How to store list of values in datastore

[Deepak Singh]

Hi,

I am using GAE 1.5.4 JAVA.

public class Citynames implements Serialisable{

   String id;

    String name;

   // getter setter

}

I have a list of city names contained in an arraylist,

ArrayList<String> list = new ArrayList<String>();

for(........)  { 

Citynames city = new Citynames();

city.add("11");

city.add(""ddd);

list.add(city);

}

Now i need to store this list in datastore.

What is the best way to acheive this as 

datastore.put(list) is not working and fails with following exception 

Citynames is not a supported property type.

Thanks

Deepak

[Deepak Singh]

Anyone can help on this...

[Ronoaldo José de Lana Pereira]

Hi Deepak,

You may be interested on the Storing Data part of the documentation.  It explains how the Datastore works and how you can use the raw Entity class to store data. This is the "low level datastore" way to persist your data:

Entity e = new Entity("Citynames");

e.setProperty("name", "Name of the City");

DatastoreServiceFactory.getDatastoreService().put(e);

This is not the usual way to store Java objects, but is the raw way. I recomend you to look at Objectify documentation, probrably the greatest persistency layer for appengine out there.

Hope this helps.

Best Regards,

-Ronoaldo

[Deepak Singh]

Hi Ronoaldo,

This is fine. But i want to store the arraylist directly to datastore.

So 

Entity e = new Entity("Citynames");

e.setProperty("name", list);

DatastoreServiceFactory.getDatastoreService().put(e);

How is the above functionality possible?

2011/9/15 Ronoaldo José de Lana Pereira <rper...@beneficiofacil.com.br>

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[Ronoaldo José de Lana Pereira]

Hi Deepak,

The datastore supports Collections as a property for an Entity. To the BigTable, this is a "list property", I.E, a multi-value field in one row in the datastore. It is fine to add a list of names, i.e.:

Entity e = new Entity("Citynames");

e.setProperty("name", Collections.asList("name1", "name2", "name3'));

DatastoreServiceFactory.getDatastoreService().put(e);

This will create en entry in the datastore with "Citynames" as kind, and with a property called "name" with the tree values in the list. You may find more info about what can be stored in an Entity property here, and a few notes about too many values on the same property of an entity here.

Hope this helps,

- Ronoaldo

[Deepak Singh]

Thanks Ronoaldo. I got it now.

2011/9/15 Ronoaldo José de Lana Pereira <rper...@beneficiofacil.com.br>

Hi Deepak,

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