MongoDB and JAVA - Logical OR with Regex query

Question

I am trying to create an equivalant of the following SQL query:

Select * from X where a like 'a%' OR b like 'a%'

I tried all sorts of options but I keep getting the following error:

falsecom.mongodb.MongoException: $or requires nonempty array

Does anyone know how to do this?

Thanks.

What exactly did you try out in Mongo when you got that exception? — jsalonen
– jsalonen, Commented Jun 18, 2012 at 17:05
You may take inspiration from this [1]: stackoverflow.com/questions/10620771/… — Ravi Khakhkhar
– Ravi Khakhkhar, Commented Jun 18, 2012 at 17:59

jyemin · Accepted Answer · 2012-06-19 12:05:46Z

2

You can use the QueryBuilder class to make the code a bit more readable:

    Mongo m = new Mongo();
    m.setWriteConcern(WriteConcern.SAFE);
    DBCollection c = m.getDB("test").getCollection("or-test");
    c.drop();

    c.insert(new BasicDBObject("a", "abba"));
    c.insert(new BasicDBObject("b", "abba"));
    c.insert(new BasicDBObject("a", "bbba"));
    c.insert(new BasicDBObject("b", "bbba"));

    Pattern pattern = Pattern.compile("^a");
    DBObject query = QueryBuilder.start().or(
            QueryBuilder.start("a").regex(pattern).get(),
            QueryBuilder.start("b").regex(pattern).get()
            ).get();
    System.out.println(c.find(query).count());

This will print "2".

answered Jun 19, 2012 at 12:05

jyemin

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