JPA OneToMany，在控制台或Webapp中打印时如何忽略字段ManyToOne

时间：2018-12-21 20:41:57

标签： java spring-boot jpa

我有2个表格：流派（流派ID，流派名称）和电影（电影ID，电影名称，电影得分，流派ID）。 genre_id_fk，来自流派中针对genre_id的电影。

@Entity
@Table(name = "genres", schema = "test")
public class Genre {

@Id
@Column(name = "genre_id")
private int id;
@Column(name = "genre_name")
private String name;
@OneToMany(mappedBy = "genre", fetch = FetchType.LAZY)
private List<Movie> movies = new ArrayList<>();
}

和电影的第二实体

@Entity
@Table(name = "movies", schema = "test")
public class Movie {

@Id
@GeneratedValue
@Column(name = "movie_id")
private int id;
@Column(name = "movie_name")
private String name;
@Column(name = "movie_score")
private double score;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "genre_id")
private Genre genre;
}

当我尝试使用以下代码在控制台中打印它时：

public static void main(String[] args) {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu");
    EntityManager em = emf.createEntityManager();
    Genre genre = em.find(Genre.class, 1);
    System.out.println(genre);
}

接收Exception in thread "main" java.lang.StackOverflowError 只有从电影类字段“类型”中的toString（）中删除才能解决此问题。但是有可能避免吗？ Spring Boot应用程序也有同样的问题

@RestController
public class GenreController {

@Autowired
private GenreService genreService;

@RequestMapping("/test/{id}")
public List<Genre> getGenreInfo(@PathVariable int id){
    return genreService.getGenreFilms(id);
}
}

此处服务

@Service
public class GenreService {

public List<Genre> getGenreFilms(int id){
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("pu");
    EntityManager em = emf.createEntityManager();
    List<Genre> genres = new ArrayList<>();
    Genre genre = em.find(Genre.class, id);
    genres.add(genre);
    return genres;
}
}

，并收到如下问题： [{“ id”：1，“名称”：“惊悚片”，“电影”：[{“ id”：1，“名称”：“还好吗？”，“得分”：5.45，“类型” ：{“ id”：1，“名称”：“惊悚片”，“电影”：[{“ id”：1，“名称”：“还好吗？”，“得分”：5.45，“类型” ：{“ id”：1，“名称”：“惊悚片”，“电影”：[{“ id”：1，“名称”：“还好吗？”，“得分”：5.45，“类型” ：.... 并以无穷大作为例外。控制台我可以通过忽略toString（）方法中的字段来解决。但是如何在Web应用程序中解决此问题？

此处在控制台打印时休眠调试日志

22:15:37.154 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - 
Resolving associations for [com.company.Genre#1]
22:15:37.164 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done 
materializing entity [com.company.Genre#1]
22:15:37.164 [main] DEBUG 
org.hibernate.resource.jdbc.internal.ResourceRegistryStandardImpl - 
HHH000387: ResultSet's statement was not registered
22:15:37.165 [main] DEBUG 
org.hibernate.loader.entity.plan.AbstractLoadPlanBasedEntityLoader - Done 
entity load : com.company.Genre#1
22:15:37.165 [main] DEBUG 
org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl - 
Initiating JDBC connection release from afterTransaction
22:15:37.167 [main] DEBUG org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer 
- Loading collection: [com.company.Genre.movies#1]
22:15:37.167 [main] DEBUG org.hibernate.SQL - select movies0_.genre_id as 
genre_id4_1_0_, movies0_.movie_id as movie_id1_1_0_, movies0_.movie_id as 
movie_id1_1_1_, movies0_.genre_id as genre_id4_1_1_, movies0_.movie_name as 
movie_na2_1_1_, movies0_.movie_score as movie_sc3_1_1_ from test.movies 
movies0_ where movies0_.genre_id=?
Hibernate: select movies0_.genre_id as genre_id4_1_0_, movies0_.movie_id as 
movie_id1_1_0_, movies0_.movie_id as movie_id1_1_1_, movies0_.genre_id as 
genre_id4_1_1_, movies0_.movie_name as movie_na2_1_1_, movies0_.movie_score 
as movie_sc3_1_1_ from test.movies movies0_ where movies0_.genre_id=?
22:15:37.168 [main] DEBUG 
org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - 
Preparing collection intializer : [com.company.Genre.movies#1]
22:15:37.170 [main] DEBUG 
org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - 
Starting ResultSet row #0
22:15:37.171 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerIm 
pl - Found row of collection: [com.company.Genre.movies#1]
22:15:37.171 [main] DEBUG 
org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - 
Starting ResultSet row #1
22:15:37.172 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerIm 
pl - Found row of collection: [com.company.Genre.movies#1]
22:15:37.172 [main] DEBUG 
org.hibernate.loader.plan.exec.process.internal.ResultSetProcessorImpl - 
Starting ResultSet row #2
22:15:37.172 [main] DEBUG org.hibernate.loader.plan.exec.process.internal.CollectionReferenceInitializerIm 
pl - Found row of collection: [com.company.Genre.movies#1]
22:15:37.172 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - 
Resolving associations for [com.company.Movie#1]
22:15:37.172 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done 
materializing entity [com.company.Movie#1]
22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - 
Resolving associations for [com.company.Movie#2]
22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done 
materializing entity [com.company.Movie#2]
22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - 
Resolving associations for [com.company.Movie#3]
22:15:37.173 [main] DEBUG org.hibernate.engine.internal.TwoPhaseLoad - Done 
materializing entity [com.company.Movie#3]
22:15:37.173 [main] DEBUG 
org.hibernate.engine.loading.internal.CollectionLoadContext - 1 collections 
were found in result set for role: com.company.Genre.movies
22:15:37.173 [main] DEBUG 
org.hibernate.engine.loading.internal.CollectionLoadContext - Collection 
fully initialized: [com.company.Genre.movies#1]
22:15:37.173 [main] DEBUG 
org.hibernate.engine.loading.internal.CollectionLoadContext - 1 collections 
initialized for role: com.company.Genre.movies
22:15:37.173 [main] DEBUG 
org.hibernate.resource.jdbc.internal.ResourceRegistryStandardImpl - 
HHH000387: ResultSet's statement was not registered
22:15:37.173 [main] DEBUG org.hibernate.loader.collection.plan.AbstractLoadPlanBasedCollectionInitializer 
- Done loading collection
Exception in thread "main" java.lang.StackOverflowError

告诉我我在哪里做错了，以及如何解决或使用Google搜索此问题？只是不通过localhost：8080 / genre / id打印此对象？做一些特别的印刷品或什么？

1 个答案:

答案 0 :(得分：2)

在尝试toString的{​​{1}}实体时，您似乎有无限递归。您的代码首先按ID加载您的流派实体，然后调用Genre。因为您与Genre.toString()有@OneToMany关系，所以它与列表Movie保持联系，然后为与该流派相关的每部电影调用lazy loads。然后，对于每部电影，您都与流派有Movie.toString()的关系。问题就在这里。它将为列表中的每个电影再次调用@ManyToOne。

可能的解决方案

  1. 如果您只想在控制台中简单地打印它，请不要在Genre.toString()中加入电影列表
  2. 如果您正在使用Jackson，请将Genre.toString()添加到@JsonBackReference中的@ManyToOne关系中，这样Jackson映射到Json时将忽略它 Annotation documentation here
  3. 如果使用DTO，则不要在DTO中包括Movie属性。

希望这会有所帮助。

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