java - 意外的空值，neo4j

Question

我不知道为什么我无法获取movie字段的值。我调试了它，发现movie为空。我发个图你就看到了 。请给我一些建议。我确信我已经成功地建立了这种关系，可能推荐有问题。类还是密码？

public interface MovieRepository extends GraphRepository<Movie> {


@Query("match (user:User {login: {0}})-[r:RATED]->(movie)<-[r2:RATED]-(other)-[r3:RATED]->(otherMovie) "
        + " where r.stars >= 3 and r2.stars >= r.stars and r3.stars >= r.stars "
        + " with otherMovie, avg(r3.stars) as rating, count(*) as cnt" 
        + " order by rating desc, cnt desc"
        + " return otherMovie as movie, rating limit 10")
List<MovieRecommendation> getRecommendations(String login);

}

推荐.class

@QueryResult
public class MovieRecommendation {


Movie movie;
int rating;
public Movie getMovie() {
    return movie;
}
public void setMovie(Movie movie) {
    this.movie = movie;
}
public int getRating() {
    return rating;
}
public void setRating(int rating) {
    this.rating = rating;
   }
}

Controller

@RequestMapping(value = "/user", method = RequestMethod.GET)
public String profile(Model model, HttpServletRequest request) {

    HttpSession session = request.getSession(false);
    User user = (User) session.getAttribute("user");
    model.addAttribute("user", user);

    if (user != null) {
        List<MovieRecommendation> mr = movieRepository.getRecommendations(user.getLogin());
    MovieRecommendation movie = new MovieRecommendation();
    Movie m = new Movie();
    m.setTitle("AA");
    movie.setMovie(m);
    mr.add(movie);
    model.addAttribute("recommendations", mr);
    }
    return "user/index";
}

使用 neo4j-community 运行 cypher

match (user:ollie)-[r:RATED]->(movie)<-[r2:RATED]-(other)-[r3:RATED]->(otherMovie) 
where r.stars >= 1 and r2.stars >= r.stars and r3.stars >= r.stars 
with otherMovie, avg(r3.stars) as rating, count(*) as cnt
order by rating desc, cnt desc
return otherMovie limit 10

Answer 1

我认为您的查询返回 null。

所以第一个元素 [0] 有一个为 null 的电影...

电影“AA”应该位于数组中的 [1] 中，因为您进行了查询，并在查询后附加了推荐