具有嵌套属性的 JPA MapKey

Question

I have 3 elements like this:

public class ItemType {
  @Id
  private Long id = null;
  ...
  @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true, mappedBy = "itemTypeVO")
  @MapKey(name = "company.id")
  private Map<Long, ItemTypePurpose> purposeHash = null;
  ...
}


public class ItemTypePurpose {
  @Id
  private Long id = null;
  ...
  @ManyToOne(fetch = FetchType.LAZY, optional = false)
  @JoinColumn(name = "idcompany")
  private Company company = null;
  ...
}

public class Company {
  @Id
  private Long id = null;
  ...
}

My problem is, I want the ID of Company as key of my map inside ItemType .

I can compile and deploy the application without any errors. Can persist ItemType, and everything goes well to DB. But when I get it back, the Map key is "wrong", I don't know what information is being used, but for sure it's not the Company id. Perhaps the ItemTypePurpose's ID.

The Company is being loaded into Map correctly, just the map key is wrong. I've tryied to google, bu can't find anything. Does any way to JPA create my map with this "nested attribute"?

*Sorry about my english, feel free if you understand what I need and can do a better writing in english to edit my question.

Answer 1

This doesn't exactly solves the question, but solve my needs for now.

Since que ID of Company was in table of ItemTypePurpose, I could change the MapKey to:

public class ItemType {
  @Id
  private Long id = null;
  ...
  @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true, mappedBy = "itemTypeVO")
  @MapKeyColumn(name = "idcompany", insertable = false, updatable = false)
  private Map<Long, ItemTypePurpose> purposeHash = null;
  ...
}

Instead of @MapKey, I used @MapKeyColumn. The @MapKeyColumn(name = "idcore_company", insertable = false, updatable = false is to turn the "Key Information" ReadOnly and avoid mapping conflict, since the same column is used in ItemTypePurpose to map the Entity.

Not exactly an answer, but "worked around" to solve my needs. This solution does not cover if you want a field as Map Key other than the ID.

Answer 2

Late reply, but can be helpful to someone else.

@MapKeyColumn seems to be the official solution here. As per the documentation, it seems the annotation to be used depends on the key type of the Map, regardless of the mapped fields. In your case, the key type is a Long , hence below will apply:

https://docs.oracle.com/cd/E19226-01/820-7627/giqvn/index.html

Using Map Collections in Entities

Collections of entity elements and relationships may be represented by java.util.Map collections. A Map consists of a key and value.

If the key type of a Map is a Java programming language basic type, use the javax.persistence.MapKeyColumn annotation to set the column mapping for the key. By default, the name attribute of @MapKeyColumn is of the form RELATIONSHIP FIELD/PROPERTY NAME_KEY. For example, if the referencing relationship field name is image, the default name attribute is IMAGE_KEY.

In summary: For nested fields go for MapKeyColumn(name="myNestFiled_key"), then you will set the value manually in your code like:

ItemType.getPurposeHash().put(ItemTypePurpose.getCompany().getId(), ItemTypePurpose);