英文:
Hibernate and Jackson manyToMany relation with extra fields
问题
最近我一直在尝试通过多对多关系链接一个Module表和一个Activity表。这种关系引入了一个额外的字段，如下所示。
-------------------------------------------------------------| Module | ModuleHasActivities | Activities |-------------------------------------------------------------| id | Module_idModule | id || Name | Activity_idActivity | Name || Observations | Day | Price |-------------------------------------------------------------
我使用JsonManagedReference和JsonBackReference来避免无限循环。不幸的是，结果并不是预期的，因为我无法从activities获取到modules列表，反之亦然。返回的唯一信息是实体字段。
@Entity@Table(name = "Module")public class Module implements Serializable {@Id@GeneratedValue@Column(name = "idModule")private int id;// 其他字段加上getter和setter@OneToMany(mappedBy = "module", cascade = CascadeType.ALL)@JsonBackReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}
@Entity@Table(name = "Activite")public class Activite implements Serializable {@Id@GeneratedValue@Column(name = "idActivite")private int id;// 其他字段@OneToMany(mappedBy = "activite", cascade = CascadeType.ALL)@JsonBackReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}
@Entity@Table(name = "Module_has_Activite")public class ModuleHasActivities implements Serializable {@Id@ManyToOne@JoinColumn(name = "Module_idModule")@JsonManagedReferenceprivate Module module;@Id@ManyToOne@JoinColumn(name = "Activite_idActivite")@JsonManagedReferenceprivate Activite activite;@Column(name = "IdJour")private int jour;}
查询模块的响应：
[{"id": 1,"code": "TT1","title": "Test 1","description": "Nothing","observations": "Nothing"}]
我期望的结果（类似于这样）：
[{"id": 1,"code": "TT1","title": "Test 1","description": "Nothing","observations": "Nothing","activities": ["day1": {// activities的字段},"day2": {// activities的字段}]}]
当我调试Hibernate的SQL查询时，我们可以看到连接从未执行。这正是我所关心的！连接到模块表的连接丢失了。
对此有一点帮助将不胜感激，
谢谢
已访问链接:
Extra fields for many to many relations
英文:
Recently I've been trying to link a Module table and an Activity table by a Many to Many relationship.
This relation welcomes an additional field as below.
-------------------------------------------------------------| Module | ModuleHasActivities | Activities |-------------------------------------------------------------| id | Module_idModule | id || Name | Activity_idActivity | Name || Observations | Day | Price |-------------------------------------------------------------
I use JsonManagedReference and JsonBackReference to avoid infinite loops. Unfortunately the result is not the expected one since I don't get the list of modules from the activities and vice versa. The only information returned are the entity fields.
@Entity@Table(name = "Module")public class Module implements Serializable {@Id@GeneratedValue@Column(name = "idModule")private int id;// Other fields plus getter and setter@OneToMany(mappedBy = "module", cascade = CascadeType.ALL)@JsonBackReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}
@Entity@Table(name = "Activite")public class Activite implements Serializable {@Id@GeneratedValue@Column(name = "idActivite")private int id;// Other fields@OneToMany(mappedBy = "activite", cascade = CascadeType.ALL)@JsonBackReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}
@Entity@Table(name = "Module_has_Activite")public class ModuleHasActivities implements Serializable {@Id@ManyToOne@JoinColumn(name = "Module_idModule")@JsonManagedReferenceprivate Module module;@Id@ManyToOne@JoinColumn(name = "Activite_idActivite")@JsonManagedReferenceprivate Activite activite;@Column(name = "IdJour")private int jour;}
Query modules response:
[{"id": 1,"code": "TT1","title": "Test 1","description": "Nothing","observations": "Nothing",}]
What I expect (something like this) :
[{"id": 1,"code": "TT1","title": "Test 1","description": "Nothing","observations": "Nothing","activities": ["day1":{//fields of activities},"day2":{//fields of activities},]}]
When I debug hibernate's SQL queries, we see that the join is never done. And that's what interests me! Joints to the module table are missing.
A little help would be appreciated,
Thank you
Already visited links :
Extra fields for many to many relations
答案1
得分: 0
你需要理解 JsonManagedReference 和 JsonBackReference 之间的区别。详见：https://stackoverflow.com/a/37394318/607637。
@Entitypublic class Module {@JsonBackReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}@Entitypublic class ModuleHasActivities implements Serializable {@JsonManagedReferenceprivate Module module;}
在这里，如果你序列化 Module 对象，你的 JSON 中将不会包含 moduleHasActivities 字段，但是如果你序列化 ModuleHasActivities 对象，你将会得到 module 字段。
所以，解决方案是将 @JsonBackReference 和 @JsonManagedReference 进行调换，如下所示：
@Entitypublic class Module {@JsonManagedReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}@Entitypublic class ModuleHasActivities implements Serializable {@JsonBackReferenceprivate Module module;}
英文:
You need to understand the differences between JsonManagedReference and JsonBackReference. See this: https://stackoverflow.com/a/37394318/607637 for more info.
@Entitypublic class Module {@JsonBackReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}@Entitypublic class ModuleHasActivities implements Serializable {@JsonManagedReferenceprivate Module module;}
Here, if you serialize Module object, you will not get moduleHasActivities field in json but if you serialize ModuleHasActivities object you will get module field.
So, the solution is to flip the @JsonBackReference and @JsonManagedReference as below:
@Entitypublic class Module {@JsonManagedReferenceprivate Set<ModuleHasActivities> moduleHasActivities = new HashSet<>();}@Entitypublic class ModuleHasActivities implements Serializable {@JsonBackReferenceprivate Module module;}
答案2
得分: 0
终于，我解决了我的问题。我不再使用复合键，而是将我的数据库模型更改为使用主 id 键和两个指向我关注的表的引用。映射更简单，我可以获取到所需信息。
英文:
Finally, I solved my problem. Instead of using a composite key, I changed my database model to use a primary id key and 2 references to my concerned tables. Mapping is easier and I get my information.
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