JPA Composite PK referenced by FKs in One to Many Relationship - spring

Question

I am trying to map the tables below into JPA. The relationships are one-to-many between user_tax and tax and user_tax and user. It has confused me the fact that i have a composite primary key, and i need to map the foreign keys to these 2 keys.
the error message: org.hibernate.AnnotationException: mappedBy reference an unknown target entity property: entity.Tax.user_tax in entity.UserTax.taxs
tax user_tax user
-------- -------- ------
PK|t_id |--------| t_id |PK-FK |u_name|
|t_name| PK-FK| u_id |-------|u_id | PK
| | | name | | |
Here is my Entities:
#Entity
#Table(name = "user")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class User implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name="u_name")
private String uname;
getters + setters
}
#Entity
#Table(name = "tax")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Tax implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "t_name")
private String tname;
#Embeddable
public class UserTaxId implements Serializable {
#Column(name="u_id")
private Long uId;
#Column(name="t_id")
private Long tId;
#Entity
#Table(name = "user_tax")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class UserTax implements Serializable {
#EmbeddedId
private UserTaxId userTaxId;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "user_tax")
private List<User> users;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "user_tax")
private List<Tax> taxs;

Answer 1

Your 1:n mappings are backwards (i.e. a UserTax can have only a single User and a single Tax) and you are using a derived identity. Try mapping UserTax like this:
#Entity
#Table(name = "user_tax")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class UserTax implements Serializable {
#EmbeddedId
private UserTaxId userTaxId;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("uId") // maps uId attribute of embedded id
private User user;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("tId") // maps tId attribute of embedded id
private Tax tax;
...
}
Derived identities are discussed (with examples) in the JPA 2.2 spec in section 2.4.1.

Answer 2

I will post here what worked for me after 3 days of research.
Brian Vosburgh correctly posted the UserTax class:
#Entity
#Table(name = "user_tax")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class UserTax implements Serializable {
#EmbeddedId
private UserTaxId userTaxId;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("uId") // maps uId attribute of embedded id
private User user;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("tId") // maps tId attribute of embedded id
private Tax tax;
...
}
However, i was getting error meassages and my code wasn't compiling. Then i also had to edit the User and Tax classes:
#Entity
#Table(name = "user")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class User implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToMany(
mappedBy = "tid",
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<UserTax> tax = new ArrayList<>();
#Column(name="u_name")
private String uname;
getters + setters
}
#Entity
#Table(name = "tax")
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Tax implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToMany(
mappedBy = "uid",
cascade = CascadeType.ALL,
orphanRemoval = true
)
private List<UserTax> taxs = new ArrayList<>();
#Column(name = "t_name")
private String tname;
setters+getters
}
Here is the link where i found the solution to my problem: https://vladmihalcea.com/the-best-way-to-map-a-many-to-many-association-with-extra-columns-when-using-jpa-and-hibernate/