Question

I write these codes

Query q = pm.newQuery(User.class);
q.setFilter("textPosts != null"); // textPosts is a Text
List<User> users = (List<User>) q.execute();
resp.getWriter().println("user num: " + users.size());

And I get

user num: 0

I’m sure that the number should greater than 0.
I probably miss something important.
Thanks in advance!

Answer 1

Querying Unindexed properties:

A query with a filter or sort order on a property will never match an entity with that property unindexed

So your entity is not found because Text properties are never indexed.

This is also relevant (but in your case Text being unindexed prevails) – entities with non-existing properties are not found with queries:

The App Engine datastore distinguishes between an entity without a given property and an entity with a null value for a property. JDO does not support this distinction: every field of an object has a value, possibly null.

So if you have an Entity without a property, then it will not be found with a query, since a query requires that the property exists.