JPA association class

Employee.java

import javax.persistence.*;
import java.util.Map;

@Entity
public class Employee {

    @GeneratedValue(strategy = GenerationType.AUTO)
    @Id
    @Column(name = "EMP_ID")
    private Integer id;

    @Column(name = "EMP_NAME")
    private String name;

    @ElementCollection
    @CollectionTable(name = "EMP_PROJECTS", joinColumns = @JoinColumn(name = "EMP_ID"))
    @MapKeyJoinColumn(name = "PROJECT_ID")
    private Map<Project, ProjectAllocation> currentProjects;

}

init-h2.sql

CREATE TABLE EMPLOYEE (
  EMP_ID INT NOT NULL GENERATED BY DEFAULT AS IDENTITY (START WITH 1),
  EMP_NAME VARCHAR (100) NOT NULL,
  PRIMARY KEY (EMP_ID)
);

CREATE TABLE PROJECT (
  PROJECT_ID INT NOT NULL GENERATED BY DEFAULT AS IDENTITY (START WITH 1),
  PRIMARY KEY (PROJECT_ID)
);

CREATE TABLE EMP_PROJECTS (
  EMP_ID INT NOT NULL,
  PROJECT_ID INT NOT NULL,
  PROJECT_COMMENT VARCHAR (200) NOT NULL,
  PROJECT_START_DATE DATE NOT NULL,
  PROJECT_END_DATE DATE NOT NULL,
  PROJECT_HOURS_PER_WEEK DOUBLE NOT NULL,
  PRIMARY KEY (EMP_ID, PROJECT_ID)
);

Project.java

import javax.persistence.*;

@Entity
public class Project {

    @GeneratedValue(strategy = GenerationType.AUTO)
    @Id
    @Column(name = "PROJECT_ID")
    private Integer id;

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Project)) {
            return false;
        }

        Project project = (Project) o;

        if (id != null ? !id.equals(project.id) : project.id != null) {
            return false;
        }

        return true;
    }

    @Override
    public int hashCode() {
        return id != null ? id.hashCode() : 0;
    }

}

ProjectAllocation.java

import javax.persistence.Column;
import javax.persistence.Embeddable;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import java.util.Date;

@Embeddable
public class ProjectAllocation {

    @Temporal(TemporalType.DATE)
    @Column(name = "PROJECT_START_DATE")
    private Date startDate;

    @Temporal(TemporalType.DATE)
    @Column(name = "PROJECT_END_DATE")
    private Date endDate;

    @Column(name = "PROJECT_COMMENT")
    private String comment;

    @Column(name = "PROJECT_HOURS_PER_WEEK")
    private Double hoursPerWeek;

}