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
return firstLevelMd;
        
        if( ! firstLevelMd.hasChildDocuments() )
            return null;    
        
        String childFullName = stripParentName( fieldFullName, nameFragments[0] );
        return findFieldByFullName( childFullName, firstLevelMd.getChildMetaData() );
    }
    /**
     * Indicates whether the specified field has flattening support.
     * @param fieldMd   field metadata; may be that of top-level array field or a child field
     * @param topLevelDocMD     top level document metadata returned 
     *          by {@link #getAvailableFields(String, int, QueryProperties)}
     */
    public static boolean isFlattenableNestedField( FieldMetaData fieldMd, DocumentsMetaData topLevelDocMD )
    {
        if( fieldMd == null )
            return false;
        DocumentsMetaData containingDocMD = fieldMd.getContainingMetaData();
        if( containingDocMD == null )   
        {
            containingDocMD = topLevelDocMD;   
        }
        String cachedAncestorName = containingDocMD.getFlattenableFieldName();
        if( cachedAncestorName != null && cachedAncestorName.equals( fieldMd.getFullName() ))
            return true;
        if( fieldMd.isChildField() )
            return isFlattenableNestedField( fieldMd.getParentMetaData(), topLevelDocMD );
        return false;
    }