How to set a dynamic property as transient?

Consider the following example which defines a class that contains a dynamic property 'bigData'. When the class gets saved, 'bigData' gets saved along with the other properties of the class. Later, the "Transient" attribute of the dynamic property is set true. In the subsequent save operation, 'bigData' should not be saved with the other class properties, however, the size of the resulting file is the same for Transient=true as it is for Transient=false. The Transient attribute does not appear to have any affect on the size of the saved file. What is needed to get the Transient attribute to take effect?

classdef (ConstructOnLoad = true) TestDynProps < dynamicprops
    properties
        a;
        dp;
    end
    
    methods
        function this = TestDynProps()
            this.a = [];
            this.dp = addprop(this, 'bigData');
        end
        
        function testSave(this)
            this.a = [2,4,6,8];
            this.bigData = rand([1000, 1000]);
            
            save("transient_false.mat", 'this')
            
            this.dp.Transient = true;
            save("transient_true.mat", 'this')
        end
    end
end

>> tdp = TestDynProps()

tdp = 

  TestDynProps with properties:

          a: []
         dp: [1×1 meta.DynamicProperty]
    bigData: []

>> tdp.testSave()

Answer 1

[Kautuk Raj]

From what I gather, you are seeking clarification on why setting the Transient attribute to true for a dynamic property in MATLAB does not reduce the size of the saved file and what changes are necessary to ensure the attribute effectively excludes the property from being saved.

The Transient attribute for dynamic properties in MATLAB is designed to indicate whether a property should be saved when the object is saved to a file. If the Transient attribute is set to true, the property should not be saved. However, in the given example, setting the Transient attribute to true just before saving does not seem to exclude “bigData” from being saved.

To ensure that the Transient attribute takes effect, you should modify the class definition to allow the dynamic property to be configured properly before any save operation is attempted. Here is how you could modify the “TestDynProps” class to achieve this:

classdef (ConstructOnLoad = true) TestDynProps < dynamicprops 
    properties 
        a; 
    end 
    
    methods 
        function this = TestDynProps() 
            this.a = []; 
            this.addBigDataProperty(false); % initially not transient 
        end 
        
        function addBigDataProperty(this, isTransient) 
            if isprop(this, 'bigData') 
                delete(this.findprop('bigData')); 
            end 
            dp = this.addprop('bigData'); 
            dp.Transient = isTransient; 
        end 
        
        function testSave(this) 
            this.a = [2,4,6,8]; 
            this.bigData = rand([1000, 1000]); 
            
            save("transient_false.mat", 'this') 
            
            this.addBigDataProperty(true); % now make it transient 
            save("transient_true.mat", 'this') 
        end 
    end 
end 

The modified class uses the “addBigDataProperty” method to manage the “bigData” dynamic property's Transient attribute, ensuring it is set appropriately before each save operation within the “testSave” method.

More about the Transient property can be gathered from the MathWorks documentation page below: https://www.mathworks.com/help/releases/R2020b/matlab/matlab_oop/property-attributes.html#:~:text=and%20Query%20Events-,Transient,-logical