三个实体类的一对多和多对一映射中的问题

Question

I have three entity classes Country , State , and City . Now I am trying to display the cities that come under a particular state and states that come under a particular country. but I am facing an error like

org.springframework.dao.DataAccessResourceFailureException:
Could not create JPA EntityManager;
nested exception is org.hibernate.AnnotationException:
@OneToOne or @ManyToOne on com.region.model.State.cities reference
an unknown entity: java.util.List. 

Please help me out in one-to-many and many-to-one mapping for the three tables.

package com.region.model;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.SecondaryTable;
import javax.persistence.Table;
import javax.persistence.Transient;

import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonManagedReference;
@Entity
@Table(name = "country")
public class Country {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column
    private Integer country_id;
    @Column
    private String country_name;
//  @Column
//  private String status="active";
    @Transient
    private String statusCode;
    @Transient
    private String statusmessage;
    
    @OneToMany(targetEntity=State.class, mappedBy="country",cascade=CascadeType.ALL, fetch = FetchType.LAZY)    
     @JsonBackReference
    private List<State> states;
    public Country() {

    }
    public Integer getCountry_id() {
        return country_id;
    }

    public void setCountry_id(Integer country_id) {
        this.country_id = country_id;
    }

    public String getCountry_name() {
        return country_name;
    }
    public void setCountry_name(String country_name) {
        this.country_name = country_name;
    }
//  public String getStatus() {
//      return status;
//  }
//  public void setStatus(String status) {
//      this.status = status;
//  }
    public String getStatusCode() {
        return statusCode;
    }
    public void setStatusCode(String statusCode) {
        this.statusCode = statusCode;
    }
    public String getStatusmessage() {
        return statusmessage;
    }
    public void setStatusmessage(String statusmessage) {
        this.statusmessage = statusmessage;
    }

    public List<State> getStates() {
        return states;
    }

    public void setStates(List<State> states) {
        this.states = states;
    }
    
}

package com.region.model;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import javax.persistence.Transient;
import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonManagedReference;
@Entity
@Table(name = "state")
public class State {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column
    private Integer sk_state_id;
    @Column
    private String state_name;
    @Column
    private String country_id;
//  @Column
//  private String status="active";
    @Transient
    private String statusCode;
    @Transient String statusMessage;    
    @ManyToOne()
    @JoinColumn(name="country_id", referencedColumnName = "country_id", insertable = false, updatable = false)    
    @JsonManagedReference
    @OneToMany(targetEntity=City.class, mappedBy="state",cascade=CascadeType.ALL, fetch = FetchType.LAZY)    
    private List<City>cities;
    private Country country;
    public State() {
    }
    public Integer getSk_state_id() {
        return sk_state_id;
    }
    public void setSk_state_id(Integer sk_state_id) {
        this.sk_state_id = sk_state_id;
    }
    public String getState_name() {
        return state_name;
    }
    public void setState_name(String state_name) {
        this.state_name = state_name;
    }
    public String getCountry_id() {
        return country_id;
    }
    public void setCountry_id(String country_id) {
        this.country_id = country_id;
    }
//  public String getStatus() {
//      return status;
//  }
//  public void setStatus(String status) {
//      this.status = status;
//  }
    public String getStatusCode() {
        return statusCode;
    }
    public void setStatusCode(String statusCode) {
        this.statusCode = statusCode;
    }
    public String getStatusMessage() {
        return statusMessage;
    }
    public void setStatusMessage(String statusMessage) {
        this.statusMessage = statusMessage;
    }
    public Country getCountry() {
        return country;
    }
    public void setCountry(Country country) {
        this.country = country;
    }
    public List<City> getCities() {
        return cities;
    }
    public void setCities(List<City> cities) {
        this.cities = cities;
    }
    
    
}

package com.region.model;
import java.lang.annotation.Repeatable;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.OneToOne;
import javax.persistence.Table;
import javax.persistence.Transient;
import com.fasterxml.jackson.annotation.JsonBackReference;
import com.fasterxml.jackson.annotation.JsonManagedReference;
@Entity
@Table(name = "city")
public class City {
    
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column
    private Integer sk_city_id;
    @Column
    private String city_name;
    @Column
    private String state_id;
    @Column
    private String country_id;
    @Transient
    private String statusCode;
    @Transient
    String statusMessage;
    @ManyToOne(targetEntity = State.class)
    @JoinColumn(name="state_id", referencedColumnName ="sk_state_id", insertable = false, updatable = false)    
    private State state;
    private Country country;
    //private List<State>states;
    public City() {
        }
    public Integer getSk_city_id() {
        return sk_city_id;
    }
    public void setSk_city_id(Integer sk_city_id) {
        this.sk_city_id = sk_city_id;
    }
    public String getCity_name() {
        return city_name;
    }
    public void setCity_name(String city_name) {
        this.city_name = city_name;
    }
    public String getState_id() {
        return state_id;
    }
    public void setState_id(String state_id) {
        this.state_id = state_id;
    }
    public String getCountry_id() {
        return country_id;
    }
    public void setCountry_id(String country_id) {
        this.country_id = country_id;
    }
    public String getStatusCode() {
        return statusCode;
    }
    public void setStatusCode(String statusCode) {
        this.statusCode = statusCode;
    }
    public String getStatusMessage() {
        return statusMessage;
    }
    public void setStatusMessage(String statusMessage) {
        this.statusMessage = statusMessage;
    }
    public Country getCountry() {
        return country;
    }
    public void setCountry(Country country) {
        this.country = country;
    }
    public State getState() {
        return state;
    }
    public void setState(State state) {
        this.state = state;
    }
    
    @Override
    public String toString() {
        return "City [sk_city_id=" + sk_city_id + ", city_name=" + city_name + ", state_id=" + state_id
                + ", country_id=" + country_id + ", statusCode=" + statusCode + ", statusMessage=" + statusMessage
                + "]";
    }
//  public List<State> getStates() {
//      return states;
//  }
//  public void setStates(List<State> states) {
//      this.states = states;
//  }
    
    
}

Answer 1

mappedBy is only used once in a relationship between 2 classes, for the class that you want to define the relationship for both. So in the class Countries you probably don't need mappedBy at all, in the class Cities, you should put mappedBy="state", and in the class State it would make sense to put mappedBy="country"