When encoding a DBObject, if a value implements both Iterable and Map, encode it as a document rather than array. This preserves compatibility with 2.x encoding behavior.

 JAVA-1760

Author: jyemin

driver/src/main/com/mongodb/DBObjectCodec.java

@@ -192,10 +192,10 @@ private void writeValue(final BsonWriter bsonWriter, final EncoderContext encode
             bsonWriter.writeNull();
         } else if (value instanceof DBRef) {
             encodeDBRef(bsonWriter, (DBRef) value);
-        } else if (value instanceof Iterable) {
-            encodeIterable(bsonWriter, (Iterable) value);
         } else if (value instanceof Map) {
             encodeMap(bsonWriter, (Map<String, Object>) value);
+        } else if (value instanceof Iterable) {
+            encodeIterable(bsonWriter, (Iterable) value);
         } else if (value instanceof BSONObject) {
             encodeBsonObject(bsonWriter, ((BSONObject) value));
         } else if (value instanceof CodeWScope) {

driver/src/test/functional/com/mongodb/DBObjectCodecTest.java

@@ -31,6 +31,7 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 
@@ -177,4 +178,28 @@ public void shouldEncodedNestedMapsListsAndDocuments() {
                      .append("lazyDoc", zeroOneBsonDocument)
                      .append("lazyArray", zeroOneBsonArray), writer.getDocument());
     }
+
+    @Test
+    public void shouldEncodeIterableMapAsMap() {
+        IterableMap iterableMap = new IterableMap();
+        iterableMap.put("first", 1);
+
+        DBObjectCodec dbObjectCodec = new DBObjectCodec(fromProviders(asList(new ValueCodecProvider(), new DBObjectCodecProvider())));
+
+        DBObject doc = new BasicDBObject("map", iterableMap);
+
+        BsonDocumentWriter writer = new BsonDocumentWriter(new BsonDocument());
+        dbObjectCodec.encode(writer, doc, EncoderContext.builder().build());
+
+        assertEquals(new BsonDocument("map", new BsonDocument("first", new BsonInt32(1))), writer.getDocument());
+    }
+
+    static class IterableMap extends HashMap<String, Integer> implements Iterable<Integer> {
+        private static final long serialVersionUID = -5090421898469363392L;
+
+        @Override
+        public Iterator<Integer> iterator() {
+            return values().iterator();
+        }
+    }
 }