How to get all the kinds in the google app engine

Question

I'm using java to code for GAE, I've read through the GAE Java low level API and can't find any answer to my question yet.

I wanna know if there's a way where I can call a method/do a JDOPL and it returns all the different kinds of entities in my Datastore.

Answer 1

You can use the Metadata API. For example:

Query query = new Query(Entities.KIND_METADATA_KIND);
DatastoreService datastoreService = DatastoreServiceFactory.getDatastoreService();

Iterable<Entity> entityIterable = datastoreService.prepare(query).asIterable();

for(Entity entity : entityIterable) {
    System.out.println("Entity kind: " + entity.getKey().getName());
}

Answer 2

You could use the datastore statistics API:

http://code.google.com/appengine/docs/java/datastore/stats.html

It looks like the __Stat_Kind__ statistic will give you the info you want.

Answer 3

I found a working solution here. (it doesn't work in local deployment server as of July 9, 2010)

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
PreparedQuery global = datastore.prepare(new Query("__Stat_Kind__"));

for( Entity globalStat : global.asIterable() )
{
    Long totalBytes = (Long) globalStat.getProperty("bytes");
    Long totalEntities = (Long) globalStat.getProperty("count");
    String kindName = (String) globalStat.getProperty("kind_name");
    resp.getWriter().println("[" + kindName + "] has " + totalEntities + " entities and takes up " + totalBytes + "bytes<br/>");
}