GAE: JAVA- update only one field in a particular row of an entity

Question

The requirement is to update the field of one of the rows in the entity. But the below code is updating entity row. Where am I making a mistake?

//Inserting
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();

//Util.getKey() always returns current Date    
Key ky=KeyFactory.createKey("Routine", Util.getKey());

Entity e = new Entity("Routine",ky);
e.setProperty("running", Constants.RUNNING_INCREDIBLE);
datastore.put(e);

//Updating 
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
Key ky=KeyFactory.createKey("Routine", Util.getKey());

Entity e2=datastore.get(ky);    

e2.setProperty("bAS", Constants.BAS_INCREDIBLE);
datastore.put(e);

Answer 1

There is nothing wrong with your implementation. There is no difference between insert and update in Datastore.

From the documentation:

The Cloud Datastore API does not distinguish between creating a new entity and updating an existing one . If the object's key represents an entity that already exists, the put() method overwrites the existing entity. You can use a transaction to test whether an entity with a given key exists before creating one.

You can refer to the documentation.

Additionally, if you are updating a field too quickly consider using MemCache.

If you want to take care of transactions, look at:

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
Transaction txn = datastore.beginTransaction();
try {
  Key employeeKey = KeyFactory.createKey("Employee", "Joe");
  Entity employee = datastore.get(employeeKey);
  employee.setProperty("vacationDays", 10);

  datastore.put(txn, employee);

  txn.commit();
} finally {
  if (txn.isActive()) {
    txn.rollback();
  }
}

This is documented here