无法删除在Java GAE中设置了特定属性的实体

Question

I have the entities created like this:

public String addNewStockName(String newStock) throws DelistedException {
    Entity stock = new Entity("Stocks");
    stock.setProperty("Name", newStock);
    ds.put(stock);
    return "OK";
}

Trying delete the specific entity like this:

public String deleteStockName(String stockName){
    Key key = KeyFactory.createKey("Stocks", stockName);
    ds.delete(key);
    return "OK";
}

And it does not delete the entity which has property 'stockName'. Why?

Answer 1

If you want to create an entity that you can fetch by stockName , you need something like

public String addNewStockName(String stockName) throws DelistedException {
    Key key = KeyFactory.createKey("Stocks", stockName);
    Entity stock = new Entity(key);
    stock.setProperty("foo", "bar");
    ds.put(stock);
    return "OK";
}

You can then use your deleteStockName() method as is. This of course assumes your key name is unique, but it also means you can always fetch the Stock by key, rather than query.

Answer 2

Your Stocks entity has a property named "Name" . That is not the same as the key name .

You have to perform a query to get the entities or entity keys matching the filter of "Name=?" .

Something like this:

public String deleteStockName(String stockName) {
    DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
    Filter f = new FilterPredicate("Name", FilterOperator.EQUAL, stockName);
    Query q = new Query("Stocks").setFilter(f).setKeysOnly();

    List<Entity> results = ds.prepare(q)
            .asList(FetchOptions.Builder.withDefaults());
    if (results.isEmpty())
        return "Not Found!";

    ds.delete(results.get(0).getKey());
    return "OK";
}