Google App Engine: Is it possible to do a Gql LIKE

Question

Simple one really. In SQL, if I want to search a text field for a couple of characters, I can do:

SELECT blah FROM blah WHERE blah LIKE '%text%'

The documentation for App Engine makes no mention of how to achieve this, but surely it's a common enough problem?

Answer 1

I tested this with GAE Datastore low-level Java API. Me and works perfectly

    Query q = new Query(Directorio.class.getSimpleName());

    Filter filterNombreGreater = new FilterPredicate("nombre", FilterOperator.GREATER_THAN_OR_EQUAL, query);
    Filter filterNombreLess = new FilterPredicate("nombre", FilterOperator.LESS_THAN, query+"\uFFFD");
    Filter filterNombre =  CompositeFilterOperator.and(filterNombreGreater, filterNombreLess);

    q.setFilter(filter);

Answer 2

Just follow here: init.py#354">http://code.google.com/p/googleappengine/source/browse/trunk/python/google/appengine/ext/search/init.py#354

It works!

class Article(search.SearchableModel):
    text = db.TextProperty()
    ...

  article = Article(text=...)
  article.save()

To search the full text index, use the SearchableModel.all() method to get an
instance of SearchableModel.Query, which subclasses db.Query. Use its search()
method to provide a search query, in addition to any other filters or sort
orders, e.g.:

  query = article.all().search('a search query').filter(...).order(...)

Answer 3

"Like" is often uses as a poor-man's substitute for text search. For text search, it is possible to use Whoosh-AppEngine.

Answer 4

If the LIKE '%text%' always compares to a word or a few (think permutations) and your data changes slowly (slowly means that it's not prohibitively expensive - both price-wise and performance-wise - to create and updates indexes) then Relation Index Entity (RIE) may be the answer.

Yes, you will have to build additional datastore entity and populate it appropriately. Yes, there are some constraints that you will have to play around (one is 5000 limit on the length of list property in GAE datastore). But the resulting searches are lightning fast.

For details see my RIE with Java and Ojbectify and RIE with Python posts.

Answer 5

Have a look at Objectify here , it is like a Datastore access API. There is a FAQ with this question specifically, here is the answer

How do I do a like query (LIKE "foo%")
You can do something like a startWith, or endWith if you reverse the order when stored and searched. You do a range query with the starting value you want, and a value just above the one you want.

String start = "foo";
    ... = ofy.query(MyEntity.class).filter("field >=", start).filter("field <", start + "\uFFFD");

Answer 6

Altough App Engine does not support LIKE queries, have a look at the properties ListProperty and StringListProperty. When an equality test is done on these properties, the test will actually be applied on all list members, e.g., list_property = value tests if the value appears anywhere in the list.

Sometimes this feature might be used as a workaround to the lack of LIKE queries. For instance, it makes it possible to do simple text search, as described on this post.