Using JPA #ElementCollection for a String collection from a join table? - jpa

Question

I would like my User entity to include a List<String> of permissions coming from user_permission join table, however getting a multitude of errors using different examples.
Should ElementCollection also be able to handle join table as defined below given I indicate which columns to join?
user table
id (pk)
email
permission table
permission (pk)
permission_description
user_permission table
email (fk, pk)
permission (fk, pk)
User Entity
#ElementCollection
#Column(name="permission", nullable=false)
#CollectionTable(name = "user_permission", joinColumns = #JoinColumn(name = "email", referencedColumnName = "email"))
private List<String> permissions = new ArrayList<String>();
Error:
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.security.authentication.InternalAuthenticationServiceException: class com.abc.data.entity.User cannot be cast to class java.io.Serializable (com.abc.data.entity.User is in unnamed module of loader 'app'; java.io.Serializable is in module java.base of loader 'bootstrap')
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:523) ~[jakarta.servlet-api-4.0.3.jar:4.0.3]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.6.RELEASE.jar:5.2.6.RELEASE]

Answer 1

The issue was the join column, which in this case was email, which was not an ID on the User table.
When the user_permission table was altered to include the user ID instead of user email, and join table name modified accordingly, it works.
Working Example
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
private int accountId;
private String name;
private String email;
private String password;
private boolean admin;
#ElementCollection
#Column(name="permission", nullable=false)
#CollectionTable(name = "user_permission", joinColumns = #JoinColumn(name = "user_id", referencedColumnName = "id"))
private List<String> permissions = new ArrayList<String>();