JAVA-549: Removed unnecessary fake iterator for queries with 0 results. Simplifies the code, and also fixes this bug, because now every DBCursor will have a server address, even one with no results. Note that you still have to call hasNext() or next() at least once to get a non-null server address, since queries are done lazily

Author: jyemin

src/main/com/mongodb/DBApiLayer.java

@@ -312,9 +312,6 @@ Iterator<DBObject> __find( DBObject ref , DBObject fields , int numToSkip , int
 
             Response res = _connector.call( _db , this , query , null , 2, readPref, decoder );
 
-            if ( res.size() == 0 )
-                return null;
-
             if ( res.size() == 1 ){
                 BSONObject foo = res.get(0);
                 MongoException e = MongoException.parse( foo );

src/main/com/mongodb/DBCollection.java

@@ -334,7 +334,7 @@ public DBObject findOne( Object obj )
      */
     public DBObject findOne( Object obj, DBObject fields ) {
         Iterator<DBObject> iterator = __find( new BasicDBObject("_id", obj), fields, 0, -1, 0, getOptions(), getReadPreference(), getDecoder() );
-        return (iterator != null ? iterator.next() : null);
+        return (iterator.hasNext() ? iterator.next() : null);
     }
 
     /**
@@ -649,7 +649,7 @@ public DBObject findOne( DBObject o, DBObject fields ) {
      */
     public DBObject findOne( DBObject o, DBObject fields, ReadPreference readPref ) {
         Iterator<DBObject> i = __find( o , fields , 0 , -1 , 0, getOptions(), readPref, getDecoder() );
-        DBObject obj = (i == null ? null : i.next());
+        DBObject obj = (i.hasNext() ? i.next() : null);
         if ( obj != null && ( fields != null && fields.keySet().size() > 0 ) ){
             obj.markAsPartialObject();
         }

src/main/com/mongodb/DBCursor.java

@@ -59,12 +59,13 @@ public class DBCursor implements Iterator<DBObject> , Iterable<DBObject>, Closea
      * @param preference the Read Preference for this query
      */
     public DBCursor( DBCollection collection , DBObject q , DBObject k, ReadPreference preference ){
+        if (collection == null) {
+            throw new IllegalArgumentException("collection is null");
+        }
         _collection = collection;
         _query = q == null ? new BasicDBObject() : q;
         _keysWanted = k;
-        if ( _collection != null ){
-            _options = _collection.getOptions();
-        }
+        _options = _collection.getOptions();
         _readPref = preference;
         _decoderFact = collection.getDBDecoderFactory();
     }
@@ -346,34 +347,26 @@ private void _check()
         if ( _it != null )
             return;
 
-        if ( _collection != null && _query != null ){
-
-            _lookForHints();
-
-            DBObject foo = _query;
-            if ( hasSpecialQueryFields() ){
-                foo = _specialFields == null ? new BasicDBObject() : _specialFields;
+        _lookForHints();
 
-                _addToQueryObject( foo , "query" , _query , true );
-                _addToQueryObject( foo , "orderby" , _orderBy , false );
-                if(_hint != null)
-                    _addToQueryObject( foo , "$hint" , _hint );
-                if(_hintDBObj != null)
-                    _addToQueryObject( foo , "$hint" , _hintDBObj);
+        DBObject foo = _query;
+        if (hasSpecialQueryFields()) {
+            foo = _specialFields == null ? new BasicDBObject() : _specialFields;
 
-                if ( _explain )
-                    foo.put( "$explain" , true );
-                if ( _snapshot )
-                    foo.put( "$snapshot", true );
-            }
+            _addToQueryObject(foo, "query", _query, true);
+            _addToQueryObject(foo, "orderby", _orderBy, false);
+            if (_hint != null)
+                _addToQueryObject(foo, "$hint", _hint);
+            if (_hintDBObj != null)
+                _addToQueryObject(foo, "$hint", _hintDBObj);
 
-            _it = _collection.__find( foo, _keysWanted, _skip, _batchSize, _limit , _options , _readPref , getDecoder());
+            if (_explain)
+                foo.put("$explain", true);
+            if (_snapshot)
+                foo.put("$snapshot", true);
         }
 
-        if ( _it == null ){
-            _it = (new LinkedList<DBObject>()).iterator();
-            _fake = true;
-        }
+        _it = _collection.__find(foo, _keysWanted, _skip, _batchSize, _limit, _options, _readPref, getDecoder());
     }
 
     // Only create a new decoder if there is a decoder factory explicitly set on the collection.  Otherwise return null
@@ -477,9 +470,6 @@ private DBObject _next()
      * @return
      */
     public int numGetMores(){
-        if ( _fake )
-            return 0;
-
         if ( _it instanceof DBApiLayer.Result )
             return ((DBApiLayer.Result)_it).numGetMores();
 
@@ -491,9 +481,6 @@ public int numGetMores(){
      * @return
      */
     public List<Integer> getSizes(){
-        if ( _fake )
-            return new LinkedList<Integer>();
-
         if ( _it instanceof DBApiLayer.Result )
             return ((DBApiLayer.Result)_it).getSizes();
 
@@ -765,7 +752,6 @@ public String toString() {
 
     // ----  result info ----
     private Iterator<DBObject> _it = null;
-    private boolean _fake = false;
 
     private CursorType _cursorType = null;
     private DBObject _cur = null;