NotSupportedException: The property Title is read-only

Few lines of code which are quite self-explanatory and used to be working in pre-EPiServer 5 era.

// get page instance
PageData page = DataFactory.Instance.GetPage(new PageReference(id));

// set new value
page.Property["Title"].Value = "here comes some new value!!!";

// save and publish
DataFactory.Instance.Save(page, SaveAction.Publish);

Looks nice and easy ... but there is one problem ... it throws an System.NotSupportedException saying that "The property Title is read-only."

You can use DataFactory.Instance.GetPage() method to load pages but EPiServer 5 will return read-only instance of the page. Compiler will not complain that you are assigning new value to the read-only property but in a runtime you will get the exception. If your goal is to update a page you should use this method to get modifiable instance: PageData.CreateWritableClone()

and it whole should looks like that:

// get read-only page instance
PageData readonlyPage = DataFactory.Instance.GetPage(new PageReference(id));

// get modifiable instance
PageData modifiablePage = readonlyPage.CreateWritableClone();

// set new value
modifiablePage.Property["Title"].Value = "here comes some new value!!!";

// save and publish
DataFactory.Instance.Save(modifiablePage, SaveAction.Publish);

Why EPiServer 5 forces us to write this one extra line of code? Answer is performance! Returning read-only instances is significantly faster and moreover ... in most cases that is what you really need. I guess that in 90% of cases you are accessing data simply to display it for the users. In the rest, 10% cases, you want to update those data. It makes perfect sense to have it working faster in typical cases and to write one additional line of code when you want to modify properties.