Bug 416703 Mongodb : Display correctly the Number data type
data/org.eclipse.birt.data.oda.mongodb/src/org/eclipse/birt/data/oda/mongodb/internal/impl/MDbMetaData.java
fieldMd = new FieldMetaData( fieldName );
                fieldMd.setParentMetaData( parentMd );
            }
            fieldMd.addDataType( fieldValue );
            m_fieldsMetaData.put( fieldMd.getSimpleName(), fieldMd );
            return fieldMd;
        }
        @SuppressWarnings("unused")
        private void removeField( String fieldName )
        {
            if( fieldName != null )
                m_fieldsMetaData.remove( fieldName );
        }
          
        /**
         * Returns the simple names of first level fields in the sequence that 
         * they were discovered from a collection.
         */
        public List<String> getFieldNames()
        {
            
            List<String> docFields = new ArrayList<String>(m_fieldsMetaData.size());
            for( String fieldName : m_fieldsMetaData.keySet() )
            {
                docFields.add( fieldName );
            }
            return docFields;
        }
        /**
         * Returns the simple names of first level fields in natural ascending order.