如何在命名空间之间复制数据存储实体

multitenancy

appengine-mapreduce getting started guides

__Stat_Kind__

import java.util.logging.Logger;

import org.apache.hadoop.io.NullWritable;

import com.google.appengine.api.NamespaceManager;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.tools.mapreduce.AppEngineMapper;

public class DatastoreCopyMapper extends
        AppEngineMapper<Key, Entity, NullWritable, NullWritable> {

    private static final Logger log = Logger
            .getLogger(DatastoreCopyMapper.class.getName());
    private static String destination;

    public DatastoreCopyMapper() {
    }

    @Override
    public void taskSetup(Context context) {
        log.warning("Doing per-task setup");
        destination = context.getConfiguration().get("destination");
        log.warning("destination: " + destination);
    }

    @Override
    public void map(Key key, Entity value, Context context) {

        NamespaceManager.set(destination);
        String name = key.getName();
        long id = key.getId();
        Key destinationKey = null;
        if (name != null) {
            destinationKey = KeyFactory.createKey(key.getKind(), name);
        } else if (id != 0) {
            destinationKey = KeyFactory.createKey(key.getKind(), id);
        }
        Entity destinationEntity = new Entity(destinationKey);
        destinationEntity.setPropertiesFrom(value);
        DatastoreService datastore = DatastoreServiceFactory
                .getDatastoreService();

        datastore.put(destinationEntity);

    }
}

<configurations>
  <configuration name="Copy between namespaces">
    <property>
      <name>mapreduce.map.class</name>
      <value>com.mysite.server.DatastoreCopyMapper</value>
    </property>
    <property>
      <name>mapreduce.inputformat.class</name>
      <value>com.google.appengine.tools.mapreduce.DatastoreInputFormat</value>
    </property>
    <property>
      <name human="Entity Kind to Map Over">mapreduce.mapper.inputformat.datastoreinputformat.entitykind</name>
      <value template="optional">User</value>
    </property>

    <property>
      <name human="Destination Namespace">mapreduce.mapper.inputformat.datastoreinputformat.destination</name>
      <value template="optional">dev.mysite.com</value>
    </property>

  </configuration>
</configurations>