Google App Engine查询无法在Java中运行

Question

Riddle me this Stackoverflow:

I have a query that I am sending to GAE. The query (When in String format) looks like this: SELECT * FROM USER WHERE USER_ID = 5884677008

If I go to the GAE console and type it in via a manual GQL query, it returns the item just fine. If I browse via the GUI and scroll to it, I can see it just fine. But when I call it from the Java code, it returns nothing every time. code:

I have already confirmed the query is correct as I printed it out as a String just so I can test it.

Anyone have any idea what is going on with this?

    q = new Query(entityName); //entityName = "User", confirmed
    q.setFilter(filter); //filter = "USER_ID = 5884677008", confirmed
    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
    PreparedQuery pq = datastore.prepare(q);
    /*
    This always is empty here. Calling either pq.countEntities()); or
    pq.toString()); returns size 0 or a String of nothing.
    */

Thanks! -Sil

Edit: I Do have an index built, but it did not seem to help with the problem.

Answer 1

From the docs , you don't necessarily need to do toString. Have you tried asIterable or asSingleEntity on pq? Something like:

PreparedQuery pq = datastore.prepare(q);

for (Entity result : pq.asIterable()) {
  String test = (String) result.getProperty("prop1");
}

That's if you have multiple entries. In the event you only have one:

PreparedQuery pq = datastore.prepare(q);

Entity result = pq.asSingleEntity();
String test = (String) result.getProperty("prop1");

Basically, if you don't call asIterable or asSingleEntity, the query is JUST prepared and doesn't run

Answer 2

Took quite a bit of testing, but found the issue.

The problem revolved around the filter being set. If I removed the filter, it worked fine (but returned everything). Turns out, what was being passed as a filter was a String version of the user_id as opposed to the Long version of it. There was really no way to tell as the exact SQL query DID NOT read ( SELECT * FROM USER WHERE USER_ID = "5884677008" ) when I printed it, which would have been a dead giveaway.

I changed the passed filter parameter (which I had stored in a hashmap of (String, Object) btw) from a String to a Long and that solved the issue.

One thing to point out though, as @Patrice brought up (And as I excluded from my code while posting to save space), to actually iterate through the list of results, you do need to call a method against it (Either .asIterable() or .asSingleEntity() ).

You actually can check against the number of returned entities / results by calling pq.countEntities() and it will return the correct number even before you call a formatting method against the pq, but as @tx802 pointed out, it is deprecated, and despite the fact that it worked for me, someone in the future using this post as a reference may not have it work for them.