How can achieve strong consistency of Entity without parent in JDO for datastore

Question

Here is my simple entity:

import com.google.appengine.api.datastore.Key;

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@PersistenceCapable 

public class Food {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key id;
    @Persistent
    private String name;
    @Persistent
    private String description;
    public Key getId() {
        return (id);
    }
    public void setId(Key id) {
        this.id = id;
    }
    public String getName() {
        return (name);
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return (description);
    }
    public void setDescription(String description) {
        this.description = description;
    }
}

And I'm loading my foods List this way:

try {
            pm = PMF.get().getPersistenceManager();
            Query q = pm.newQuery(Food.class);
            foods = (List<Food>) q.execute();
        } catch (Exception exc) {
            exc.printStackTrace();
        }
        finally {
            pm.close();
        }

The Key is automatically generated for every Food entity. I'm using also HRD. So... the query above (pm.newQuery(Food.class);) is not with strong consistency and one time is returning all results , second time is not returning the newly created foods. How to change this query in such way, that every time I get all foods from the database. In datastore documentation I've read that should be ancestor query, but I don't have ancestor path. (I should say that I'm new in datastore and still learning from yesterday but this one took me to much time). Please help me.

You can't achieve strong consistency without using a parent. That's the whole point. Either you use ancestors, or you accept that sometimes your query results will be stale (and use eg memcache to get around that). — Daniel Roseman

voscausa voscausa · Accepted Answer · 2014-02-13T01:17:35

Two excellent and easy to understand video's about the workings of the App engine datastore and strong consistency:

Part-1: Datastore Introduction

https://www.youtube.com/watch?v=fQazhzcC-rg

Part-2: Datastore Query, Index and Transaction

https://www.youtube.com/watch?v=d4CiMWy0J70#t=645

How can achieve strong consistency of Entity without parent in JDO for datastore

2 Answers