Hi,

You can use Content Events. Like - Publishing, Published events

https://marisks.net/2017/01/22/episerver-content-events-explained/

https://world.episerver.com/blogs/Daniel-Ovaska/Dates/2019/6/content-events-in-episerver/

https://www.jondjones.com/learn-episerver-cms/episerver-developers-tutorials/episerver-event-handling/how-to-hook-into-the-episerver-cms-events-pipeline/

You can create a scheduled job, or an admin tool that will:

• Get all pages of a specific type
• For every page
  • Check if the property is null
    • Create writable clone of the page
    • Update property
    • Save

Or, lets say your property is of type string, and you want to set it's default value some time after adding it.

You could probably do:

[PropertyDefinitionTypePlugIn]
public class PropertyStringWithDefaultHackValue : PropertyString
{
     public override object Value => base.Value ?? "Hack";
}

And then change your property on your content type to:

[Display(Name = "This should work")]
[BackingType(typeof(PropertyStringWithDefaultHackValue))]
public virtual string MyString { get; set; }

Ok tried the IInitializableModule and get an exception:

The property XXX is read-only

How do I make it writable? There is no overload called "MakeWritable" or something as far as I can see.

Note! This is a IList that I try to initiate from null in this instance.

What Tomas suggested does not work. At least not in a already custom property type. Any other ideas?

public class CustomInnerProperty
{
     [Display(Order = 900, Name = "Id")]
     [BackingType(typeof(StringAsGuidDescriptor))]
     public virtual string Id { get; set; } = Guid.NewGuid().ToString();

}

[PropertyDefinitionTypePlugIn]
public class StringAsGuidDescriptor : PropertyString
{
    public override object Value
    {
       get => string.IsNullOrEmpty(base.String) ? Guid.NewGuid().ToString() : base.String;
       set => SetPropertyValue(value, () => base.String = value?.ToString());
    }
}

public class CustomInnerPropertyDescriptor : CollectionEditorDescriptor<CustomInnerProperty>
{
   public CustomInnerPropertyDescriptor()
   {
      GridDefinition.DisableDndSorting = true;
   }
}

public class CustomOuterProperty
{
   [Required]
   [Display(Order = 100, Name = "Items")]
   [EditorDescriptor(EditorDescriptorType = typeof(CustomInnerPropertyDescriptor))]
   public virtual IList<CustomInnerProperty> Items { get; set; }
}