indexed(unique = true)
  private String number;

  @RelatedTo(elementClass = Category.class, type = "BELONGS_TO", direction = Direction.OUTGOING)
  Set<Category> categories;

  @RelatedToVia(elementClass = Listing.class, type = "BELONGS_TO", direction = Direction.OUTGOING)
  Iterable<Listing> listings;

  public Article() {
  }

  public Article(String name, String number) {
    this.name = name;
    this.number = number;
  }

  public Long getGraphId() {
    return graphId;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public String getNumber() {
    return number;
  }

  public void setNumber(String number) {
    this.number = number;
  }

  public Collection<Category> getCategories() {
    return categories;
  }

  public Collection<Listing> getListings() {
    return IteratorUtil.asCollection(listings);
  }

}

Answer 1

您没有共享 Article 类的定义。

使用带有 @QueryResult 注释的 DTO 类，或者如果 Article 是您的域类，则必须返回

此外，Result DSL 上的正确方法是 .to(Article.class) 而不是 as() 后者用于投影到 Collection 。