Querying in a array of String with Java driver

[The JMCNet Team]

Hello,

Here is a view of my DB :
> db.userGroup.find().pretty()
{
        "_id" : "512DEA59178020D87F668A2F",
        "adminAccountIds" : [
                "512DEA4F178020D87F668A2D"
        ]
}
{
        "_id" : "512DEA4F178020D87F668A2E",
        "adminAccountIds" : [
                "512DEA4F178020D87F668A2D",
                "512DEA4F178020D87F668A2G",
        ]
}
I want to query all userGroup that have a adminAccountIds equals to a parameter.

In console I've done this :
db.userGroup.find('{ "adminAccountIds" : { "$elemMatch" : "512DEA4F178020D87F668A2D"}}').pretty()
and it works.

I try to do the same programmatically with the Java driver :
DBCollection userGroup = db.getCollection("userGroup");
        BasicDBObject query = new BasicDBObject("adminAccountIds", new BasicDBObject("$elemMatch", "512DEA4F178020D87F668A2D"));
        DBCursor qRes = userGroup.find(
                query, new BasicDBObject("_id", 1));

but the result is :
com.mongodb.MongoException: invalid parameter: expected an object ($elemMatch)
    at com.mongodb.MongoException.parse(MongoException.java:82)

Any idea would be greatly appreciated.

Thank's in advance.

[Russell Bateman]

Here's a scrape of my DAO code. In POJO Account, field identities is defined thus:

public class AccoundDao
{
    ....
    private List< String > identities;
    ....
}

This returns an array of all the documents whose identities array contains at least the string identity.

      public List< Account > readAllByIdentity( String identity )
    {
        List< Account > list  = new ArrayList< Account >();
        BasicDBObject   query = new BasicDBObject();
        query.put( "identities", identity );
        query.put( "forgotten", false );
        DBCursor cursor = getCollection().find( query );

        while( cursor.hasNext() )
        {
            DBObject dbo = cursor.next();

            Account account = new Account();
            account.makePojoFromBson( dbo );

            list.add( account );
        }

        return list;
    }

Hope this helps.

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[The JMCNet Team]

It works perfectly but I don't understand why ... How MongoDB understand that this simple query : query.put( "identities", identity );
means "where identity in identities" ? Is there a special treatment MongoDB side for Array of String ?

JM.

[Russell Bateman]

Yeah, I know what you mean. I think someone in this forum put me on to this or an instructor at one of the 10gen courses I attended. I learned it in JavaScript first, then created the Java from that. It was an exercise of pure faith for me too.

My code is about 70%-80% Morphia, which works very well and obviates the whole makePojoFromBson() method I coded (and found nasty, awkward). This is one of the lone things remaining in pure Java BasicDBObject. For now, I'm saying that if it ain't broke, don't fix it.

Best regards,

Russ