獲取已分離的實體以@ManyToMany雙向關係持續存在

我無法使用JPA與多對多關係（雙向）持久存在實體。下面是示例代碼：獲取已分離的實體以@ManyToMany雙向關係持續存在

@Entity 
@Table(name = "aentity") 
public class AEntity { 
    @Id 
    @Column(name = "id", 
      unique = true) 
    @TableGenerator(initialValue = 1, 
      name = "aentity_id_generator", 
      pkColumnName = "table_name", 
      pkColumnValue = "aentity", 
      table = "id_generator", 
      valueColumnName = "id") 
    @GeneratedValue(generator = "aentity_id_generator", 
      strategy = GenerationType.TABLE) 
    private BigInteger id; 

    @JoinTable(name = "bentity_aentities") 
    @ManyToMany 
    private Set<BEntity> bentities; 

    /* getters and setters follows */ 
} 

@Entity 
@Table(name = "bentity") 
public class BEntity { 
    @Id 
    @Column(name = "id", 
      unique = true) 
    @TableGenerator(initialValue = 1, 
      name = "bentity_id_generator", 
      pkColumnName = "table_name", 
      pkColumnValue = "bentity", 
      table = "id_generator", 
      valueColumnName = "id") 
    @GeneratedValue(generator = "bentity_id_generator", 
      strategy = GenerationType.TABLE) 
    private BigInteger id; 

    @ManyToMany(mappedBy = "bentities") 
    private Set<AEntity> aentities; 

    /* getters and setters follows */ 
}

下面是DTO到實體轉換器...

public class DtoToEntityConverter { 
    public void convertToEntity(AEntityDto aDto, AEntity a) { 
     a.setBEntities(aDto.getBEntities().parallelStream(). 
     .map(bDto -> { 
      return toBEntity(bDto); //this will just copy/transfer the properties from bEntityDto to bEntity. 
     }) 
     .collect(Collectors.toSet())); 
    } 
}

方案1：保存與AEntity BEntity（ID = NULL） - OK

方案2 ：使用現有的BEntity（id = id，存在於db中）保存AEntity

場景2中發生以下異常：在stackoverflo尋找相同的問題w並嘗試了不同的組合和建議，但沒有鎖定。

detached entity passed to persist: BEntity; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: BEntity"

任何人都可以幫忙。謝謝。

來源

2016-11-27 imprezzeb

你可以試試...

在第二個實體：

@ManyToMany(cascade=CascadeType.ALL, mappedBy="bentities") 
private Set<AEntity> aentities;

在第一個實體：

@ManyToMany(cascade=CascadeType.ALL) 
@JoinTable(name="bentity_aentities", [email protected](name="aentity_id"), [email protected](name="bentity_id")) 
private Set<BEntity> bentities;

來源

2016-11-27 16:49:16 Aniru

謝謝你的迴應，但擁有實體應該是AEntity，沒有「mappedBy」的那個，所以上面的代碼在這種情況下是不合適的，因爲弱實體（具有mappedBy的實體）沒有能力保存/更新擁有實體（在你的情況下是BEntity）。 – imprezzeb

終於解決了我的問題。這是DTO到實體轉換器（我的壞）的問題。

上一頁轉換器：

public AEntity toAEntity(@NotNull AEntityDto aentityDto) { 
    AEntity aentity = new AEntity(); 
    copyProperties(aentityDto, aentity); 
    return aentity; 
}

重構轉換器：返回現有實體的引用。

public AEntity toAEntity(@NotNull AEntityDto aentityDto) { 
    AEntity aentity = aRepository.findSingleByTitle(aentityDto.getTitle()); 
    if(aentity == null) { 
     aentity = new AEntity(); 
     copyProperties(aentityDto, aentity); 
    } 
    return aentity; 
}

謝謝。

來源

2016-11-28 06:18:28 imprezzeb

獲取已分離的實體以@ManyToMany雙向關係持續存在

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