Java 日食线+；JPA@OneToOne-链接缺失

我目前正在与EclipseLink和MongoDB合作。我有一个案例，其中我有一个@OneToOne映射。以下是守则-

    //Parent.java
    @Entity
    @NoSql(dataFormat = DataFormatType.MAPPED)
    public class Parent {
        @Id
        @GeneratedValue
        @Field(name = "_id")
        private String id;
        private String parentName;

        @OneToOne(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY)
        private Child  child;

        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
    }

        public String getParentName() {
           return parentName;
       }

        public void setParentName(String parentName) {
           this.parentName = parentName;
        }

    public Child getChild() {
        return child;
    }

    public void setChild(Child child) {
        this.child = child;
    }

    }

    //Child.java


    @Entity
    @NoSql(dataFormat = DataFormatType.MAPPED)
    public class Child {
    @Id
    @GeneratedValue
    @Field(name = "_id")
    private String id;

    private String childName;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getChildName() {
        return childName;
    }

    public void setChildName(String childName) {
        this.childName = childName;
    }

}

对于上述类，我按照以下顺序持久化了对象

Parent parent = new Parent();
parent.setParentName("pname");

// Create
System.out.println("***************  Persisting *****************");

Child child = new Child();
child.setChildName("cname");
daoService.createChild(child);

Parent p = daoService.createParent(parent);

p.setChild(child);
daoService.updateEntity(p);

Parent parent2 = daoService.readParent(p.getId());

 System.out.println("Child : " + parent2.getChild());

 Child c = daoService.readChild(parent2.getChild().getId());
 System.out.println("Child id : " + c.getId());

但是，我看到在MongoDB中，父对象和子对象之间没有链接

在持久化步骤之后，MongoDB的BSON结构如下所示

{
  "_id" : "53C67031BBD8A5FDA924868D",
  "PARENTNAME" : "pname",
  "CHILD__id" : null
}

{
  "_id" : "53C67031BBD8A5FDA924868C",
  "CHILDNAME" : "cname"
}

谁能告诉我，我在这里做错了什么