saveobj - Customize save process for objects - MATLAB (original) (raw)

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Customize save process for objects

Syntax

Description

Note

The matlab.mixin.CustomElementSerialization class is recommended overloadobj and saveobj because the mixin provides greater control over how objects are serialized and deserialized, including the ability to add, delete, and rename properties. (since R2024b)

[b](#mw%5F3a0881b7-fdd4-4e8d-bf01-63785d4c4c9f) = saveobj([a](#mw%5F2ea8eba9-76fa-465c-9598-90f83415b641)) is called by the save function if the class ofa defines a saveobj method.save writes the returned value, b, to a MAT file.

example

Examples

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The ContactEntry class defines three properties. The class defines asaveobj method that saves those property values in a structure, and aloadobj method that recreates the object from the saved structure.

classdef ContactEntry properties Name Email Cell end methods function s = saveobj(obj) s.Name = obj.Name; s.Email = obj.Email; s.Cell = obj.Cell; end end methods (Static) function obj = loadobj(s) if isstruct(s) newObj = ContactEntry; newObj.Name = s.Name; newObj.Email = s.Email; newObj.Cell = s.Cell; obj = newObj; else obj = s; end end end end

Create an instance of ContactEntry and save it.

a = ContactEntry; a.Name = "Sandy Trent"; a.Email = "strent@notacompany.com"; a.Cell = "617-555-1212"; save("C:_yourpath_\ContactFile.mat","a");

Revise ContactEntry to include a new property that holds a work phone number.

classdef ContactEntry properties Name Email Cell WorkPhone end properties (Transient,Hidden) SaveInOldFormat = false; end methods function s = saveobj(obj) s.Name = obj.Name; s.Email = obj.Email; s.Cell = obj.Cell; if ~obj.SaveInOldFormat s.WorkPhone = obj.WorkPhone; end end end methods (Static) function obj = loadobj(s) if isstruct(s) newObj = ContactEntry; newObj.Name = s.Name; newObj.Email = s.Email; newObj.Cell = s.Cell; if numel(fieldnames(s)) == 4 newObj.WorkPhone = s.WorkPhone; else newObj.WorkPhone = "unknown"; end obj = newObj; else obj = s; end end end end

To maintain compatibility between the two class versions:

The loadobj method has been modified to check for a fourth field in the serialized structure. If there is a fourth field,loadobj sets the WorkPhone property to that value. If not, it sets the WorkPhone property to"unknown".
A new transient, hidden property, SaveInOldFormat, enables class users to specify whether they want to serialize an instance of the class in the old format, without the WorkPhone property value. The saveobj method only saves theWorkPhonevalue if SaveInOldFormat isfalse.

Clear the existing instance a from memory, and loada under the new definition of the class. The revisedloadobj method recognizes the saved data as being from the old version of the class, and sets WorkPhone appropriately.

clear a load("C:_yourpath_\ContactFile.mat","a") a

a =

ContactEntry with properties:

     Name: "Sandy Trent"
    Email: "strent@notacompany.com"
     Cell: "617-555-1212"
WorkPhone: "unknown"

Likewise, you can create a new instance of the class with a value ofWorkPhone, and both the saveobj andloadobj methods save and load the value as expected under the new class definition.

Input Arguments

Output Arguments

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Data passed to save function by MATLAB®, which can be:

An object
Property names and current values stored in a structure

Tips

Implement your saveobj method to work with scalar objects or structures. When you save an object array, save callssaveobj on each element of the array.

Version History

Introduced before R2006a