How to set Entity with Foreign key parent to children using with springs, gradle, appengine, jpa, datanucleaus. - spring

Question

I have two entities: Country (parent) is the hardcoded entity, another one is a Place entity. It is a child entity (states, districts, mandal, villages).
Code below presents the child class.
import javax.jdo.annotations.Index;
import javax.jdo.annotations.Persistent;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
#Entity
public class Places {
#Id
#GeneratedValue
private Long id;
#Index
private String place_Name;
private String placeType;
#Persistent
#ManyToOne
private Country country;
public Country getCountry() {
return country;
}
public String getPlace_Name() {
return place_Name;
}
public void setPlace_Name(String place_Name) {
this.place_Name = place_Name;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public void setCountry(Country countryByName) {
this.country = countryByName;
}
public String getPlaceType() {
return placeType;
}
public void setPlaceType(String placeType) {
this.placeType = placeType;
}
}
Code below is parent entity (code).
package com.geeklabs.rss.domain;
import javax.jdo.annotations.Index;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
#Entity
public class Country {
#Id
#GeneratedValue
private Long id;
#Index
private String countryName;
private String countryCode;
public String getCountryName() {
return countryName;
}
public void setCountryName(String countryName) {
this.countryName = countryName;
}
public String getCountryCode() {
return countryCode;
}
public void setCountryCode(String countryCode) {
this.countryCode = countryCode;
}
public long getId() {
return id;
}
}
Below xml file is my persistence.xml
<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
<persistence-unit name="rss" transaction-type="RESOURCE_LOCAL">
<provider>org.datanucleus.api.jpa.PersistenceProviderImpl</provider>
<class>com.geeklabs.rss.domain.Country</class>
<class>com.geeklabs.rss.domain.Places</class>
<properties>
<property name="datanucleus.ConnectionURL" value="appengine"/>
<property name="datanucleus.NontransactionalRead" value="true"/>
<property name="datanucleus.NontransactionalWrite" value="true"/>
</properties>
</persistence-unit>
</persistence>
Using classes above I'm trying to assign parent id to child but I got exceptions.
How to assign the foreign key from parent to child using appengine, jpa, datanucleus, spring?