@Entity
public class Person implements Serializable {

  private long uid;
  // ...

  @Id
  public long getUid() {
    return uid;
  }

  public void setUid(long uid) {
    this.uid = uid;
  }

  // ...
}

@Entity
@IdClass(PersonInfoId.class)
public class PersonInfo implements Serializable {
 
  private Person person;
  private String fieldName;
  private String value;

  @Id
  @ManyToOne
  public Person getPerson() {
    return person;
  }

  public void setPerson(Person person) {
    this.person= person;
  }

  @Id
  public String getFieldName() {
    return fieldName;
  }

  public void setFieldName(String fieldName) {
    this.fieldName= fieldName;
  }
 
  //...
}

@Embeddable
public class PersonInfoId implements Serializable {
 
  private Person person;
  private String fieldName;

  public Person getPerson() {
    return person;
  }

  public void setPerson(Person person) {
    this.person= person;
  }

  public String getFieldName() {
    return fieldName;
  }

  public void setFieldName(String fieldName) {
    this.fieldName= fieldName;
  }
 
  // override equals/hashCode
}

@Embeddable
public class PersonInfoId implements Serializable {
 
  private Person person;
  private String fieldName;

// HERE ---------------
  @ManyToOne
  public Person getPerson() {
    return person;
  }
...