FIX: Packing values for C++ interaction is much more robust now.

src/Entity.m

@@ -162,9 +162,11 @@ classdef Entity < handle
       res.datatype = obj.datatype_;
       res.unit = obj.unit;
       if (isempty(obj.datatype_))
-        warning(["Trying to transmit an Entity with value but without Datatype.  List-iness is", ...
-                 " unknown, so the value will be omitted."])
-        res.datatype = struct("dtypeName", "UNSPECIFIED", "isList", false, "isReference", false)
+        if ~isempty(obj.value)
+          warning(["Trying to transmit an Entity with value but without Datatype.  List-iness", ...
+                   " is unknown, so the value will be omitted."])
+        end
+        % res.datatype = struct("dtypeName", "UNSPECIFIED", "isList", false, "isReference", false);
         res.value = sparse([]);
       else
         res.value = maox_pack_value(obj.value, obj.datatype_.isList);

src/Property.m

@@ -62,9 +62,11 @@ classdef Property < handle
       res.datatype = obj.datatype_;
       res.unit = obj.unit;
       if (isempty(obj.datatype_))
-        warning(["Trying to transmit an Entity with value but without Datatype.  List-iness is", ...
-                 " unknown, so the value will be omitted."])
-        res.datatype = struct("dtypeName", "UNSPECIFIED", "isList", false, "isReference", false)
+        if ~isempty(obj.value)
+          warning(["Trying to transmit an Entity with value but without Datatype.  List-iness", ...
+                   " is unknown, so the value will be omitted."])
+        end
+        % res.datatype = struct("dtypeName", "UNSPECIFIED", "isList", false, "isReference", false);
         res.value = sparse([]);
       else
         res.value = maox_pack_value(obj.value, obj.datatype_.isList);

src/private/maox_pack_value.m

+% This file is a part of the CaosDB Project.
+%
+% Copyright (C) 2021 IndiScale GmbH <info@indiscale.com>
+% Copyright (C) 2021 Daniel Hornung <d.hornung@indiscale.com>
+%
+% This program is free software: you can redistribute it and/or modify
+% it under the terms of the GNU Affero General Public License as
+% published by the Free Software Foundation, either version 3 of the
+% License, or (at your option) any later version.
+%
+% This program is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU Affero General Public License for more details.
+%
+% You should have received a copy of the GNU Affero General Public License
+% along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+%% Pack the value for handling by maoxdb
+%
+% This means that the value will be packed into a cell array if it is considered a list.
+function result = maox_pack_value(value, isList)
+  % Pack list values into a 1x1 cell array
+  if isList
+    if (isempty(value) && ~ischar(value))  % empty list
+      result = {};
+    else
+      result = {value};
+    end
+  else  % test if value looks scalar
+    if iscellstr(value) || (isnumeric(value) && numel(value) > 1)
+      error("caosdb:valueError", "Value looks list-like, but it must be scalar.");
+    end
+    % handle empty scalar value
+    if (isempty(value) && ~ischar(value))
+      result = sparse([]);
+    else
+      result = value;
+    end
+  end
+end