Serialization with Class Hierarchies - MATLAB & Simulink (original) (raw)
Main Content
When you revise classes in a hierarchy, your hierarchy can inherit frommatlab.mixin.CustomElementSerialization and definemodifyIncomingSerializationContent andmodifyOutgoingSerialization methods to manage the changes.
Call Superclass Methods of matlab.mixin.CustomElementSerialization
In this example, the abstract SensorData superclass is the parent of several subclasses representing different sensors and measurements. In the first version, the superclass defines properties for the data, the first time the data is collected, the interval between data points, and the location of the sensor.
classdef (Abstract) SensorData properties Data {mustBeVector} = 0 StartTime = datetime("today",Format="MMMM d, yyyy HH:mm:ss") Interval = duration(0,1,0) Location {mustBeTextScalar} = "" end end
One of the subclasses, TempData, is designed specifically for temperature data and includes a Units property with validation.
classdef TempData < SensorData properties Units {mustBeMember(Units,["F","C"])} = "C" end end
Create an instance of TempData.
t1 = TempData; t1.Data = [15 17 17 16]; t1.Interval = hours(1); t1.Location = "NW Building 1"
t1 =
TempData with properties:
Units: "C"
Data: [15 17 17 16]
StartTime: June 18, 2024 00:00:00
Interval: 1 hr
Location: "NW Building 1"Save t1 and then clear the instance.
save("yourfilepath/SensorTest.mat","t1") clear t1
In the second version, the SensorData class includes aTimeStamps property. Instead of calculating the time of each data point on demand, this version of the class uses the TimeStamps property to store a vector of times that correspond to each element of theData property. The class implementsmodifyIncomingSerializationContent to add the new property during deserialization, if necessary, and calculate the values based on theStartTime and Interval properties.
classdef (Abstract) SensorData < matlab.mixin.CustomElementSerialization properties Data {mustBeVector} = 0 TimeStamps {mustBeVector} = datetime("today",Format="MMMM d, yyyy HH:mm:ss") StartTime = datetime("today",Format="MMMM d, yyyy HH:mm:ss") Interval = duration(0,1,0) Location {mustBeTextScalar} = "" end methods (Static) function modifyIncomingSerializationContent(sObj) if ~sObj.hasNameValue("TimeStamps") ts(1) = sObj.StartTime; % Set the last value of ts to the StartTime to % preallocate space for the vector. ts(length(sObj.Data)) = sObj.StartTime; for i = 2:length(sObj.Data) ts(i) = ts(i-1) + sObj.Interval; end sObj.addNameValue("TimeStamps",ts); end end end end
To correctly deserialize TempData instances serialized under the older definition of SensorData, the TempData class must implement its own version of modifyIncomingSerializationContent that explicitly calls the superclass modifyIncomingSerializationContent method. MATLAB® does not automatically callmatlab.mixin.CustomElementSerialization methods defined by superclasses. The method first checks if the TimeStamps property exists in the data being deserialized. If not, the method calls the superclassmodifyIncomingSerializationContent method to create it.
classdef TempData < SensorData properties Units {mustBeMember(Units,["F","C"])} = "C" end methods (Static) function modifyIncomingSerializationContent(sObj) if ~sObj.hasNameValue("TimeStamps") modifyIncomingSerializationContent@SensorData(sObj); end end end end
Load the saved instance t1 under the new definitions ofSensorData and TempData. TheTimeStamps property is added.
load("yourfilepath/SensorTest.mat","t1") t1
t1 =
TempData with properties:
Units: "C"
Data: [15 17 17 16]
TimeStamps: [June 18, 2024 00:00:00 June 18, 2024 01:00:00 June 18, 2024 02:00:00 June 18, 2024 03:00:00]
StartTime: June 18, 2024 00:00:00
Interval: 1 hr
Location: "NW Building 1"This example shows how to implement backward compatibility, enabling instances ofTempData serialized under the old definition to be deserialized correctly under the new definition. Forward compatibility is not supported in this particular example. For an example of a class that supports both backward and forward compatibility, see matlab.mixin.CustomElementSerialization.
Customize Serialization in Both Superclasses and Subclasses
Some class revisions require changes to the serialization or deserialization process in both the superclass and a subclass, and the order of those changes can be important. In this example, change the datetime display format of theTimeStamps property from "MMMM d, yyyy HH:mm:ss" to "dd-MMM-uuuu HH:mm". To apply this format change to TempData but not the other subclasses ofSensorData, make the change in TempData.
Create an instance of TempData using the first version of the class.
t2 = TempData; t2.Data = [18 18 17 18]; t2.Interval = minutes(30); t2.Location = "NW Building 1"
t2 =
TempData with properties:
Units: "C"
Data: [18 18 17 18]
StartTime: June 19, 2024 00:00:00
Interval: 30 min
Location: "NW Building 1"Save t2 and then clear the instance.
save("yourfilepath/SensorTest2.mat","t2") clear t2
Update the second version of the TempData class. ThemodifyIncomingSerializationContent method must first call the superclass method and then apply the format change to the newly createdTimeStamps property.
classdef TempData < SensorData properties Units {mustBeMember(Units,["F","C"])} = "C" end methods (Static) function modifyIncomingSerializationContent(sObj) if ~sObj.hasNameValue("TimeStamps") modifyIncomingSerializationContent@SensorData(sObj); end sObj.TimeStamps = datetime(sObj.TimeStamps,Format="dd-MMM-uuuu HH:mm"); end end end
Load the instance t2 under the latest definitions ofSensorData and TempData. The superclass method adds theTimeStamps property, and the subclass method reformats the data in TimeStamps.
load("yourfilepath/SensorTest2.mat","t2") t2
t2 =
TempData with properties:
Units: "C"
Data: [18 18 17 18]
TimeStamps: [19-Jun-2024 00:00 19-Jun-2024 00:30 19-Jun-2024 01:00 19-Jun-2024 01:30]
StartTime: June 19, 2024 00:00:00
Interval: 30 min
Location: "NW Building 1"See Also
matlab.mixin.CustomElementSerialization | matlab.serialization.ElementSerializationContent | matlab.serialization.SerializationContext